| Message ID | 20230626082353.18535-4-avihaih@nvidia.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | vfio/migration: Make VFIO migration non-experimental | expand |
Hello Avihai, On 6/26/23 10:23, Avihai Horon wrote: > The major parts of VFIO migration are supported today in QEMU. This > includes basic VFIO migration, device dirty page tracking and precopy > support. > > Thus, at this point in time, it seems appropriate to make VFIO migration > non-experimental: remove the x prefix from enable_migration property, > change it to ON_OFF_AUTO and let the default value be AUTO. > > In addition, make the following adjustments: > 1. Require device dirty tracking support when enable_migration is AUTO > (i.e., not explicitly enabled). This is because device dirty tracking > is currently the only method to do dirty page tracking, which is > essential for migrating in a reasonable downtime. hmm, I don't think QEMU should decide to disable a feature for all devices supposedly because it could be slow for some. That's too restrictive. What about devices with have small states ? for which the downtime would be reasonable even without device dirty tracking support. > Setting > enable_migration to ON will not require device dirty tracking. > 2. Make migration blocker messages more elaborate. > 3. Remove error prints in vfio_migration_query_flags(). > 4. Remove a redundant assignment in vfio_migration_realize(). > > Signed-off-by: Avihai Horon <avihaih@nvidia.com> > --- > include/hw/vfio/vfio-common.h | 2 +- > hw/vfio/migration.c | 29 ++++++++++++++++------------- > hw/vfio/pci.c | 4 ++-- > 3 files changed, 19 insertions(+), 16 deletions(-) > > diff --git a/include/hw/vfio/vfio-common.h b/include/hw/vfio/vfio-common.h > index b4c28f318f..387eabde60 100644 > --- a/include/hw/vfio/vfio-common.h > +++ b/include/hw/vfio/vfio-common.h > @@ -139,7 +139,7 @@ typedef struct VFIODevice { > bool needs_reset; > bool no_mmap; > bool ram_block_discard_allowed; > - bool enable_migration; > + OnOffAuto enable_migration; > VFIODeviceOps *ops; > unsigned int num_irqs; > unsigned int num_regions; > diff --git a/hw/vfio/migration.c b/hw/vfio/migration.c > index 79eb81dfd7..d8e0848635 100644 > --- a/hw/vfio/migration.c > +++ b/hw/vfio/migration.c > @@ -731,14 +731,6 @@ static int vfio_migration_query_flags(VFIODevice *vbasedev, uint64_t *mig_flags) > feature->argsz = sizeof(buf); > feature->flags = VFIO_DEVICE_FEATURE_GET | VFIO_DEVICE_FEATURE_MIGRATION; > if (ioctl(vbasedev->fd, VFIO_DEVICE_FEATURE, feature)) { > - if (errno == ENOTTY) { > - error_report("%s: VFIO migration is not supported in kernel", > - vbasedev->name); > - } else { > - error_report("%s: Failed to query VFIO migration support, err: %s", > - vbasedev->name, strerror(errno)); > - } > - > return -errno; > } > > @@ -831,14 +823,28 @@ void vfio_reset_bytes_transferred(void) > > int vfio_migration_realize(VFIODevice *vbasedev, Error **errp) > { > - int ret = -ENOTSUP; > + int ret; > > - if (!vbasedev->enable_migration) { > + if (vbasedev->enable_migration == ON_OFF_AUTO_OFF) { > + error_setg(&vbasedev->migration_blocker, > + "%s: Migration is disabled for VFIO device", vbasedev->name); > goto add_blocker; > } > > ret = vfio_migration_init(vbasedev); > if (ret) { It would be good to keep the message for 'errno == ENOTTY' as it was in vfio_migration_query_flags(). When migration fails, it is an important information to know that it is because the VFIO PCI host device driver doesn't support the feature. The root cause could be deep below in FW or how the VF was set up. > + error_setg(&vbasedev->migration_blocker, > + "%s: Migration couldn't be initialized for VFIO device, " > + "err: %d (%s)", > + vbasedev->name, ret, strerror(-ret)); > + goto add_blocker; > + } > + > + if (vbasedev->enable_migration == ON_OFF_AUTO_AUTO && > + !vbasedev->dirty_pages_supported) { I don't agree with this test. > + error_setg(&vbasedev->migration_blocker, > + "%s: VFIO device doesn't support device dirty tracking", > + vbasedev->name); > goto add_blocker; > } I agree that with ON_OFF_AUTO_AUTO, errors at realize time should be recorded in a migration blocker. What about the ON_OFF_AUTO_ON case ? If migration was explicitly requested for the device and the conditions on the host are not met, I think realize should fail and the machine abort. Thanks, C. > @@ -856,9 +862,6 @@ int vfio_migration_realize(VFIODevice *vbasedev, Error **errp) > return 0; > > add_blocker: > - error_setg(&vbasedev->migration_blocker, > - "VFIO device doesn't support migration"); > - > ret = migrate_add_blocker(vbasedev->migration_blocker, errp); > if (ret < 0) { > error_free(vbasedev->migration_blocker); > diff --git a/hw/vfio/pci.c b/hw/vfio/pci.c > index 73874a94de..48584e3b01 100644 > --- a/hw/vfio/pci.c > +++ b/hw/vfio/pci.c > @@ -3347,8 +3347,8 @@ static Property vfio_pci_dev_properties[] = { > VFIO_FEATURE_ENABLE_REQ_BIT, true), > DEFINE_PROP_BIT("x-igd-opregion", VFIOPCIDevice, features, > VFIO_FEATURE_ENABLE_IGD_OPREGION_BIT, false), > - DEFINE_PROP_BOOL("x-enable-migration", VFIOPCIDevice, > - vbasedev.enable_migration, false), > + DEFINE_PROP_ON_OFF_AUTO("enable-migration", VFIOPCIDevice, > + vbasedev.enable_migration, ON_OFF_AUTO_AUTO), > DEFINE_PROP_BOOL("x-no-mmap", VFIOPCIDevice, vbasedev.no_mmap, false), > DEFINE_PROP_BOOL("x-balloon-allowed", VFIOPCIDevice, > vbasedev.ram_block_discard_allowed, false),
On 26/06/2023 14:20, Cédric Le Goater wrote: > Hello Avihai, > > On 6/26/23 10:23, Avihai Horon wrote: >> The major parts of VFIO migration are supported today in QEMU. This >> includes basic VFIO migration, device dirty page tracking and precopy >> support. >> >> Thus, at this point in time, it seems appropriate to make VFIO migration >> non-experimental: remove the x prefix from enable_migration property, >> change it to ON_OFF_AUTO and let the default value be AUTO. >> >> In addition, make the following adjustments: >> 1. Require device dirty tracking support when enable_migration is AUTO >> (i.e., not explicitly enabled). This is because device dirty tracking >> is currently the only method to do dirty page tracking, which is >> essential for migrating in a reasonable downtime. > > hmm, I don't think QEMU should decide to disable a feature for all > devices supposedly because it could be slow for some. That's too > restrictive. What about devices with have small states ? for which > the downtime would be reasonable even without device dirty tracking > support. > device dirty tracking refers to the ability to tracking dirty IOVA used by the device which will DMA into RAM. It is required because the consequence/alternative is to transfer all RAM in stop copy phase. Device state size at that point is the least of our problems downtime wise. I can imagine that allowing without dirty tracking is useful for developer testing of the suspend/device-state flows, but as real default (auto) is very questionable to let it go through without dirty tracking. When we have IOMMUFD dirty tracking that's when we can relieve this restriction as a default. But then note that (...) > >> Setting >> enable_migration to ON will not require device dirty tracking. (...) this lets it ignore dirty tracking as you would like. >> 2. Make migration blocker messages more elaborate. >> 3. Remove error prints in vfio_migration_query_flags(). >> 4. Remove a redundant assignment in vfio_migration_realize(). >> >> Signed-off-by: Avihai Horon <avihaih@nvidia.com> >> --- >> include/hw/vfio/vfio-common.h | 2 +- >> hw/vfio/migration.c | 29 ++++++++++++++++------------- >> hw/vfio/pci.c | 4 ++-- >> 3 files changed, 19 insertions(+), 16 deletions(-) >> >> diff --git a/include/hw/vfio/vfio-common.h b/include/hw/vfio/vfio-common.h >> index b4c28f318f..387eabde60 100644 >> --- a/include/hw/vfio/vfio-common.h >> +++ b/include/hw/vfio/vfio-common.h >> @@ -139,7 +139,7 @@ typedef struct VFIODevice { >> bool needs_reset; >> bool no_mmap; >> bool ram_block_discard_allowed; >> - bool enable_migration; >> + OnOffAuto enable_migration; >> VFIODeviceOps *ops; >> unsigned int num_irqs; >> unsigned int num_regions; >> diff --git a/hw/vfio/migration.c b/hw/vfio/migration.c >> index 79eb81dfd7..d8e0848635 100644 >> --- a/hw/vfio/migration.c >> +++ b/hw/vfio/migration.c >> @@ -731,14 +731,6 @@ static int vfio_migration_query_flags(VFIODevice >> *vbasedev, uint64_t *mig_flags) >> feature->argsz = sizeof(buf); >> feature->flags = VFIO_DEVICE_FEATURE_GET | VFIO_DEVICE_FEATURE_MIGRATION; >> if (ioctl(vbasedev->fd, VFIO_DEVICE_FEATURE, feature)) { >> - if (errno == ENOTTY) { >> - error_report("%s: VFIO migration is not supported in kernel", >> - vbasedev->name); >> - } else { >> - error_report("%s: Failed to query VFIO migration support, err: %s", >> - vbasedev->name, strerror(errno)); >> - } >> - >> return -errno; >> } >> @@ -831,14 +823,28 @@ void vfio_reset_bytes_transferred(void) >> int vfio_migration_realize(VFIODevice *vbasedev, Error **errp) >> { >> - int ret = -ENOTSUP; >> + int ret; >> - if (!vbasedev->enable_migration) { >> + if (vbasedev->enable_migration == ON_OFF_AUTO_OFF) { >> + error_setg(&vbasedev->migration_blocker, >> + "%s: Migration is disabled for VFIO device", vbasedev->name); >> goto add_blocker; >> } >> ret = vfio_migration_init(vbasedev); >> if (ret) { > > It would be good to keep the message for 'errno == ENOTTY' as it was in > vfio_migration_query_flags(). When migration fails, it is an important > information to know that it is because the VFIO PCI host device driver > doesn't support the feature. The root cause could be deep below in FW or > how the VF was set up. > +1 As I have been in this rabbit hole >> + error_setg(&vbasedev->migration_blocker, >> + "%s: Migration couldn't be initialized for VFIO device, " >> + "err: %d (%s)", >> + vbasedev->name, ret, strerror(-ret)); >> + goto add_blocker; >> + } >> + >> + if (vbasedev->enable_migration == ON_OFF_AUTO_AUTO && >> + !vbasedev->dirty_pages_supported) { > > I don't agree with this test. > The alternative right now is perceptual dirty tracking. How is that OK as a default? It's not like we have even an option :( Maybe perhaps you refer to avoid strongly enforcing *always* it to allow testing of the non dirty tracking parts? Maybe when you 'force' enabling with enable-migration=on is when you ignore the dirty tracking which is what this is doing. >> + error_setg(&vbasedev->migration_blocker, >> + "%s: VFIO device doesn't support device dirty tracking", >> + vbasedev->name); >> goto add_blocker; >> } > I agree that with ON_OFF_AUTO_AUTO, errors at realize time should be recorded > in a migration blocker. What about the ON_OFF_AUTO_ON case ? If migration was > explicitly requested for the device and the conditions on the host are not met, > I think realize should fail and the machine abort. > +1 Good point > Thanks, > > C. > > > >> @@ -856,9 +862,6 @@ int vfio_migration_realize(VFIODevice *vbasedev, Error >> **errp) >> return 0; >> add_blocker: >> - error_setg(&vbasedev->migration_blocker, >> - "VFIO device doesn't support migration"); >> - >> ret = migrate_add_blocker(vbasedev->migration_blocker, errp); >> if (ret < 0) { >> error_free(vbasedev->migration_blocker); >> diff --git a/hw/vfio/pci.c b/hw/vfio/pci.c >> index 73874a94de..48584e3b01 100644 >> --- a/hw/vfio/pci.c >> +++ b/hw/vfio/pci.c >> @@ -3347,8 +3347,8 @@ static Property vfio_pci_dev_properties[] = { >> VFIO_FEATURE_ENABLE_REQ_BIT, true), >> DEFINE_PROP_BIT("x-igd-opregion", VFIOPCIDevice, features, >> VFIO_FEATURE_ENABLE_IGD_OPREGION_BIT, false), >> - DEFINE_PROP_BOOL("x-enable-migration", VFIOPCIDevice, >> - vbasedev.enable_migration, false), >> + DEFINE_PROP_ON_OFF_AUTO("enable-migration", VFIOPCIDevice, >> + vbasedev.enable_migration, ON_OFF_AUTO_AUTO), >> DEFINE_PROP_BOOL("x-no-mmap", VFIOPCIDevice, vbasedev.no_mmap, false), >> DEFINE_PROP_BOOL("x-balloon-allowed", VFIOPCIDevice, >> vbasedev.ram_block_discard_allowed, false), >
On 6/26/23 15:40, Joao Martins wrote: > On 26/06/2023 14:20, Cédric Le Goater wrote: >> Hello Avihai, >> >> On 6/26/23 10:23, Avihai Horon wrote: >>> The major parts of VFIO migration are supported today in QEMU. This >>> includes basic VFIO migration, device dirty page tracking and precopy >>> support. >>> >>> Thus, at this point in time, it seems appropriate to make VFIO migration >>> non-experimental: remove the x prefix from enable_migration property, >>> change it to ON_OFF_AUTO and let the default value be AUTO. >>> >>> In addition, make the following adjustments: >>> 1. Require device dirty tracking support when enable_migration is AUTO >>> (i.e., not explicitly enabled). This is because device dirty tracking >>> is currently the only method to do dirty page tracking, which is >>> essential for migrating in a reasonable downtime. >> >> hmm, I don't think QEMU should decide to disable a feature for all >> devices supposedly because it could be slow for some. That's too >> restrictive. What about devices with have small states ? for which >> the downtime would be reasonable even without device dirty tracking >> support. >> > > device dirty tracking refers to the ability to tracking dirty IOVA used by the > device which will DMA into RAM. It is required because the > consequence/alternative is to transfer all RAM in stop copy phase. Device state > size at that point is the least of our problems downtime wise. Arg. thanks for reminding me. I tend to take this for granted ... > I can imagine that allowing without dirty tracking is useful for developer > testing of the suspend/device-state flows, but as real default (auto) is very > questionable to let it go through without dirty tracking. When we have IOMMUFD > dirty tracking that's when we can relieve this restriction as a default. > > But then note that (...) > >> >>> Setting >>> enable_migration to ON will not require device dirty tracking. > > (...) this lets it ignore dirty tracking as you would like. > > >>> 2. Make migration blocker messages more elaborate. >>> 3. Remove error prints in vfio_migration_query_flags(). >>> 4. Remove a redundant assignment in vfio_migration_realize(). >>> >>> Signed-off-by: Avihai Horon <avihaih@nvidia.com> >>> --- >>> include/hw/vfio/vfio-common.h | 2 +- >>> hw/vfio/migration.c | 29 ++++++++++++++++------------- >>> hw/vfio/pci.c | 4 ++-- >>> 3 files changed, 19 insertions(+), 16 deletions(-) >>> >>> diff --git a/include/hw/vfio/vfio-common.h b/include/hw/vfio/vfio-common.h >>> index b4c28f318f..387eabde60 100644 >>> --- a/include/hw/vfio/vfio-common.h >>> +++ b/include/hw/vfio/vfio-common.h >>> @@ -139,7 +139,7 @@ typedef struct VFIODevice { >>> bool needs_reset; >>> bool no_mmap; >>> bool ram_block_discard_allowed; >>> - bool enable_migration; >>> + OnOffAuto enable_migration; >>> VFIODeviceOps *ops; >>> unsigned int num_irqs; >>> unsigned int num_regions; >>> diff --git a/hw/vfio/migration.c b/hw/vfio/migration.c >>> index 79eb81dfd7..d8e0848635 100644 >>> --- a/hw/vfio/migration.c >>> +++ b/hw/vfio/migration.c >>> @@ -731,14 +731,6 @@ static int vfio_migration_query_flags(VFIODevice >>> *vbasedev, uint64_t *mig_flags) >>> feature->argsz = sizeof(buf); >>> feature->flags = VFIO_DEVICE_FEATURE_GET | VFIO_DEVICE_FEATURE_MIGRATION; >>> if (ioctl(vbasedev->fd, VFIO_DEVICE_FEATURE, feature)) { >>> - if (errno == ENOTTY) { >>> - error_report("%s: VFIO migration is not supported in kernel", >>> - vbasedev->name); >>> - } else { >>> - error_report("%s: Failed to query VFIO migration support, err: %s", >>> - vbasedev->name, strerror(errno)); >>> - } >>> - >>> return -errno; >>> } >>> @@ -831,14 +823,28 @@ void vfio_reset_bytes_transferred(void) >>> int vfio_migration_realize(VFIODevice *vbasedev, Error **errp) >>> { >>> - int ret = -ENOTSUP; >>> + int ret; >>> - if (!vbasedev->enable_migration) { >>> + if (vbasedev->enable_migration == ON_OFF_AUTO_OFF) { >>> + error_setg(&vbasedev->migration_blocker, >>> + "%s: Migration is disabled for VFIO device", vbasedev->name); >>> goto add_blocker; >>> } >>> ret = vfio_migration_init(vbasedev); >>> if (ret) { >> >> It would be good to keep the message for 'errno == ENOTTY' as it was in >> vfio_migration_query_flags(). When migration fails, it is an important >> information to know that it is because the VFIO PCI host device driver >> doesn't support the feature. The root cause could be deep below in FW or >> how the VF was set up. >> > +1 As I have been in this rabbit hole > >>> + error_setg(&vbasedev->migration_blocker, >>> + "%s: Migration couldn't be initialized for VFIO device, " >>> + "err: %d (%s)", >>> + vbasedev->name, ret, strerror(-ret)); >>> + goto add_blocker; >>> + } >>> + >>> + if (vbasedev->enable_migration == ON_OFF_AUTO_AUTO && >>> + !vbasedev->dirty_pages_supported) { >> >> I don't agree with this test. >> > > The alternative right now is perceptual dirty tracking. How is that OK as a > default? It's not like we have even an option :( > > Maybe perhaps you refer to avoid strongly enforcing *always* it to allow testing > of the non dirty tracking parts? Maybe when you 'force' enabling with > enable-migration=on is when you ignore the dirty tracking which is what this is > doing. I see ON_OFF_AUTO_ON as a way to abort the machine startup while ON_OFF_AUTO_AUTO would let it run but block migration. We would need an extra property to relax the checks, else we are hijacking some pre-existing option to fit our need. Since dirty tracking is a must-have to implement migration support for any existing and future VFIO PCI variant driver, anything else would be experimental code and we are trying to remove the flag ! Please correct me if I am wrong. So, the case !vbasedev->dirty_pages_supported is just an extra information to report for why migration is not supported. Does that sound reasonable ? Thanks, C. > >>> + error_setg(&vbasedev->migration_blocker, >>> + "%s: VFIO device doesn't support device dirty tracking", >>> + vbasedev->name); >>> goto add_blocker; >>> } >> I agree that with ON_OFF_AUTO_AUTO, errors at realize time should be recorded >> in a migration blocker. What about the ON_OFF_AUTO_ON case ? If migration was >> explicitly requested for the device and the conditions on the host are not met, >> I think realize should fail and the machine abort. >> > +1 Good point > >> Thanks, >> >> C. >> >> >> >>> @@ -856,9 +862,6 @@ int vfio_migration_realize(VFIODevice *vbasedev, Error >>> **errp) >>> return 0; >>> add_blocker: >>> - error_setg(&vbasedev->migration_blocker, >>> - "VFIO device doesn't support migration"); >>> - >>> ret = migrate_add_blocker(vbasedev->migration_blocker, errp); >>> if (ret < 0) { >>> error_free(vbasedev->migration_blocker); >>> diff --git a/hw/vfio/pci.c b/hw/vfio/pci.c >>> index 73874a94de..48584e3b01 100644 >>> --- a/hw/vfio/pci.c >>> +++ b/hw/vfio/pci.c >>> @@ -3347,8 +3347,8 @@ static Property vfio_pci_dev_properties[] = { >>> VFIO_FEATURE_ENABLE_REQ_BIT, true), >>> DEFINE_PROP_BIT("x-igd-opregion", VFIOPCIDevice, features, >>> VFIO_FEATURE_ENABLE_IGD_OPREGION_BIT, false), >>> - DEFINE_PROP_BOOL("x-enable-migration", VFIOPCIDevice, >>> - vbasedev.enable_migration, false), >>> + DEFINE_PROP_ON_OFF_AUTO("enable-migration", VFIOPCIDevice, >>> + vbasedev.enable_migration, ON_OFF_AUTO_AUTO), >>> DEFINE_PROP_BOOL("x-no-mmap", VFIOPCIDevice, vbasedev.no_mmap, false), >>> DEFINE_PROP_BOOL("x-balloon-allowed", VFIOPCIDevice, >>> vbasedev.ram_block_discard_allowed, false), >>
On Mon, Jun 26, 2023 at 05:26:42PM +0200, Cédric Le Goater wrote: > Since dirty tracking is a must-have to implement migration support > for any existing and future VFIO PCI variant driver, anything else > would be experimental code and we are trying to remove the flag ! > Please correct me if I am wrong. I don't think we should call it experimental - it is like other qemu options where we can choose to run qemu in a suboptimal way. Jason
On 26/06/2023 16:26, Cédric Le Goater wrote: > On 6/26/23 15:40, Joao Martins wrote: >> On 26/06/2023 14:20, Cédric Le Goater wrote: >>> On 6/26/23 10:23, Avihai Horon wrote: >>>> + error_setg(&vbasedev->migration_blocker, >>>> + "%s: Migration couldn't be initialized for VFIO device, " >>>> + "err: %d (%s)", >>>> + vbasedev->name, ret, strerror(-ret)); >>>> + goto add_blocker; >>>> + } >>>> + >>>> + if (vbasedev->enable_migration == ON_OFF_AUTO_AUTO && >>>> + !vbasedev->dirty_pages_supported) { >>> >>> I don't agree with this test. >>> >> >> The alternative right now is perceptual dirty tracking. How is that OK as a >> default? It's not like we have even an option :( >> >> Maybe perhaps you refer to avoid strongly enforcing *always* it to allow testing >> of the non dirty tracking parts? Maybe when you 'force' enabling with >> enable-migration=on is when you ignore the dirty tracking which is what this is >> doing. > > > I see ON_OFF_AUTO_ON as a way to abort the machine startup while > ON_OFF_AUTO_AUTO would let it run but block migration. We would > need an extra property to relax the checks, else we are hijacking > some pre-existing option to fit our need. > OK > Since dirty tracking is a must-have to implement migration support > for any existing and future VFIO PCI variant driver, anything else > would be experimental code and we are trying to remove the flag ! > Please correct me if I am wrong. > My thinking was mainly requiring the default migration case without any relaxing from the user to require dirty tracking by default. hisilicon driver is the current vfio driver upstream that doesn't support dirty tracking (neither P2P). > So, the case !vbasedev->dirty_pages_supported is just an extra > information to report for why migration is not supported. Does > that sound reasonable ? > We can always piggy back on the x-pre-copy-dirty-page-tracking (which already exists too) as means to relax this option, and that should cover this other case. My comment was more targetted at your suggestion of making it optional *by default* to not use the dirty tracking. Joao
On 6/26/23 18:19, Jason Gunthorpe wrote: > On Mon, Jun 26, 2023 at 05:26:42PM +0200, Cédric Le Goater wrote: > >> Since dirty tracking is a must-have to implement migration support >> for any existing and future VFIO PCI variant driver, anything else >> would be experimental code and we are trying to remove the flag ! >> Please correct me if I am wrong. > > I don't think we should call it experimental - it is like other qemu > options where we can choose to run qemu in a suboptimal way. In that case, whether the driver implements dirty tracking or not is not a condition to enable migration, only the host kernel driver support is. C.
On Mon, 26 Jun 2023 17:26:42 +0200 Cédric Le Goater <clg@redhat.com> wrote: > On 6/26/23 15:40, Joao Martins wrote: > > On 26/06/2023 14:20, Cédric Le Goater wrote: > >> Hello Avihai, > >> > >> On 6/26/23 10:23, Avihai Horon wrote: > >>> The major parts of VFIO migration are supported today in QEMU. This > >>> includes basic VFIO migration, device dirty page tracking and precopy > >>> support. > >>> > >>> Thus, at this point in time, it seems appropriate to make VFIO migration > >>> non-experimental: remove the x prefix from enable_migration property, > >>> change it to ON_OFF_AUTO and let the default value be AUTO. > >>> > >>> In addition, make the following adjustments: > >>> 1. Require device dirty tracking support when enable_migration is AUTO > >>> (i.e., not explicitly enabled). This is because device dirty tracking > >>> is currently the only method to do dirty page tracking, which is > >>> essential for migrating in a reasonable downtime. > >> > >> hmm, I don't think QEMU should decide to disable a feature for all > >> devices supposedly because it could be slow for some. That's too > >> restrictive. What about devices with have small states ? for which > >> the downtime would be reasonable even without device dirty tracking > >> support. > >> > > > > device dirty tracking refers to the ability to tracking dirty IOVA used by the > > device which will DMA into RAM. It is required because the > > consequence/alternative is to transfer all RAM in stop copy phase. Device state > > size at that point is the least of our problems downtime wise. > > Arg. thanks for reminding me. I tend to take this for granted ... My initial reaction was the same, for instance we could have a non-DMA device (ex. PCI serial card) that supports migration w/o dirty tracking, but QEMU cannot assume the device doesn't do DMA, nor is it worth our time to monitor whether bus-master is ever enabled for the device, so QEMU needs to assume all memory that's DMA accessible for the device is perpetually dirty. Also, if such a corner case existed for a non-DMA migratable device, the easier path is simply to require dirty tracking stubs in the variant driver to report no memory dirtied. > > I can imagine that allowing without dirty tracking is useful for developer > > testing of the suspend/device-state flows, but as real default (auto) is very > > questionable to let it go through without dirty tracking. When we have IOMMUFD > > dirty tracking that's when we can relieve this restriction as a default. > > > > But then note that (...) > > > >> > >>> Setting > >>> enable_migration to ON will not require device dirty tracking. > > > > (...) this lets it ignore dirty tracking as you would like. > > > > > >>> 2. Make migration blocker messages more elaborate. > >>> 3. Remove error prints in vfio_migration_query_flags(). > >>> 4. Remove a redundant assignment in vfio_migration_realize(). > >>> > >>> Signed-off-by: Avihai Horon <avihaih@nvidia.com> > >>> --- > >>> include/hw/vfio/vfio-common.h | 2 +- > >>> hw/vfio/migration.c | 29 ++++++++++++++++------------- > >>> hw/vfio/pci.c | 4 ++-- > >>> 3 files changed, 19 insertions(+), 16 deletions(-) > >>> > >>> diff --git a/include/hw/vfio/vfio-common.h b/include/hw/vfio/vfio-common.h > >>> index b4c28f318f..387eabde60 100644 > >>> --- a/include/hw/vfio/vfio-common.h > >>> +++ b/include/hw/vfio/vfio-common.h > >>> @@ -139,7 +139,7 @@ typedef struct VFIODevice { > >>> bool needs_reset; > >>> bool no_mmap; > >>> bool ram_block_discard_allowed; > >>> - bool enable_migration; > >>> + OnOffAuto enable_migration; > >>> VFIODeviceOps *ops; > >>> unsigned int num_irqs; > >>> unsigned int num_regions; > >>> diff --git a/hw/vfio/migration.c b/hw/vfio/migration.c > >>> index 79eb81dfd7..d8e0848635 100644 > >>> --- a/hw/vfio/migration.c > >>> +++ b/hw/vfio/migration.c > >>> @@ -731,14 +731,6 @@ static int vfio_migration_query_flags(VFIODevice > >>> *vbasedev, uint64_t *mig_flags) > >>> feature->argsz = sizeof(buf); > >>> feature->flags = VFIO_DEVICE_FEATURE_GET | VFIO_DEVICE_FEATURE_MIGRATION; > >>> if (ioctl(vbasedev->fd, VFIO_DEVICE_FEATURE, feature)) { > >>> - if (errno == ENOTTY) { > >>> - error_report("%s: VFIO migration is not supported in kernel", > >>> - vbasedev->name); > >>> - } else { > >>> - error_report("%s: Failed to query VFIO migration support, err: %s", > >>> - vbasedev->name, strerror(errno)); > >>> - } > >>> - > >>> return -errno; > >>> } > >>> @@ -831,14 +823,28 @@ void vfio_reset_bytes_transferred(void) > >>> int vfio_migration_realize(VFIODevice *vbasedev, Error **errp) > >>> { > >>> - int ret = -ENOTSUP; > >>> + int ret; > >>> - if (!vbasedev->enable_migration) { > >>> + if (vbasedev->enable_migration == ON_OFF_AUTO_OFF) { > >>> + error_setg(&vbasedev->migration_blocker, > >>> + "%s: Migration is disabled for VFIO device", vbasedev->name); > >>> goto add_blocker; > >>> } > >>> ret = vfio_migration_init(vbasedev); > >>> if (ret) { > >> > >> It would be good to keep the message for 'errno == ENOTTY' as it was in > >> vfio_migration_query_flags(). When migration fails, it is an important > >> information to know that it is because the VFIO PCI host device driver > >> doesn't support the feature. The root cause could be deep below in FW or > >> how the VF was set up. > >> > > +1 As I have been in this rabbit hole > > > >>> + error_setg(&vbasedev->migration_blocker, > >>> + "%s: Migration couldn't be initialized for VFIO device, " > >>> + "err: %d (%s)", > >>> + vbasedev->name, ret, strerror(-ret)); > >>> + goto add_blocker; > >>> + } > >>> + > >>> + if (vbasedev->enable_migration == ON_OFF_AUTO_AUTO && > >>> + !vbasedev->dirty_pages_supported) { > >> > >> I don't agree with this test. > >> > > > > The alternative right now is perceptual dirty tracking. How is that OK as a > > default? It's not like we have even an option :( > > > > Maybe perhaps you refer to avoid strongly enforcing *always* it to allow testing > > of the non dirty tracking parts? Maybe when you 'force' enabling with > > enable-migration=on is when you ignore the dirty tracking which is what this is > > doing. > > > I see ON_OFF_AUTO_ON as a way to abort the machine startup while > ON_OFF_AUTO_AUTO would let it run but block migration. Agreed. There's a little bit of redundancy between the device-level "enable-migration=on" option and the global "-only-migratable" option relative to preventing machine startup, but it also doesn't make sense to me if the device-level option let realize complete successfully if the device doesn't support or fails migration setup. So I think we'd generally rely on using the -only-migratable option with the default ON_OFF_AUTO_AUTO value, allow the ON_OFF_AUTO_ON value to enable dis-recommended support, and live with the redundancy that it should also cause the device realize to fail if migration is not supported. Thanks, Alex > We would > need an extra property to relax the checks, else we are hijacking > some pre-existing option to fit our need. > > Since dirty tracking is a must-have to implement migration support > for any existing and future VFIO PCI variant driver, anything else > would be experimental code and we are trying to remove the flag ! > Please correct me if I am wrong. > > So, the case !vbasedev->dirty_pages_supported is just an extra > information to report for why migration is not supported. Does > that sound reasonable ? > > Thanks, > > C. > > > > > > >>> + error_setg(&vbasedev->migration_blocker, > >>> + "%s: VFIO device doesn't support device dirty tracking", > >>> + vbasedev->name); > >>> goto add_blocker; > >>> } > >> I agree that with ON_OFF_AUTO_AUTO, errors at realize time should be recorded > >> in a migration blocker. What about the ON_OFF_AUTO_ON case ? If migration was > >> explicitly requested for the device and the conditions on the host are not met, > >> I think realize should fail and the machine abort. > >> > > +1 Good point > > > >> Thanks, > >> > >> C. > >> > >> > >> > >>> @@ -856,9 +862,6 @@ int vfio_migration_realize(VFIODevice *vbasedev, Error > >>> **errp) > >>> return 0; > >>> add_blocker: > >>> - error_setg(&vbasedev->migration_blocker, > >>> - "VFIO device doesn't support migration"); > >>> - > >>> ret = migrate_add_blocker(vbasedev->migration_blocker, errp); > >>> if (ret < 0) { > >>> error_free(vbasedev->migration_blocker); > >>> diff --git a/hw/vfio/pci.c b/hw/vfio/pci.c > >>> index 73874a94de..48584e3b01 100644 > >>> --- a/hw/vfio/pci.c > >>> +++ b/hw/vfio/pci.c > >>> @@ -3347,8 +3347,8 @@ static Property vfio_pci_dev_properties[] = { > >>> VFIO_FEATURE_ENABLE_REQ_BIT, true), > >>> DEFINE_PROP_BIT("x-igd-opregion", VFIOPCIDevice, features, > >>> VFIO_FEATURE_ENABLE_IGD_OPREGION_BIT, false), > >>> - DEFINE_PROP_BOOL("x-enable-migration", VFIOPCIDevice, > >>> - vbasedev.enable_migration, false), > >>> + DEFINE_PROP_ON_OFF_AUTO("enable-migration", VFIOPCIDevice, > >>> + vbasedev.enable_migration, ON_OFF_AUTO_AUTO), > >>> DEFINE_PROP_BOOL("x-no-mmap", VFIOPCIDevice, vbasedev.no_mmap, false), > >>> DEFINE_PROP_BOOL("x-balloon-allowed", VFIOPCIDevice, > >>> vbasedev.ram_block_discard_allowed, false), > >> >
On 26/06/2023 20:27, Alex Williamson wrote: > External email: Use caution opening links or attachments > > > On Mon, 26 Jun 2023 17:26:42 +0200 > Cédric Le Goater <clg@redhat.com> wrote: > >> On 6/26/23 15:40, Joao Martins wrote: >>> On 26/06/2023 14:20, Cédric Le Goater wrote: >>>> Hello Avihai, >>>> >>>> On 6/26/23 10:23, Avihai Horon wrote: >>>>> The major parts of VFIO migration are supported today in QEMU. This >>>>> includes basic VFIO migration, device dirty page tracking and precopy >>>>> support. >>>>> >>>>> Thus, at this point in time, it seems appropriate to make VFIO migration >>>>> non-experimental: remove the x prefix from enable_migration property, >>>>> change it to ON_OFF_AUTO and let the default value be AUTO. >>>>> >>>>> In addition, make the following adjustments: >>>>> 1. Require device dirty tracking support when enable_migration is AUTO >>>>> (i.e., not explicitly enabled). This is because device dirty tracking >>>>> is currently the only method to do dirty page tracking, which is >>>>> essential for migrating in a reasonable downtime. >>>> hmm, I don't think QEMU should decide to disable a feature for all >>>> devices supposedly because it could be slow for some. That's too >>>> restrictive. What about devices with have small states ? for which >>>> the downtime would be reasonable even without device dirty tracking >>>> support. >>>> >>> device dirty tracking refers to the ability to tracking dirty IOVA used by the >>> device which will DMA into RAM. It is required because the >>> consequence/alternative is to transfer all RAM in stop copy phase. Device state >>> size at that point is the least of our problems downtime wise. >> Arg. thanks for reminding me. I tend to take this for granted ... > My initial reaction was the same, for instance we could have a non-DMA > device (ex. PCI serial card) that supports migration w/o dirty > tracking, but QEMU cannot assume the device doesn't do DMA, nor is it > worth our time to monitor whether bus-master is ever enabled for the > device, so QEMU needs to assume all memory that's DMA accessible for > the device is perpetually dirty. Also, if such a corner case existed > for a non-DMA migratable device, the easier path is simply to require > dirty tracking stubs in the variant driver to report no memory dirtied. > >>> I can imagine that allowing without dirty tracking is useful for developer >>> testing of the suspend/device-state flows, but as real default (auto) is very >>> questionable to let it go through without dirty tracking. When we have IOMMUFD >>> dirty tracking that's when we can relieve this restriction as a default. >>> >>> But then note that (...) >>> >>>>> Setting >>>>> enable_migration to ON will not require device dirty tracking. >>> (...) this lets it ignore dirty tracking as you would like. >>> >>> >>>>> 2. Make migration blocker messages more elaborate. >>>>> 3. Remove error prints in vfio_migration_query_flags(). >>>>> 4. Remove a redundant assignment in vfio_migration_realize(). >>>>> >>>>> Signed-off-by: Avihai Horon <avihaih@nvidia.com> >>>>> --- >>>>> include/hw/vfio/vfio-common.h | 2 +- >>>>> hw/vfio/migration.c | 29 ++++++++++++++++------------- >>>>> hw/vfio/pci.c | 4 ++-- >>>>> 3 files changed, 19 insertions(+), 16 deletions(-) >>>>> >>>>> diff --git a/include/hw/vfio/vfio-common.h b/include/hw/vfio/vfio-common.h >>>>> index b4c28f318f..387eabde60 100644 >>>>> --- a/include/hw/vfio/vfio-common.h >>>>> +++ b/include/hw/vfio/vfio-common.h >>>>> @@ -139,7 +139,7 @@ typedef struct VFIODevice { >>>>> bool needs_reset; >>>>> bool no_mmap; >>>>> bool ram_block_discard_allowed; >>>>> - bool enable_migration; >>>>> + OnOffAuto enable_migration; >>>>> VFIODeviceOps *ops; >>>>> unsigned int num_irqs; >>>>> unsigned int num_regions; >>>>> diff --git a/hw/vfio/migration.c b/hw/vfio/migration.c >>>>> index 79eb81dfd7..d8e0848635 100644 >>>>> --- a/hw/vfio/migration.c >>>>> +++ b/hw/vfio/migration.c >>>>> @@ -731,14 +731,6 @@ static int vfio_migration_query_flags(VFIODevice >>>>> *vbasedev, uint64_t *mig_flags) >>>>> feature->argsz = sizeof(buf); >>>>> feature->flags = VFIO_DEVICE_FEATURE_GET | VFIO_DEVICE_FEATURE_MIGRATION; >>>>> if (ioctl(vbasedev->fd, VFIO_DEVICE_FEATURE, feature)) { >>>>> - if (errno == ENOTTY) { >>>>> - error_report("%s: VFIO migration is not supported in kernel", >>>>> - vbasedev->name); >>>>> - } else { >>>>> - error_report("%s: Failed to query VFIO migration support, err: %s", >>>>> - vbasedev->name, strerror(errno)); >>>>> - } >>>>> - >>>>> return -errno; >>>>> } >>>>> @@ -831,14 +823,28 @@ void vfio_reset_bytes_transferred(void) >>>>> int vfio_migration_realize(VFIODevice *vbasedev, Error **errp) >>>>> { >>>>> - int ret = -ENOTSUP; >>>>> + int ret; >>>>> - if (!vbasedev->enable_migration) { >>>>> + if (vbasedev->enable_migration == ON_OFF_AUTO_OFF) { >>>>> + error_setg(&vbasedev->migration_blocker, >>>>> + "%s: Migration is disabled for VFIO device", vbasedev->name); >>>>> goto add_blocker; >>>>> } >>>>> ret = vfio_migration_init(vbasedev); >>>>> if (ret) { >>>> It would be good to keep the message for 'errno == ENOTTY' as it was in >>>> vfio_migration_query_flags(). When migration fails, it is an important >>>> information to know that it is because the VFIO PCI host device driver >>>> doesn't support the feature. The root cause could be deep below in FW or >>>> how the VF was set up. >>>> >>> +1 As I have been in this rabbit hole Sure, I will add it. >>> >>>>> + error_setg(&vbasedev->migration_blocker, >>>>> + "%s: Migration couldn't be initialized for VFIO device, " >>>>> + "err: %d (%s)", >>>>> + vbasedev->name, ret, strerror(-ret)); >>>>> + goto add_blocker; >>>>> + } >>>>> + >>>>> + if (vbasedev->enable_migration == ON_OFF_AUTO_AUTO && >>>>> + !vbasedev->dirty_pages_supported) { >>>> I don't agree with this test. >>>> >>> The alternative right now is perceptual dirty tracking. How is that OK as a >>> default? It's not like we have even an option :( >>> >>> Maybe perhaps you refer to avoid strongly enforcing *always* it to allow testing >>> of the non dirty tracking parts? Maybe when you 'force' enabling with >>> enable-migration=on is when you ignore the dirty tracking which is what this is >>> doing. >> >> I see ON_OFF_AUTO_ON as a way to abort the machine startup while >> ON_OFF_AUTO_AUTO would let it run but block migration. > Agreed. There's a little bit of redundancy between the device-level > "enable-migration=on" option and the global "-only-migratable" option > relative to preventing machine startup, but it also doesn't make sense > to me if the device-level option let realize complete successfully if > the device doesn't support or fails migration setup. So I think we'd > generally rely on using the -only-migratable option with the default > ON_OFF_AUTO_AUTO value, allow the ON_OFF_AUTO_ON value to enable > dis-recommended support, and live with the redundancy that it should > also cause the device realize to fail if migration is not supported. > Thanks, > > Alex OK. When enable_migration=AUTO we allow blockers. When enable_migration=ON we don't allow blockers and instead prevent realization of VFIO device. Regarding device dirty tracking, we keep current behavior, right? That is: When enable_migration=AUTO we block migration if device dirty tracking is not supported. When enable_migration=ON we allow migration even if device dirty tracking is not supported (in which case DMA-able memory will be perpetually dirtied). Thanks. > >> We would >> need an extra property to relax the checks, else we are hijacking >> some pre-existing option to fit our need. >> >> Since dirty tracking is a must-have to implement migration support >> for any existing and future VFIO PCI variant driver, anything else >> would be experimental code and we are trying to remove the flag ! >> Please correct me if I am wrong. >> >> So, the case !vbasedev->dirty_pages_supported is just an extra >> information to report for why migration is not supported. Does >> that sound reasonable ? >> >> Thanks, >> >> C. >> >> >> >>>>> + error_setg(&vbasedev->migration_blocker, >>>>> + "%s: VFIO device doesn't support device dirty tracking", >>>>> + vbasedev->name); >>>>> goto add_blocker; >>>>> } >>>> I agree that with ON_OFF_AUTO_AUTO, errors at realize time should be recorded >>>> in a migration blocker. What about the ON_OFF_AUTO_ON case ? If migration was >>>> explicitly requested for the device and the conditions on the host are not met, >>>> I think realize should fail and the machine abort. >>>> >>> +1 Good point >>> >>>> Thanks, >>>> >>>> C. >>>> >>>> >>>> >>>>> @@ -856,9 +862,6 @@ int vfio_migration_realize(VFIODevice *vbasedev, Error >>>>> **errp) >>>>> return 0; >>>>> add_blocker: >>>>> - error_setg(&vbasedev->migration_blocker, >>>>> - "VFIO device doesn't support migration"); >>>>> - >>>>> ret = migrate_add_blocker(vbasedev->migration_blocker, errp); >>>>> if (ret < 0) { >>>>> error_free(vbasedev->migration_blocker); >>>>> diff --git a/hw/vfio/pci.c b/hw/vfio/pci.c >>>>> index 73874a94de..48584e3b01 100644 >>>>> --- a/hw/vfio/pci.c >>>>> +++ b/hw/vfio/pci.c >>>>> @@ -3347,8 +3347,8 @@ static Property vfio_pci_dev_properties[] = { >>>>> VFIO_FEATURE_ENABLE_REQ_BIT, true), >>>>> DEFINE_PROP_BIT("x-igd-opregion", VFIOPCIDevice, features, >>>>> VFIO_FEATURE_ENABLE_IGD_OPREGION_BIT, false), >>>>> - DEFINE_PROP_BOOL("x-enable-migration", VFIOPCIDevice, >>>>> - vbasedev.enable_migration, false), >>>>> + DEFINE_PROP_ON_OFF_AUTO("enable-migration", VFIOPCIDevice, >>>>> + vbasedev.enable_migration, ON_OFF_AUTO_AUTO), >>>>> DEFINE_PROP_BOOL("x-no-mmap", VFIOPCIDevice, vbasedev.no_mmap, false), >>>>> DEFINE_PROP_BOOL("x-balloon-allowed", VFIOPCIDevice, >>>>> vbasedev.ram_block_discard_allowed, false),
[ Cc: Shameer ] >>> I see ON_OFF_AUTO_ON as a way to abort the machine startup while >>> ON_OFF_AUTO_AUTO would let it run but block migration. >> >> Agreed. There's a little bit of redundancy between the device-level >> "enable-migration=on" option and the global "-only-migratable" option >> relative to preventing machine startup, but it also doesn't make sense >> to me if the device-level option let realize complete successfully if >> the device doesn't support or fails migration setup. So I think we'd >> generally rely on using the -only-migratable option with the default >> ON_OFF_AUTO_AUTO value, allow the ON_OFF_AUTO_ON value to enable >> dis-recommended support, and live with the redundancy that it should >> also cause the device realize to fail if migration is not supported. >> Thanks, >> >> Alex > > OK. > > When enable_migration=AUTO we allow blockers. > When enable_migration=ON we don't allow blockers and instead prevent realization of VFIO device. > > Regarding device dirty tracking, we keep current behavior, right? > That is: > When enable_migration=AUTO we block migration if device dirty tracking is not supported. > When enable_migration=ON we allow migration even if device dirty tracking is not supported > (in which case DMA-able memory will be perpetually dirtied). Yes. That's how I understand it. This is what you initially proposed. The default behavior is to allow migration only if the host kernel driver supports dirty tracking. We have a way to run and migrate a machine with a device not supporting dirty tracking. Only Hisilicon is in that case today. May be there are plans to add dirty tracking support ? Thanks, C.
On Tue, Jun 27, 2023 at 02:21:55PM +0200, Cédric Le Goater wrote: > We have a way to run and migrate a machine with a device not supporting > dirty tracking. Only Hisilicon is in that case today. May be there are > plans to add dirty tracking support ? Hisilicon will eventually use Joao's work for IOMMU based tracking, this is what their HW was designed to do. Jason
On Tue, 27 Jun 2023 11:00:46 +0300 Avihai Horon <avihaih@nvidia.com> wrote: > On 26/06/2023 20:27, Alex Williamson wrote: > > External email: Use caution opening links or attachments > > > > > > On Mon, 26 Jun 2023 17:26:42 +0200 > > Cédric Le Goater <clg@redhat.com> wrote: > > > >> On 6/26/23 15:40, Joao Martins wrote: > >>> On 26/06/2023 14:20, Cédric Le Goater wrote: > >>>> Hello Avihai, > >>>> > >>>> On 6/26/23 10:23, Avihai Horon wrote: > >>>>> The major parts of VFIO migration are supported today in QEMU. This > >>>>> includes basic VFIO migration, device dirty page tracking and precopy > >>>>> support. > >>>>> > >>>>> Thus, at this point in time, it seems appropriate to make VFIO migration > >>>>> non-experimental: remove the x prefix from enable_migration property, > >>>>> change it to ON_OFF_AUTO and let the default value be AUTO. > >>>>> > >>>>> In addition, make the following adjustments: > >>>>> 1. Require device dirty tracking support when enable_migration is AUTO > >>>>> (i.e., not explicitly enabled). This is because device dirty tracking > >>>>> is currently the only method to do dirty page tracking, which is > >>>>> essential for migrating in a reasonable downtime. > >>>> hmm, I don't think QEMU should decide to disable a feature for all > >>>> devices supposedly because it could be slow for some. That's too > >>>> restrictive. What about devices with have small states ? for which > >>>> the downtime would be reasonable even without device dirty tracking > >>>> support. > >>>> > >>> device dirty tracking refers to the ability to tracking dirty IOVA used by the > >>> device which will DMA into RAM. It is required because the > >>> consequence/alternative is to transfer all RAM in stop copy phase. Device state > >>> size at that point is the least of our problems downtime wise. > >> Arg. thanks for reminding me. I tend to take this for granted ... > > My initial reaction was the same, for instance we could have a non-DMA > > device (ex. PCI serial card) that supports migration w/o dirty > > tracking, but QEMU cannot assume the device doesn't do DMA, nor is it > > worth our time to monitor whether bus-master is ever enabled for the > > device, so QEMU needs to assume all memory that's DMA accessible for > > the device is perpetually dirty. Also, if such a corner case existed > > for a non-DMA migratable device, the easier path is simply to require > > dirty tracking stubs in the variant driver to report no memory dirtied. > > > >>> I can imagine that allowing without dirty tracking is useful for developer > >>> testing of the suspend/device-state flows, but as real default (auto) is very > >>> questionable to let it go through without dirty tracking. When we have IOMMUFD > >>> dirty tracking that's when we can relieve this restriction as a default. > >>> > >>> But then note that (...) > >>> > >>>>> Setting > >>>>> enable_migration to ON will not require device dirty tracking. > >>> (...) this lets it ignore dirty tracking as you would like. > >>> > >>> > >>>>> 2. Make migration blocker messages more elaborate. > >>>>> 3. Remove error prints in vfio_migration_query_flags(). > >>>>> 4. Remove a redundant assignment in vfio_migration_realize(). > >>>>> > >>>>> Signed-off-by: Avihai Horon <avihaih@nvidia.com> > >>>>> --- > >>>>> include/hw/vfio/vfio-common.h | 2 +- > >>>>> hw/vfio/migration.c | 29 ++++++++++++++++------------- > >>>>> hw/vfio/pci.c | 4 ++-- > >>>>> 3 files changed, 19 insertions(+), 16 deletions(-) > >>>>> > >>>>> diff --git a/include/hw/vfio/vfio-common.h b/include/hw/vfio/vfio-common.h > >>>>> index b4c28f318f..387eabde60 100644 > >>>>> --- a/include/hw/vfio/vfio-common.h > >>>>> +++ b/include/hw/vfio/vfio-common.h > >>>>> @@ -139,7 +139,7 @@ typedef struct VFIODevice { > >>>>> bool needs_reset; > >>>>> bool no_mmap; > >>>>> bool ram_block_discard_allowed; > >>>>> - bool enable_migration; > >>>>> + OnOffAuto enable_migration; > >>>>> VFIODeviceOps *ops; > >>>>> unsigned int num_irqs; > >>>>> unsigned int num_regions; > >>>>> diff --git a/hw/vfio/migration.c b/hw/vfio/migration.c > >>>>> index 79eb81dfd7..d8e0848635 100644 > >>>>> --- a/hw/vfio/migration.c > >>>>> +++ b/hw/vfio/migration.c > >>>>> @@ -731,14 +731,6 @@ static int vfio_migration_query_flags(VFIODevice > >>>>> *vbasedev, uint64_t *mig_flags) > >>>>> feature->argsz = sizeof(buf); > >>>>> feature->flags = VFIO_DEVICE_FEATURE_GET | VFIO_DEVICE_FEATURE_MIGRATION; > >>>>> if (ioctl(vbasedev->fd, VFIO_DEVICE_FEATURE, feature)) { > >>>>> - if (errno == ENOTTY) { > >>>>> - error_report("%s: VFIO migration is not supported in kernel", > >>>>> - vbasedev->name); > >>>>> - } else { > >>>>> - error_report("%s: Failed to query VFIO migration support, err: %s", > >>>>> - vbasedev->name, strerror(errno)); > >>>>> - } > >>>>> - > >>>>> return -errno; > >>>>> } > >>>>> @@ -831,14 +823,28 @@ void vfio_reset_bytes_transferred(void) > >>>>> int vfio_migration_realize(VFIODevice *vbasedev, Error **errp) > >>>>> { > >>>>> - int ret = -ENOTSUP; > >>>>> + int ret; > >>>>> - if (!vbasedev->enable_migration) { > >>>>> + if (vbasedev->enable_migration == ON_OFF_AUTO_OFF) { > >>>>> + error_setg(&vbasedev->migration_blocker, > >>>>> + "%s: Migration is disabled for VFIO device", vbasedev->name); > >>>>> goto add_blocker; > >>>>> } > >>>>> ret = vfio_migration_init(vbasedev); > >>>>> if (ret) { > >>>> It would be good to keep the message for 'errno == ENOTTY' as it was in > >>>> vfio_migration_query_flags(). When migration fails, it is an important > >>>> information to know that it is because the VFIO PCI host device driver > >>>> doesn't support the feature. The root cause could be deep below in FW or > >>>> how the VF was set up. > >>>> > >>> +1 As I have been in this rabbit hole > > Sure, I will add it. > > >>> > >>>>> + error_setg(&vbasedev->migration_blocker, > >>>>> + "%s: Migration couldn't be initialized for VFIO device, " > >>>>> + "err: %d (%s)", > >>>>> + vbasedev->name, ret, strerror(-ret)); > >>>>> + goto add_blocker; > >>>>> + } > >>>>> + > >>>>> + if (vbasedev->enable_migration == ON_OFF_AUTO_AUTO && > >>>>> + !vbasedev->dirty_pages_supported) { > >>>> I don't agree with this test. > >>>> > >>> The alternative right now is perceptual dirty tracking. How is that OK as a > >>> default? It's not like we have even an option :( > >>> > >>> Maybe perhaps you refer to avoid strongly enforcing *always* it to allow testing > >>> of the non dirty tracking parts? Maybe when you 'force' enabling with > >>> enable-migration=on is when you ignore the dirty tracking which is what this is > >>> doing. > >> > >> I see ON_OFF_AUTO_ON as a way to abort the machine startup while > >> ON_OFF_AUTO_AUTO would let it run but block migration. > > Agreed. There's a little bit of redundancy between the device-level > > "enable-migration=on" option and the global "-only-migratable" option > > relative to preventing machine startup, but it also doesn't make sense > > to me if the device-level option let realize complete successfully if > > the device doesn't support or fails migration setup. So I think we'd > > generally rely on using the -only-migratable option with the default > > ON_OFF_AUTO_AUTO value, allow the ON_OFF_AUTO_ON value to enable > > dis-recommended support, and live with the redundancy that it should > > also cause the device realize to fail if migration is not supported. > > Thanks, > > > > Alex > > OK. > > When enable_migration=AUTO we allow blockers. > When enable_migration=ON we don't allow blockers and instead prevent > realization of VFIO device. > > Regarding device dirty tracking, we keep current behavior, right? > That is: > When enable_migration=AUTO we block migration if device dirty tracking > is not supported. > When enable_migration=ON we allow migration even if device dirty > tracking is not supported (in which case DMA-able memory will be > perpetually dirtied). Yes, and I think we'd be justified in logging a warning when migration is enabled without any dirty page tracking support. Thanks, Alex
> -----Original Message----- > From: Jason Gunthorpe [mailto:jgg@nvidia.com] > Sent: 27 June 2023 13:30 > To: Cédric Le Goater <clg@redhat.com> > Cc: Avihai Horon <avihaih@nvidia.com>; Alex Williamson > <alex.williamson@redhat.com>; Joao Martins <joao.m.martins@oracle.com>; > Juan Quintela <quintela@redhat.com>; Peter Xu <peterx@redhat.com>; > Leonardo Bras <leobras@redhat.com>; Zhenzhong Duan > <zhenzhong.duan@intel.com>; Yishai Hadas <yishaih@nvidia.com>; Maor > Gottlieb <maorg@nvidia.com>; Kirti Wankhede <kwankhede@nvidia.com>; > Tarun Gupta <targupta@nvidia.com>; qemu-devel@nongnu.org; Shameerali > Kolothum Thodi <shameerali.kolothum.thodi@huawei.com> > Subject: Re: [PATCH 3/3] vfio/migration: Make VFIO migration > non-experimental > > On Tue, Jun 27, 2023 at 02:21:55PM +0200, Cédric Le Goater wrote: > > > We have a way to run and migrate a machine with a device not supporting > > dirty tracking. Only Hisilicon is in that case today. May be there are > > plans to add dirty tracking support ? > > Hisilicon will eventually use Joao's work for IOMMU based tracking, > this is what their HW was designed to do. Yes. The plan is to make use of SMMUv3 HTTU feature for dirty tracking based on Joao's work here, https://lore.kernel.org/kvm/20230518204650.14541-1-joao.m.martins@oracle.com/ Thanks, Shameer
diff --git a/include/hw/vfio/vfio-common.h b/include/hw/vfio/vfio-common.h index b4c28f318f..387eabde60 100644 --- a/include/hw/vfio/vfio-common.h +++ b/include/hw/vfio/vfio-common.h @@ -139,7 +139,7 @@ typedef struct VFIODevice { bool needs_reset; bool no_mmap; bool ram_block_discard_allowed; - bool enable_migration; + OnOffAuto enable_migration; VFIODeviceOps *ops; unsigned int num_irqs; unsigned int num_regions; diff --git a/hw/vfio/migration.c b/hw/vfio/migration.c index 79eb81dfd7..d8e0848635 100644 --- a/hw/vfio/migration.c +++ b/hw/vfio/migration.c @@ -731,14 +731,6 @@ static int vfio_migration_query_flags(VFIODevice *vbasedev, uint64_t *mig_flags) feature->argsz = sizeof(buf); feature->flags = VFIO_DEVICE_FEATURE_GET | VFIO_DEVICE_FEATURE_MIGRATION; if (ioctl(vbasedev->fd, VFIO_DEVICE_FEATURE, feature)) { - if (errno == ENOTTY) { - error_report("%s: VFIO migration is not supported in kernel", - vbasedev->name); - } else { - error_report("%s: Failed to query VFIO migration support, err: %s", - vbasedev->name, strerror(errno)); - } - return -errno; } @@ -831,14 +823,28 @@ void vfio_reset_bytes_transferred(void) int vfio_migration_realize(VFIODevice *vbasedev, Error **errp) { - int ret = -ENOTSUP; + int ret; - if (!vbasedev->enable_migration) { + if (vbasedev->enable_migration == ON_OFF_AUTO_OFF) { + error_setg(&vbasedev->migration_blocker, + "%s: Migration is disabled for VFIO device", vbasedev->name); goto add_blocker; } ret = vfio_migration_init(vbasedev); if (ret) { + error_setg(&vbasedev->migration_blocker, + "%s: Migration couldn't be initialized for VFIO device, " + "err: %d (%s)", + vbasedev->name, ret, strerror(-ret)); + goto add_blocker; + } + + if (vbasedev->enable_migration == ON_OFF_AUTO_AUTO && + !vbasedev->dirty_pages_supported) { + error_setg(&vbasedev->migration_blocker, + "%s: VFIO device doesn't support device dirty tracking", + vbasedev->name); goto add_blocker; } @@ -856,9 +862,6 @@ int vfio_migration_realize(VFIODevice *vbasedev, Error **errp) return 0; add_blocker: - error_setg(&vbasedev->migration_blocker, - "VFIO device doesn't support migration"); - ret = migrate_add_blocker(vbasedev->migration_blocker, errp); if (ret < 0) { error_free(vbasedev->migration_blocker); diff --git a/hw/vfio/pci.c b/hw/vfio/pci.c index 73874a94de..48584e3b01 100644 --- a/hw/vfio/pci.c +++ b/hw/vfio/pci.c @@ -3347,8 +3347,8 @@ static Property vfio_pci_dev_properties[] = { VFIO_FEATURE_ENABLE_REQ_BIT, true), DEFINE_PROP_BIT("x-igd-opregion", VFIOPCIDevice, features, VFIO_FEATURE_ENABLE_IGD_OPREGION_BIT, false), - DEFINE_PROP_BOOL("x-enable-migration", VFIOPCIDevice, - vbasedev.enable_migration, false), + DEFINE_PROP_ON_OFF_AUTO("enable-migration", VFIOPCIDevice, + vbasedev.enable_migration, ON_OFF_AUTO_AUTO), DEFINE_PROP_BOOL("x-no-mmap", VFIOPCIDevice, vbasedev.no_mmap, false), DEFINE_PROP_BOOL("x-balloon-allowed", VFIOPCIDevice, vbasedev.ram_block_discard_allowed, false),
The major parts of VFIO migration are supported today in QEMU. This includes basic VFIO migration, device dirty page tracking and precopy support. Thus, at this point in time, it seems appropriate to make VFIO migration non-experimental: remove the x prefix from enable_migration property, change it to ON_OFF_AUTO and let the default value be AUTO. In addition, make the following adjustments: 1. Require device dirty tracking support when enable_migration is AUTO (i.e., not explicitly enabled). This is because device dirty tracking is currently the only method to do dirty page tracking, which is essential for migrating in a reasonable downtime. Setting enable_migration to ON will not require device dirty tracking. 2. Make migration blocker messages more elaborate. 3. Remove error prints in vfio_migration_query_flags(). 4. Remove a redundant assignment in vfio_migration_realize(). Signed-off-by: Avihai Horon <avihaih@nvidia.com> --- include/hw/vfio/vfio-common.h | 2 +- hw/vfio/migration.c | 29 ++++++++++++++++------------- hw/vfio/pci.c | 4 ++-- 3 files changed, 19 insertions(+), 16 deletions(-)