| Message ID | 20210603114835.847451-4-vkuznets@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | i386: KVM: expand Hyper-V features early | expand |
On Thu, Jun 03, 2021 at 01:48:29PM +0200, Vitaly Kuznetsov wrote: > Currently, the only eVMCS version, supported by KVM (and described in TLFS) > is '1'. When Enlightened VMCS feature is enabled, QEMU takes the supported > eVMCS version range (from KVM_CAP_HYPERV_ENLIGHTENED_VMCS enablement) and > puts it to guest visible CPUIDs. When (and if) eVMCS ver.2 appears a > problem on migration is expected: it doesn't seem to be possible to migrate > from a host supporting eVMCS ver.2 to a host, which only support eVMCS > ver.1. Isn't it possible and safe to expose eVMCS ver.1 to the guest on a host that supports ver.2? > > Hardcode eVMCS ver.1 as the result of 'hv-evmcs' enablement for now. Newer > eVMCS versions will have to have their own enablement options (e.g. > 'hv-evmcs=2'). > > Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com> > --- > docs/hyperv.txt | 2 +- > target/i386/kvm/kvm.c | 16 +++++++++++----- > 2 files changed, 12 insertions(+), 6 deletions(-) > > diff --git a/docs/hyperv.txt b/docs/hyperv.txt > index a51953daa833..000638a2fd38 100644 > --- a/docs/hyperv.txt > +++ b/docs/hyperv.txt > @@ -170,7 +170,7 @@ Recommended: hv-frequencies > 3.16. hv-evmcs > =============== > The enlightenment is nested specific, it targets Hyper-V on KVM guests. When > -enabled, it provides Enlightened VMCS feature to the guest. The feature > +enabled, it provides Enlightened VMCS version 1 feature to the guest. The feature > implements paravirtualized protocol between L0 (KVM) and L1 (Hyper-V) > hypervisors making L2 exits to the hypervisor faster. The feature is Intel-only. > Note: some virtualization features (e.g. Posted Interrupts) are disabled when > diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c > index c676ee8b38a7..d57eede5dc81 100644 > --- a/target/i386/kvm/kvm.c > +++ b/target/i386/kvm/kvm.c > @@ -1490,13 +1490,19 @@ static int hyperv_init_vcpu(X86CPU *cpu) > ret = kvm_vcpu_enable_cap(cs, KVM_CAP_HYPERV_ENLIGHTENED_VMCS, 0, > (uintptr_t)&evmcs_version); > > - if (ret < 0) { > - fprintf(stderr, "Hyper-V %s is not supported by kernel\n", > - kvm_hyperv_properties[HYPERV_FEAT_EVMCS].desc); > + /* > + * KVM is required to support EVMCS ver.1. as that's what 'hv-evmcs' > + * option sets. Note: we hardcode the maximum supported eVMCS version > + * to '1' as well so 'hv-evmcs' feature is migratable even when (and if) > + * ver.2 is implemented. A new option (e.g. 'hv-evmcs=2') will then have > + * to be added. > + */ > + if (ret < 0 || (uint8_t)evmcs_version > 1) { Wait, do you really want to get a fatal error every time, after a kernel upgrade? I was expecting this: vcpu_evmcs_version = 1; /* hardcoded, but can become configurable later */ ... kvm_vcpu_enable_cap(cs, KVM_CAP_HYPERV_ENLIGHTENED_VMCS, 0, (uintptr_t)&supported_evmcs_version); if (ret < 0 || supported_evmcs_version < vcpu_evmcs_version) { error_setg(...); return; } cpu->hyperv_nested[0] = vcpu_evmcs_version; > + error_report("Hyper-V %s verson 1 is not supported by kernel", > + kvm_hyperv_properties[HYPERV_FEAT_EVMCS].desc); > return ret; > } > - > - cpu->hyperv_nested[0] = evmcs_version; > + cpu->hyperv_nested[0] = (1 << 8) | 1; > } > > return 0; > -- > 2.31.1 >
Eduardo Habkost <ehabkost@redhat.com> writes: > On Thu, Jun 03, 2021 at 01:48:29PM +0200, Vitaly Kuznetsov wrote: >> Currently, the only eVMCS version, supported by KVM (and described in TLFS) >> is '1'. When Enlightened VMCS feature is enabled, QEMU takes the supported >> eVMCS version range (from KVM_CAP_HYPERV_ENLIGHTENED_VMCS enablement) and >> puts it to guest visible CPUIDs. When (and if) eVMCS ver.2 appears a >> problem on migration is expected: it doesn't seem to be possible to migrate >> from a host supporting eVMCS ver.2 to a host, which only support eVMCS >> ver.1. > > Isn't it possible and safe to expose eVMCS ver.1 to the guest on > a host that supports ver.2? We expose the supported range, guest is free to use any eVMCS version in the range (see below): > >> >> Hardcode eVMCS ver.1 as the result of 'hv-evmcs' enablement for now. Newer >> eVMCS versions will have to have their own enablement options (e.g. >> 'hv-evmcs=2'). >> >> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com> >> --- >> docs/hyperv.txt | 2 +- >> target/i386/kvm/kvm.c | 16 +++++++++++----- >> 2 files changed, 12 insertions(+), 6 deletions(-) >> >> diff --git a/docs/hyperv.txt b/docs/hyperv.txt >> index a51953daa833..000638a2fd38 100644 >> --- a/docs/hyperv.txt >> +++ b/docs/hyperv.txt >> @@ -170,7 +170,7 @@ Recommended: hv-frequencies >> 3.16. hv-evmcs >> =============== >> The enlightenment is nested specific, it targets Hyper-V on KVM guests. When >> -enabled, it provides Enlightened VMCS feature to the guest. The feature >> +enabled, it provides Enlightened VMCS version 1 feature to the guest. The feature >> implements paravirtualized protocol between L0 (KVM) and L1 (Hyper-V) >> hypervisors making L2 exits to the hypervisor faster. The feature is Intel-only. >> Note: some virtualization features (e.g. Posted Interrupts) are disabled when >> diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c >> index c676ee8b38a7..d57eede5dc81 100644 >> --- a/target/i386/kvm/kvm.c >> +++ b/target/i386/kvm/kvm.c >> @@ -1490,13 +1490,19 @@ static int hyperv_init_vcpu(X86CPU *cpu) >> ret = kvm_vcpu_enable_cap(cs, KVM_CAP_HYPERV_ENLIGHTENED_VMCS, 0, >> (uintptr_t)&evmcs_version); >> >> - if (ret < 0) { >> - fprintf(stderr, "Hyper-V %s is not supported by kernel\n", >> - kvm_hyperv_properties[HYPERV_FEAT_EVMCS].desc); >> + /* >> + * KVM is required to support EVMCS ver.1. as that's what 'hv-evmcs' >> + * option sets. Note: we hardcode the maximum supported eVMCS version >> + * to '1' as well so 'hv-evmcs' feature is migratable even when (and if) >> + * ver.2 is implemented. A new option (e.g. 'hv-evmcs=2') will then have >> + * to be added. >> + */ >> + if (ret < 0 || (uint8_t)evmcs_version > 1) { > > Wait, do you really want to get a fatal error every time, after a > kernel upgrade? > Here, evmcs_version (returned by kvm_vcpu_enable_cap()) represents a *range* of supported eVMCS versions: (evmcs_highest_supported_version << 8) | evmcs_lowest_supported_version Currently, this is 0x101 [1..1] range. The '(uint8_t)evmcs_version > 1' check here means 'eVMCS v1' is no longer supported by KVM. This is not going to happen any time soon, but I can imagine in 10 years or so we'll be dropping v1 so the range (in theory) can be [10..2] -- which would mean eVMCS ver. 1 is NOT supported. And we can't proceed then. > I was expecting this: > > vcpu_evmcs_version = 1; /* hardcoded, but can become configurable later */ > ... > kvm_vcpu_enable_cap(cs, KVM_CAP_HYPERV_ENLIGHTENED_VMCS, 0, (uintptr_t)&supported_evmcs_version); > if (ret < 0 || supported_evmcs_version < vcpu_evmcs_version) { > error_setg(...); > return; > } > cpu->hyperv_nested[0] = vcpu_evmcs_version; > > >> + error_report("Hyper-V %s verson 1 is not supported by kernel", >> + kvm_hyperv_properties[HYPERV_FEAT_EVMCS].desc); >> return ret; >> } >> - >> - cpu->hyperv_nested[0] = evmcs_version; >> + cpu->hyperv_nested[0] = (1 << 8) | 1; >> } >> >> return 0; >> -- >> 2.31.1 >>
On Fri, Jun 04, 2021 at 09:28:15AM +0200, Vitaly Kuznetsov wrote: > Eduardo Habkost <ehabkost@redhat.com> writes: > > > On Thu, Jun 03, 2021 at 01:48:29PM +0200, Vitaly Kuznetsov wrote: > >> Currently, the only eVMCS version, supported by KVM (and described in TLFS) > >> is '1'. When Enlightened VMCS feature is enabled, QEMU takes the supported > >> eVMCS version range (from KVM_CAP_HYPERV_ENLIGHTENED_VMCS enablement) and > >> puts it to guest visible CPUIDs. When (and if) eVMCS ver.2 appears a > >> problem on migration is expected: it doesn't seem to be possible to migrate > >> from a host supporting eVMCS ver.2 to a host, which only support eVMCS > >> ver.1. > > > > Isn't it possible and safe to expose eVMCS ver.1 to the guest on > > a host that supports ver.2? > > We expose the supported range, guest is free to use any eVMCS version in > the range (see below): Oh, I didn't notice the returned value was a range. > > > > >> > >> Hardcode eVMCS ver.1 as the result of 'hv-evmcs' enablement for now. Newer > >> eVMCS versions will have to have their own enablement options (e.g. > >> 'hv-evmcs=2'). > >> > >> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com> > >> --- > >> docs/hyperv.txt | 2 +- > >> target/i386/kvm/kvm.c | 16 +++++++++++----- > >> 2 files changed, 12 insertions(+), 6 deletions(-) > >> > >> diff --git a/docs/hyperv.txt b/docs/hyperv.txt > >> index a51953daa833..000638a2fd38 100644 > >> --- a/docs/hyperv.txt > >> +++ b/docs/hyperv.txt > >> @@ -170,7 +170,7 @@ Recommended: hv-frequencies > >> 3.16. hv-evmcs > >> =============== > >> The enlightenment is nested specific, it targets Hyper-V on KVM guests. When > >> -enabled, it provides Enlightened VMCS feature to the guest. The feature > >> +enabled, it provides Enlightened VMCS version 1 feature to the guest. The feature > >> implements paravirtualized protocol between L0 (KVM) and L1 (Hyper-V) > >> hypervisors making L2 exits to the hypervisor faster. The feature is Intel-only. > >> Note: some virtualization features (e.g. Posted Interrupts) are disabled when > >> diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c > >> index c676ee8b38a7..d57eede5dc81 100644 > >> --- a/target/i386/kvm/kvm.c > >> +++ b/target/i386/kvm/kvm.c > >> @@ -1490,13 +1490,19 @@ static int hyperv_init_vcpu(X86CPU *cpu) > >> ret = kvm_vcpu_enable_cap(cs, KVM_CAP_HYPERV_ENLIGHTENED_VMCS, 0, > >> (uintptr_t)&evmcs_version); > >> > >> - if (ret < 0) { > >> - fprintf(stderr, "Hyper-V %s is not supported by kernel\n", > >> - kvm_hyperv_properties[HYPERV_FEAT_EVMCS].desc); > >> + /* > >> + * KVM is required to support EVMCS ver.1. as that's what 'hv-evmcs' > >> + * option sets. Note: we hardcode the maximum supported eVMCS version > >> + * to '1' as well so 'hv-evmcs' feature is migratable even when (and if) > >> + * ver.2 is implemented. A new option (e.g. 'hv-evmcs=2') will then have > >> + * to be added. > >> + */ > >> + if (ret < 0 || (uint8_t)evmcs_version > 1) { > > > > Wait, do you really want to get a fatal error every time, after a > > kernel upgrade? > > > > Here, evmcs_version (returned by kvm_vcpu_enable_cap()) represents a > *range* of supported eVMCS versions: > > (evmcs_highest_supported_version << 8) | evmcs_lowest_supported_version > > Currently, this is 0x101 [1..1] range. > > The '(uint8_t)evmcs_version > 1' check here means 'eVMCS v1' is no > longer supported by KVM. This is not going to happen any time soon, but > I can imagine in 10 years or so we'll be dropping v1 so the range (in > theory) can be [10..2] -- which would mean eVMCS ver. 1 is NOT > supported. And we can't proceed then. Where is this documented? The only reference to KVM_CAP_HYPERV_ENLIGHTENED_VMCS I've found in linux/Documentation is this single sentence: | - HYPERV_CPUID_NESTED_FEATURES leaf and HV_X64_ENLIGHTENED_VMCS_RECOMMENDED | feature bit are only exposed when Enlightened VMCS was previously enabled | on the corresponding vCPU (KVM_CAP_HYPERV_ENLIGHTENED_VMCS). > >> ret = kvm_vcpu_enable_cap(cs, KVM_CAP_HYPERV_ENLIGHTENED_VMCS, 0, > >> (uintptr_t)&evmcs_version); > >> > >> - if (ret < 0) { > >> - fprintf(stderr, "Hyper-V %s is not supported by kernel\n", > >> - kvm_hyperv_properties[HYPERV_FEAT_EVMCS].desc); > >> + /* > >> + * KVM is required to support EVMCS ver.1. as that's what 'hv-evmcs' > >> + * option sets. Note: we hardcode the maximum supported eVMCS version > >> + * to '1' as well so 'hv-evmcs' feature is migratable even when (and if) > >> + * ver.2 is implemented. A new option (e.g. 'hv-evmcs=2') will then have > >> + * to be added. > >> + */ > >> + if (ret < 0 || (uint8_t)evmcs_version > 1) { Can we start with something that won't need to be rewritten after we change the guest evmcs version range? e.g.: static bool evmcs_version_supported(uint16_t version, uint32_t supported) { uint8_t min_ver = version; uint8_t max_ver = version >> 8; uint8_t min_supported = supported; uint8_t max_supported = supported >> 8; return (min_ver >= min_supported) && (max_ver <= max_supported); } ... #define DEFAULT_EVMCS_VERSION ((1 << 8) | 1) ... uint16_t evmcs_version = DEFAULT_EVMCS_VERSION; int ret = kvm_vcpu_enable_cap(cs, KVM_CAP_HYPERV_ENLIGHTENED_VMCS, 0, (uintptr_t)&supported_evmcs_version); if (ret < 0) { fprintf(...) return ret; } if (!evmcs_version_supported(evmcs_version, supported_evmcs_version)) { fprintf(...) return -ENOTSUP; } cpu->hyperv_nested[0] = evmcs_version; > > > I was expecting this: > > > > vcpu_evmcs_version = 1; /* hardcoded, but can become configurable later */ > > ... > > kvm_vcpu_enable_cap(cs, KVM_CAP_HYPERV_ENLIGHTENED_VMCS, 0, (uintptr_t)&supported_evmcs_version); > > if (ret < 0 || supported_evmcs_version < vcpu_evmcs_version) { > > error_setg(...); > > return; > > } > > cpu->hyperv_nested[0] = vcpu_evmcs_version; > > > > > >> + error_report("Hyper-V %s verson 1 is not supported by kernel", > >> + kvm_hyperv_properties[HYPERV_FEAT_EVMCS].desc); s/verson/version/ > >> return ret; What if ret is 0? > >> } > >> - > >> - cpu->hyperv_nested[0] = evmcs_version; > >> + cpu->hyperv_nested[0] = (1 << 8) | 1; > >> } > >> > >> return 0; > >> -- > >> 2.31.1 > >> > > -- > Vitaly >
Eduardo Habkost <ehabkost@redhat.com> writes: > On Fri, Jun 04, 2021 at 09:28:15AM +0200, Vitaly Kuznetsov wrote: >> Eduardo Habkost <ehabkost@redhat.com> writes: >> >> > On Thu, Jun 03, 2021 at 01:48:29PM +0200, Vitaly Kuznetsov wrote: >> >> Currently, the only eVMCS version, supported by KVM (and described in TLFS) >> >> is '1'. When Enlightened VMCS feature is enabled, QEMU takes the supported >> >> eVMCS version range (from KVM_CAP_HYPERV_ENLIGHTENED_VMCS enablement) and >> >> puts it to guest visible CPUIDs. When (and if) eVMCS ver.2 appears a >> >> problem on migration is expected: it doesn't seem to be possible to migrate >> >> from a host supporting eVMCS ver.2 to a host, which only support eVMCS >> >> ver.1. >> > >> > Isn't it possible and safe to expose eVMCS ver.1 to the guest on >> > a host that supports ver.2? >> >> We expose the supported range, guest is free to use any eVMCS version in >> the range (see below): > > Oh, I didn't notice the returned value was a range. > >> >> > >> >> >> >> Hardcode eVMCS ver.1 as the result of 'hv-evmcs' enablement for now. Newer >> >> eVMCS versions will have to have their own enablement options (e.g. >> >> 'hv-evmcs=2'). >> >> >> >> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com> >> >> --- >> >> docs/hyperv.txt | 2 +- >> >> target/i386/kvm/kvm.c | 16 +++++++++++----- >> >> 2 files changed, 12 insertions(+), 6 deletions(-) >> >> >> >> diff --git a/docs/hyperv.txt b/docs/hyperv.txt >> >> index a51953daa833..000638a2fd38 100644 >> >> --- a/docs/hyperv.txt >> >> +++ b/docs/hyperv.txt >> >> @@ -170,7 +170,7 @@ Recommended: hv-frequencies >> >> 3.16. hv-evmcs >> >> =============== >> >> The enlightenment is nested specific, it targets Hyper-V on KVM guests. When >> >> -enabled, it provides Enlightened VMCS feature to the guest. The feature >> >> +enabled, it provides Enlightened VMCS version 1 feature to the guest. The feature >> >> implements paravirtualized protocol between L0 (KVM) and L1 (Hyper-V) >> >> hypervisors making L2 exits to the hypervisor faster. The feature is Intel-only. >> >> Note: some virtualization features (e.g. Posted Interrupts) are disabled when >> >> diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c >> >> index c676ee8b38a7..d57eede5dc81 100644 >> >> --- a/target/i386/kvm/kvm.c >> >> +++ b/target/i386/kvm/kvm.c >> >> @@ -1490,13 +1490,19 @@ static int hyperv_init_vcpu(X86CPU *cpu) >> >> ret = kvm_vcpu_enable_cap(cs, KVM_CAP_HYPERV_ENLIGHTENED_VMCS, 0, >> >> (uintptr_t)&evmcs_version); >> >> >> >> - if (ret < 0) { >> >> - fprintf(stderr, "Hyper-V %s is not supported by kernel\n", >> >> - kvm_hyperv_properties[HYPERV_FEAT_EVMCS].desc); >> >> + /* >> >> + * KVM is required to support EVMCS ver.1. as that's what 'hv-evmcs' >> >> + * option sets. Note: we hardcode the maximum supported eVMCS version >> >> + * to '1' as well so 'hv-evmcs' feature is migratable even when (and if) >> >> + * ver.2 is implemented. A new option (e.g. 'hv-evmcs=2') will then have >> >> + * to be added. >> >> + */ >> >> + if (ret < 0 || (uint8_t)evmcs_version > 1) { >> > >> > Wait, do you really want to get a fatal error every time, after a >> > kernel upgrade? >> > >> >> Here, evmcs_version (returned by kvm_vcpu_enable_cap()) represents a >> *range* of supported eVMCS versions: >> >> (evmcs_highest_supported_version << 8) | evmcs_lowest_supported_version >> >> Currently, this is 0x101 [1..1] range. >> >> The '(uint8_t)evmcs_version > 1' check here means 'eVMCS v1' is no >> longer supported by KVM. This is not going to happen any time soon, but >> I can imagine in 10 years or so we'll be dropping v1 so the range (in >> theory) can be [10..2] -- which would mean eVMCS ver. 1 is NOT >> supported. And we can't proceed then. > > Where is this documented? The only reference to > KVM_CAP_HYPERV_ENLIGHTENED_VMCS I've found in linux/Documentation is this > single sentence: > > | - HYPERV_CPUID_NESTED_FEATURES leaf and HV_X64_ENLIGHTENED_VMCS_RECOMMENDED > | feature bit are only exposed when Enlightened VMCS was previously enabled > | on the corresponding vCPU (KVM_CAP_HYPERV_ENLIGHTENED_VMCS). > It seems that KVM_CAP_HYPERV_ENLIGHTENED_VMCS's documentation is indeed missing in KVM. > >> >> ret = kvm_vcpu_enable_cap(cs, KVM_CAP_HYPERV_ENLIGHTENED_VMCS, 0, >> >> (uintptr_t)&evmcs_version); >> >> >> >> - if (ret < 0) { >> >> - fprintf(stderr, "Hyper-V %s is not supported by kernel\n", >> >> - kvm_hyperv_properties[HYPERV_FEAT_EVMCS].desc); >> >> + /* >> >> + * KVM is required to support EVMCS ver.1. as that's what 'hv-evmcs' >> >> + * option sets. Note: we hardcode the maximum supported eVMCS version >> >> + * to '1' as well so 'hv-evmcs' feature is migratable even when (and if) >> >> + * ver.2 is implemented. A new option (e.g. 'hv-evmcs=2') will then have >> >> + * to be added. >> >> + */ >> >> + if (ret < 0 || (uint8_t)evmcs_version > 1) { > > Can we start with something that won't need to be rewritten after we change the > guest evmcs version range? e.g.: > > static bool evmcs_version_supported(uint16_t version, uint32_t supported) > { > uint8_t min_ver = version; > uint8_t max_ver = version >> 8; > uint8_t min_supported = supported; > uint8_t max_supported = supported >> 8; > return (min_ver >= min_supported) && (max_ver <= max_supported); > } > ... > #define DEFAULT_EVMCS_VERSION ((1 << 8) | 1) > ... > uint16_t evmcs_version = DEFAULT_EVMCS_VERSION; > int ret = kvm_vcpu_enable_cap(cs, KVM_CAP_HYPERV_ENLIGHTENED_VMCS, 0, > (uintptr_t)&supported_evmcs_version); > if (ret < 0) { > fprintf(...) > return ret; > } > if (!evmcs_version_supported(evmcs_version, supported_evmcs_version)) { > fprintf(...) > return -ENOTSUP; > } > cpu->hyperv_nested[0] = evmcs_version; > Sure, I don't have anything against an attempt to make this future proof. Will use this in v8, thanks!
diff --git a/docs/hyperv.txt b/docs/hyperv.txt index a51953daa833..000638a2fd38 100644 --- a/docs/hyperv.txt +++ b/docs/hyperv.txt @@ -170,7 +170,7 @@ Recommended: hv-frequencies 3.16. hv-evmcs =============== The enlightenment is nested specific, it targets Hyper-V on KVM guests. When -enabled, it provides Enlightened VMCS feature to the guest. The feature +enabled, it provides Enlightened VMCS version 1 feature to the guest. The feature implements paravirtualized protocol between L0 (KVM) and L1 (Hyper-V) hypervisors making L2 exits to the hypervisor faster. The feature is Intel-only. Note: some virtualization features (e.g. Posted Interrupts) are disabled when diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c index c676ee8b38a7..d57eede5dc81 100644 --- a/target/i386/kvm/kvm.c +++ b/target/i386/kvm/kvm.c @@ -1490,13 +1490,19 @@ static int hyperv_init_vcpu(X86CPU *cpu) ret = kvm_vcpu_enable_cap(cs, KVM_CAP_HYPERV_ENLIGHTENED_VMCS, 0, (uintptr_t)&evmcs_version); - if (ret < 0) { - fprintf(stderr, "Hyper-V %s is not supported by kernel\n", - kvm_hyperv_properties[HYPERV_FEAT_EVMCS].desc); + /* + * KVM is required to support EVMCS ver.1. as that's what 'hv-evmcs' + * option sets. Note: we hardcode the maximum supported eVMCS version + * to '1' as well so 'hv-evmcs' feature is migratable even when (and if) + * ver.2 is implemented. A new option (e.g. 'hv-evmcs=2') will then have + * to be added. + */ + if (ret < 0 || (uint8_t)evmcs_version > 1) { + error_report("Hyper-V %s verson 1 is not supported by kernel", + kvm_hyperv_properties[HYPERV_FEAT_EVMCS].desc); return ret; } - - cpu->hyperv_nested[0] = evmcs_version; + cpu->hyperv_nested[0] = (1 << 8) | 1; } return 0;
Currently, the only eVMCS version, supported by KVM (and described in TLFS) is '1'. When Enlightened VMCS feature is enabled, QEMU takes the supported eVMCS version range (from KVM_CAP_HYPERV_ENLIGHTENED_VMCS enablement) and puts it to guest visible CPUIDs. When (and if) eVMCS ver.2 appears a problem on migration is expected: it doesn't seem to be possible to migrate from a host supporting eVMCS ver.2 to a host, which only support eVMCS ver.1. Hardcode eVMCS ver.1 as the result of 'hv-evmcs' enablement for now. Newer eVMCS versions will have to have their own enablement options (e.g. 'hv-evmcs=2'). Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com> --- docs/hyperv.txt | 2 +- target/i386/kvm/kvm.c | 16 +++++++++++----- 2 files changed, 12 insertions(+), 6 deletions(-)