arch/x86/include/asm/svm.h | 1 + arch/x86/kvm/svm/avic.c | 55 +++++++++++++++++++++++++++----------- arch/x86/kvm/svm/nested.c | 3 +++ arch/x86/kvm/svm/svm.c | 3 +-- drivers/iommu/amd/iommu.c | 9 +++++++ 5 files changed, 54 insertions(+), 17 deletions(-)
Hi! This patch series includes several fixes to AVIC I found while working on a new version of nested AVIC code. Also while developing it I realized that a very simple workaround for AVIC's errata #1235 exists and included it in this patch series as well. Best regards, Maxim Levitsky Maxim Levitsky (5): x86: KVM: SVM: fix for x2avic CVE-2023-5090 x86: KVM: SVM: add support for Invalid IPI Vector interception x86: KVM: SVM: refresh AVIC inhibition in svm_leave_nested() iommu/amd: skip updating the IRTE entry when is_run is already false x86: KVM: SVM: workaround for AVIC's errata #1235 arch/x86/include/asm/svm.h | 1 + arch/x86/kvm/svm/avic.c | 55 +++++++++++++++++++++++++++----------- arch/x86/kvm/svm/nested.c | 3 +++ arch/x86/kvm/svm/svm.c | 3 +-- drivers/iommu/amd/iommu.c | 9 +++++++ 5 files changed, 54 insertions(+), 17 deletions(-) -- 2.26.3
On Thu, Sep 28, 2023 at 8:05 AM Maxim Levitsky <mlevitsk@redhat.com> wrote: > > Hi! > > This patch series includes several fixes to AVIC I found while working > on a new version of nested AVIC code. > > Also while developing it I realized that a very simple workaround for > AVIC's errata #1235 exists and included it in this patch series as well. > > Best regards, > Maxim Levitsky Can someone explain why we're still unwilling to enable AVIC by default? Have the performance issues that plagued the Rome implementation been fixed? What is AMD's guidance?
On Mon, 2024-03-25 at 20:15 -0700, Jim Mattson wrote: > > On Thu, Sep 28, 2023 at 8:05 AM Maxim Levitsky <mlevitsk@redhat.com> wrote: > > > > > > > > Hi! > > > > > > > > This patch series includes several fixes to AVIC I found while working > > > > on a new version of nested AVIC code. > > > > > > > > Also while developing it I realized that a very simple workaround for > > > > AVIC's errata #1235 exists and included it in this patch series as well. > > > > > > > > Best regards, > > > > Maxim Levitsky > > > > Can someone explain why we're still unwilling to enable AVIC by > > default? Have the performance issues that plagued the Rome > > implementation been fixed? What is AMD's guidance? > > Hi This is what I know: Zen1: I never tested it, so I don't know how well AVIC works there and if it has any erratas. Zen2: Has CPU errata in regard to IPI virtualization that makes it unusable in production, but if AVIC's IPI virtualization (borrowing the Intel term here) is disabled, then it works just fine and 1:1 equivalent to APICv without IPI. I posted patches for this several times, latest version is here, it still applies I think: https://lkml.iu.edu/hypermail/linux/kernel/2310.0/00790.html Zen3: For some reason AVIC got disabled by AMD in CPUID. It is still there though and force_avic=1 kvm_amd option can make KVM use it and AFAIK it works just fine. It is possible that it got disabled due to Zen2 errata that is fixed on Zen3, but maybe AMD wasn't sure back then that it will be fixed or it might be due to performance issues with broadcast IPIs which I think ended up being a software issue and was fixed a long time ago. Zen4+ I haven't tested it much, but AFAIK it should work out of the box. It also got x2avic mode which allows to use AVIC with VMs that have more that 254 vCPUs. IMHO if we merge the workaround I have for IPI virtualization and make IPI virtualization off for Zen2 (and maybe Zen1 as well), then I don't see why we can't make AVIC be the default on. Best regards, Maxim Levitsky
On 26/03/2024 15:59, mlevitsk@redhat.com wrote: > On Mon, 2024-03-25 at 20:15 -0700, Jim Mattson wrote: >>> On Thu, Sep 28, 2023 at 8:05 AM Maxim Levitsky <mlevitsk@redhat.com> wrote: >>>>> >>>>> Hi! >>>>> >>>>> This patch series includes several fixes to AVIC I found while working >>>>> on a new version of nested AVIC code. >>>>> >>>>> Also while developing it I realized that a very simple workaround for >>>>> AVIC's errata #1235 exists and included it in this patch series as well. >>>>> >>>>> Best regards, >>>>> Maxim Levitsky >>> >>> Can someone explain why we're still unwilling to enable AVIC by >>> default? Have the performance issues that plagued the Rome >>> implementation been fixed? What is AMD's guidance? >>> > Hi > > This is what I know: > > Zen1: > I never tested it, so I don't know how well AVIC works there and if it has any erratas. > > Zen2: > Has CPU errata in regard to IPI virtualization that makes it unusable in production, > but if AVIC's IPI virtualization (borrowing the Intel term here) is disabled, > then it works just fine and 1:1 equivalent to APICv without IPI. > > I posted patches for this several times, latest version is here, it still applies I think: > https://lkml.iu.edu/hypermail/linux/kernel/2310.0/00790.html > > Zen3: > For some reason AVIC got disabled by AMD in CPUID. It is still there though and force_avic=1 kvm_amd option > can make KVM use it and AFAIK it works just fine. > > It is possible that it got disabled due to Zen2 errata that is fixed on Zen3, > but maybe AMD wasn't sure back then that it will be fixed or it might be due to performance issues with broadcast > IPIs which I think ended up being a software issue and was fixed a long time ago. > > Zen4+ > I haven't tested it much, but AFAIK it should work out of the box. It also got x2avic mode which allows > to use AVIC with VMs that have more that 254 vCPUs. > > IMHO if we merge the workaround I have for IPI virtualization and make IPI virtualization off for Zen2 > (and maybe Zen1 as well), then I don't see why we can't make AVIC be the default on. Additionally, I think right now with avic=1 it fails vcpu creation when creating more a vcpu with an id bigger than what's supported i.e. the MAX_VCPUS we currently advertised in UAPI isn't quite honored. So that's the only wrinkle at least I am aware. Sean had send this one series to inhibit AVIC when such config: https://lore.kernel.org/linux-iommu/20230815213533.548732-1-seanjc@google.com/#r But I am not sure if it was respinned. Joao
© 2016 - 2025 Red Hat, Inc.