| Message ID | 20240723072004.1470688-1-shahuang@redhat.com (mailing list archive) |
|---|---|
| Headers | show |
| Series | Allow userspace to change ID_AA64PFR1_EL1 | expand |
Hi Marc, Oliver, Kindly ping for this series. Welcome your feedbacks. I wonder if this implementation satisfy your expectation? Thanks, Shaoqin On 7/23/24 15:19, Shaoqin Huang wrote: > Hi guys, > > This is another try to allow userspace to change ID_AA64PFR1_EL1, and we want to > give userspace the ability to control the visible feature set for a VM, which > could be used by userspace in such a way to transparently migrate VMs. > > The patch series have four part: > > The first patch disable those fields which KVM doesn't know how to handle, so > KVM will only expose value 0 of those fields to the guest. > > The second patch check the FEAT_SSBS in guest IDREG instead of the cpu > capability. > > The third patch allow userspace to change ID_AA64PFR1_EL1, it only advertise the > fields known to KVM and leave others unadvertise. > > The fourth patch adds the kselftest to test if userspace can change the > ID_AA64PFR1_EL1. > > Besides, I also noticed there is another patch [1] which try to make the > ID_AA64PFR1_EL1 writable. This patch [1] is try to enable GCS on baremental, and > add GCS support for the guest. What I understand is if we have GCS support on > baremental, it will be clear to how to handle them in KVM. And same for other > fields like NMI, THE, DF2, MTEX.. At that time, they can be writable. > > [1] [PATCH v9 13/39] KVM: arm64: Manage GCS registers for guests > https://lore.kernel.org/all/20240625-arm64-gcs-v9-13-0f634469b8f0@kernel.org/ > > Changelog: > ---------- > v4 -> v5: > * Only advertise fields which KVM know how to handle to userspace, leave > others unadvertised. > * Add a new patch to check FEAT_SSBS in IDREG instead of cpu capability. > * Tweak the kselftest writable fields. > * Improve the commit message. > > v3 -> v4: > * Add a new patch to disable some feature which KVM doesn't know how to > handle in the register accessor. > * Handle all the fields in the register. > * Fixes a small cnt issue in kselftest. > > v2 -> v3: > * Give more description about why only part of the fields can be writable. > * Updated the writable mask by referring the latest ARM spec. > > v1 -> v2: > * Tackling the full register instead of single field. > * Changing the patch title and commit message. > > RFCv1 -> v1: > * Fix the compilation error. > * Delete the machine specific information and make the description more > generable. > > RFCv1: https://lore.kernel.org/all/20240612023553.127813-1-shahuang@redhat.com/ > v1: https://lore.kernel.org/all/20240617075131.1006173-1-shahuang@redhat.com/ > v2: https://lore.kernel.org/all/20240618063808.1040085-1-shahuang@redhat.com/ > v3: https://lore.kernel.org/all/20240628060454.1936886-2-shahuang@redhat.com/ > v4: https://lore.kernel.org/all/20240718035017.434996-1-shahuang@redhat.com/ > > Shaoqin Huang (4): > KVM: arm64: Disable fields that KVM doesn't know how to handle in > ID_AA64PFR1_EL1 > KVM: arm64: Use kvm_has_feat() to check if FEAT_SSBS is advertised to > the guest > KVM: arm64: Allow userspace to change ID_AA64PFR1_EL1 > KVM: selftests: aarch64: Add writable test for ID_AA64PFR1_EL1 > > arch/arm64/kvm/hypercalls.c | 12 +++++----- > arch/arm64/kvm/sys_regs.c | 22 ++++++++++++++++++- > .../selftests/kvm/aarch64/set_id_regs.c | 14 +++++++++--- > 3 files changed, 38 insertions(+), 10 deletions(-) >
On Tue, 23 Jul 2024 08:19:59 +0100, Shaoqin Huang <shahuang@redhat.com> wrote: > > Hi guys, > > This is another try to allow userspace to change ID_AA64PFR1_EL1, and we want to > give userspace the ability to control the visible feature set for a VM, which > could be used by userspace in such a way to transparently migrate VMs. I think this looks OK now, thanks for going through the motions and doing the right thing. What is missing is similar handling for 32bit ID registers, but I'm not sure we keen on going down that road -- machines capable of running those are on their way out. This can be done later anyway, should anyone care. > > The patch series have four part: > > The first patch disable those fields which KVM doesn't know how to handle, so > KVM will only expose value 0 of those fields to the guest. > > The second patch check the FEAT_SSBS in guest IDREG instead of the cpu > capability. > > The third patch allow userspace to change ID_AA64PFR1_EL1, it only advertise the > fields known to KVM and leave others unadvertise. > > The fourth patch adds the kselftest to test if userspace can change the > ID_AA64PFR1_EL1. > > Besides, I also noticed there is another patch [1] which try to make the > ID_AA64PFR1_EL1 writable. This patch [1] is try to enable GCS on baremental, and > add GCS support for the guest. What I understand is if we have GCS support on > baremental, it will be clear to how to handle them in KVM. And same for other > fields like NMI, THE, DF2, MTEX.. At that time, they can be > writable. I expect that Broonie would look into this as part of his series. Thanks, M.
On Tue, 23 Jul 2024 03:19:59 -0400, Shaoqin Huang wrote: > This is another try to allow userspace to change ID_AA64PFR1_EL1, and we want to > give userspace the ability to control the visible feature set for a VM, which > could be used by userspace in such a way to transparently migrate VMs. > > The patch series have four part: > > The first patch disable those fields which KVM doesn't know how to handle, so > KVM will only expose value 0 of those fields to the guest. > > [...] Applied to next, thanks! [1/4] KVM: arm64: Disable fields that KVM doesn't know how to handle in ID_AA64PFR1_EL1 commit: ffe68b2d19a5a84440fea99a732cfc3b157559eb [2/4] KVM: arm64: Use kvm_has_feat() to check if FEAT_SSBS is advertised to the guest commit: e8d164974cfa46fe5ec87869c8a7113641f322d5 [3/4] KVM: arm64: Allow userspace to change ID_AA64PFR1_EL1 commit: 78c4446b5f957fb14737582e503b1b25f66edc45 [4/4] KVM: selftests: aarch64: Add writable test for ID_AA64PFR1_EL1 commit: dc9b5d7e0bd40e68a94013766b27be3dda10c006 Cheers, M.
On Sun, Aug 25, 2024 at 05:46:36PM +0100, Marc Zyngier wrote: > On Tue, 23 Jul 2024 08:19:59 +0100, > Shaoqin Huang <shahuang@redhat.com> wrote: > > > > Hi guys, > > > > This is another try to allow userspace to change ID_AA64PFR1_EL1, and we want to > > give userspace the ability to control the visible feature set for a VM, which > > could be used by userspace in such a way to transparently migrate VMs. > > > I think this looks OK now, thanks for going through the motions and > doing the right thing. > > What is missing is similar handling for 32bit ID registers, but I'm > not sure we keen on going down that road -- machines capable of > running those are on their way out. This can be done later anyway, > should anyone care. The Aarch32 ID registers need doing - we've already established that fact. Sadly, you decided you wouldn't respond to my patch addressing one of the Aarch32 ID registers despite me sending follow-ups to nicely ask you about this - you seemed to go utterly silent on it. The Aarch32 ID registers have changed value between different kernel versions, and given that QEMU saves and restores _all_ ID registers, changes to these ID registers cause a regression if one attempts to migrate VMs between one kernel version and the next. It doesn't even have to be between two physical machines. Libvirt supports managed- saving on reboot, where it saves an image of a VM at shutdown, and restores it at the next reboot. These changes in ID registers render effectively data loss in VMs that have been managed-saved - the saved state of the VM has to either be destroyed, or the host kernel reverted back and _never_ moved forward. As you don't seem to be keen to address this (by ignoring my emails on the topic, and now suggesting in your response above that you're not keen to do anything with the Aarch32 ID registers, I guess this just means that KVM on Aarch64 is going to forever suck. I'm sure Oliver will recall my emails on this which you've decided to ignore... he was supportive of my efforts to address this.
On Sun, 25 Aug 2024 18:09:48 +0100, "Russell King (Oracle)" <linux@armlinux.org.uk> wrote: > > On Sun, Aug 25, 2024 at 05:46:36PM +0100, Marc Zyngier wrote: > > On Tue, 23 Jul 2024 08:19:59 +0100, > > Shaoqin Huang <shahuang@redhat.com> wrote: > > > > > > Hi guys, > > > > > > This is another try to allow userspace to change ID_AA64PFR1_EL1, and we want to > > > give userspace the ability to control the visible feature set for a VM, which > > > could be used by userspace in such a way to transparently migrate VMs. > > > > > > I think this looks OK now, thanks for going through the motions and > > doing the right thing. > > > > What is missing is similar handling for 32bit ID registers, but I'm > > not sure we keen on going down that road -- machines capable of > > running those are on their way out. This can be done later anyway, > > should anyone care. > > The Aarch32 ID registers need doing - we've already established that > fact. Sadly, you decided you wouldn't respond to my patch addressing > one of the Aarch32 ID registers despite me sending follow-ups to nicely > ask you about this - you seemed to go utterly silent on it. No, Russell. *you* went utterly silent after your May patch. You sent an RFC, to which people responded. Given that your last email on the subject was almost 4 months ago and that you never brought the subject up again, it can't be that big a deal. To me, an RFC means "I have this idea, and I'm not sure how to do it". An RFC is usually only a proof of concept that has no purpose being taken at face value. If you want a patch taken seriously, don't send it as an RFC. And send it again if nobody replies. It's not that this is anything new. > The Aarch32 ID registers have changed value between different kernel > versions, and given that QEMU saves and restores _all_ ID registers, > changes to these ID registers cause a regression if one attempts to > migrate VMs between one kernel version and the next. It doesn't even > have to be between two physical machines. Libvirt supports managed- > saving on reboot, where it saves an image of a VM at shutdown, and > restores it at the next reboot. These changes in ID registers render > effectively data loss in VMs that have been managed-saved - the > saved state of the VM has to either be destroyed, or the host kernel > reverted back and _never_ moved forward. > > As you don't seem to be keen to address this (by ignoring my emails > on the topic, and now suggesting in your response above that you're > not keen to do anything with the Aarch32 ID registers, I guess this > just means that KVM on Aarch64 is going to forever suck. I'm fine with that. Nobody is forced to use it, and I don't feel the need to put extra effort on things I don't care about any more. AArch32 support is one of these things, amongst many others. If you want the support to improve, I suggest you send patches. And send them again if no reply shows up in a timely manner. Because you're probably the last person who gives a damn about the AArch32 support in KVM. And if not even you can be bothered to fix it, then support for AArch32 EL1 should probably be removed altogether (I'm all for deleting unused code). > I'm sure Oliver will recall my emails on this which you've decided to > ignore... he was supportive of my efforts to address this. I'm supportive as well. I'm just not going to fix it for you. M.
Hi guys, This is another try to allow userspace to change ID_AA64PFR1_EL1, and we want to give userspace the ability to control the visible feature set for a VM, which could be used by userspace in such a way to transparently migrate VMs. The patch series have four part: The first patch disable those fields which KVM doesn't know how to handle, so KVM will only expose value 0 of those fields to the guest. The second patch check the FEAT_SSBS in guest IDREG instead of the cpu capability. The third patch allow userspace to change ID_AA64PFR1_EL1, it only advertise the fields known to KVM and leave others unadvertise. The fourth patch adds the kselftest to test if userspace can change the ID_AA64PFR1_EL1. Besides, I also noticed there is another patch [1] which try to make the ID_AA64PFR1_EL1 writable. This patch [1] is try to enable GCS on baremental, and add GCS support for the guest. What I understand is if we have GCS support on baremental, it will be clear to how to handle them in KVM. And same for other fields like NMI, THE, DF2, MTEX.. At that time, they can be writable. [1] [PATCH v9 13/39] KVM: arm64: Manage GCS registers for guests https://lore.kernel.org/all/20240625-arm64-gcs-v9-13-0f634469b8f0@kernel.org/ Changelog: ---------- v4 -> v5: * Only advertise fields which KVM know how to handle to userspace, leave others unadvertised. * Add a new patch to check FEAT_SSBS in IDREG instead of cpu capability. * Tweak the kselftest writable fields. * Improve the commit message. v3 -> v4: * Add a new patch to disable some feature which KVM doesn't know how to handle in the register accessor. * Handle all the fields in the register. * Fixes a small cnt issue in kselftest. v2 -> v3: * Give more description about why only part of the fields can be writable. * Updated the writable mask by referring the latest ARM spec. v1 -> v2: * Tackling the full register instead of single field. * Changing the patch title and commit message. RFCv1 -> v1: * Fix the compilation error. * Delete the machine specific information and make the description more generable. RFCv1: https://lore.kernel.org/all/20240612023553.127813-1-shahuang@redhat.com/ v1: https://lore.kernel.org/all/20240617075131.1006173-1-shahuang@redhat.com/ v2: https://lore.kernel.org/all/20240618063808.1040085-1-shahuang@redhat.com/ v3: https://lore.kernel.org/all/20240628060454.1936886-2-shahuang@redhat.com/ v4: https://lore.kernel.org/all/20240718035017.434996-1-shahuang@redhat.com/ Shaoqin Huang (4): KVM: arm64: Disable fields that KVM doesn't know how to handle in ID_AA64PFR1_EL1 KVM: arm64: Use kvm_has_feat() to check if FEAT_SSBS is advertised to the guest KVM: arm64: Allow userspace to change ID_AA64PFR1_EL1 KVM: selftests: aarch64: Add writable test for ID_AA64PFR1_EL1 arch/arm64/kvm/hypercalls.c | 12 +++++----- arch/arm64/kvm/sys_regs.c | 22 ++++++++++++++++++- .../selftests/kvm/aarch64/set_id_regs.c | 14 +++++++++--- 3 files changed, 38 insertions(+), 10 deletions(-)