KVM: selftests: AVX support + fixes

[PATCH 00/11] KVM: selftests: AVX support + fixes

Posted by Sean Christopherson 1 year, 4 months ago

Enable CR4.OSXSAVE and XCR0.AVX by default when creating selftests vCPUs
in order to play nice with compilers that have been configured to enable
-march=x86-64-v3 by default.

While it would be easier to force v2 (or earlier), there are enough tests
that want XCR0 configured that it will (hopefully) be a net postive to
enable all XCR0 features by default.

The only real hiccup is the CR4/CPUID sync test, which disables CR4.OSXSAVE
to verify KVM toggles the associated CPUID bit.  And if it calls memset()
while OSXAVE is disabled, kablooie.  Fixing that requires a bit of assembly,
but overall I think it's worth carrying a few lines of assembly in order to
gain test coverage for running AVX instructions in guests, and boy are
compilers good at abusing AVX :-)

Fix a few bugs/warts found along the way.  Notably, the CPUID test has an
array out-of-bounds bug that can result in false passes (I only noticed
because it was getting a false pass on gcc).

Sean Christopherson (11):
  KVM: selftests: Fix out-of-bounds reads in CPUID test's array lookups
  KVM: selftests: Precisely mask off dynamic fields in CPUID test
  KVM: selftests: Mask off OSPKE and OSXSAVE when comparing CPUID
    entries
  KVM: selftests: Rework OSXSAVE CR4=>CPUID test to play nice with AVX
    insns
  KVM: selftests: Configure XCR0 to max supported value by default
  KVM: selftests: Verify XCR0 can be "downgraded" and "upgraded"
  KVM: selftests: Drop manual CR4.OSXSAVE enabling from CR4/CPUID sync
    test
  KVM: selftests: Drop manual XCR0 configuration from AMX test
  KVM: selftests: Drop manual XCR0 configuration from state test
  KVM: selftests: Drop manual XCR0 configuration from SEV smoke test
  KVM: selftests: Ensure KVM supports AVX for SEV-ES VMSA FPU test

 .../selftests/kvm/include/x86_64/processor.h  |  5 ++
 .../selftests/kvm/lib/x86_64/processor.c      | 24 +++++++
 tools/testing/selftests/kvm/x86_64/amx_test.c | 23 ++-----
 .../testing/selftests/kvm/x86_64/cpuid_test.c | 67 ++++++++++++-------
 .../kvm/x86_64/cr4_cpuid_sync_test.c          | 53 +++++++++------
 .../selftests/kvm/x86_64/sev_smoke_test.c     | 19 ++----
 .../testing/selftests/kvm/x86_64/state_test.c |  5 --
 .../selftests/kvm/x86_64/xcr0_cpuid_test.c    | 11 ++-
 8 files changed, 122 insertions(+), 85 deletions(-)


base-commit: efbc6bd090f48ccf64f7a8dd5daea775821d57ec
-- 
2.47.0.rc0.187.ge670bccf7e-goog

Re: [PATCH 00/11] KVM: selftests: AVX support + fixes

Posted by Sean Christopherson 1 year, 3 months ago

On Thu, 03 Oct 2024 16:43:26 -0700, Sean Christopherson wrote:
> Enable CR4.OSXSAVE and XCR0.AVX by default when creating selftests vCPUs
> in order to play nice with compilers that have been configured to enable
> -march=x86-64-v3 by default.
> 
> While it would be easier to force v2 (or earlier), there are enough tests
> that want XCR0 configured that it will (hopefully) be a net postive to
> enable all XCR0 features by default.
> 
> [...]

Applied to kvm-x86 selftests, minus patch 1 which went into 6.12.  At some point
in the 6.13 cycle I'll send a revert for the "march" madness.

[01/11] KVM: selftests: Fix out-of-bounds reads in CPUID test's array lookups
        (no commit info)
[02/11] KVM: selftests: Precisely mask off dynamic fields in CPUID test
        https://github.com/kvm-x86/linux/commit/c0124e2e74a7
[03/11] KVM: selftests: Mask off OSPKE and OSXSAVE when comparing CPUID entries
        https://github.com/kvm-x86/linux/commit/01e2827157ef
[04/11] KVM: selftests: Rework OSXSAVE CR4=>CPUID test to play nice with AVX insns
        https://github.com/kvm-x86/linux/commit/cf50f01336d3
[05/11] KVM: selftests: Configure XCR0 to max supported value by default
        https://github.com/kvm-x86/linux/commit/331b8ddaebc1
[06/11] KVM: selftests: Verify XCR0 can be "downgraded" and "upgraded"
        https://github.com/kvm-x86/linux/commit/d87b459428c0
[07/11] KVM: selftests: Drop manual CR4.OSXSAVE enabling from CR4/CPUID sync test
        https://github.com/kvm-x86/linux/commit/86502f01b8b9
[08/11] KVM: selftests: Drop manual XCR0 configuration from AMX test
        https://github.com/kvm-x86/linux/commit/fd7b6d77fa6d
[09/11] KVM: selftests: Drop manual XCR0 configuration from state test
        https://github.com/kvm-x86/linux/commit/818646fea3ea
[10/11] KVM: selftests: Drop manual XCR0 configuration from SEV smoke test
        https://github.com/kvm-x86/linux/commit/ce22d24024ea
[11/11] KVM: selftests: Ensure KVM supports AVX for SEV-ES VMSA FPU test
        https://github.com/kvm-x86/linux/commit/08cc7ab1a6ca

--
https://github.com/kvm-x86/linux/tree/next

Re: [PATCH 00/11] KVM: selftests: AVX support + fixes

Posted by Sean Christopherson 1 year, 3 months ago

On Thu, Oct 31, 2024, Sean Christopherson wrote:
> On Thu, 03 Oct 2024 16:43:26 -0700, Sean Christopherson wrote:
> > Enable CR4.OSXSAVE and XCR0.AVX by default when creating selftests vCPUs
> > in order to play nice with compilers that have been configured to enable
> > -march=x86-64-v3 by default.
> > 
> > While it would be easier to force v2 (or earlier), there are enough tests
> > that want XCR0 configured that it will (hopefully) be a net postive to
> > enable all XCR0 features by default.
> > 
> > [...]
> 
> Applied to kvm-x86 selftests, minus patch 1 which went into 6.12.  At some point
> in the 6.13 cycle I'll send a revert for the "march" madness.
> 
> [01/11] KVM: selftests: Fix out-of-bounds reads in CPUID test's array lookups
>         (no commit info)
> [02/11] KVM: selftests: Precisely mask off dynamic fields in CPUID test
>         https://github.com/kvm-x86/linux/commit/c0124e2e74a7
> [03/11] KVM: selftests: Mask off OSPKE and OSXSAVE when comparing CPUID entries
>         https://github.com/kvm-x86/linux/commit/01e2827157ef
> [04/11] KVM: selftests: Rework OSXSAVE CR4=>CPUID test to play nice with AVX insns
>         https://github.com/kvm-x86/linux/commit/cf50f01336d3
> [05/11] KVM: selftests: Configure XCR0 to max supported value by default
>         https://github.com/kvm-x86/linux/commit/331b8ddaebc1
> [06/11] KVM: selftests: Verify XCR0 can be "downgraded" and "upgraded"
>         https://github.com/kvm-x86/linux/commit/d87b459428c0
> [07/11] KVM: selftests: Drop manual CR4.OSXSAVE enabling from CR4/CPUID sync test
>         https://github.com/kvm-x86/linux/commit/86502f01b8b9
> [08/11] KVM: selftests: Drop manual XCR0 configuration from AMX test
>         https://github.com/kvm-x86/linux/commit/fd7b6d77fa6d
> [09/11] KVM: selftests: Drop manual XCR0 configuration from state test
>         https://github.com/kvm-x86/linux/commit/818646fea3ea
> [10/11] KVM: selftests: Drop manual XCR0 configuration from SEV smoke test
>         https://github.com/kvm-x86/linux/commit/ce22d24024ea
> [11/11] KVM: selftests: Ensure KVM supports AVX for SEV-ES VMSA FPU test
>         https://github.com/kvm-x86/linux/commit/08cc7ab1a6ca

And because I mucked up the mmu_stress_test/vcpu_get_reg() series and had to yank
it out, the hashes for this series got changed:

[02/11] KVM: selftests: Precisely mask off dynamic fields in CPUID test
        https://github.com/kvm-x86/linux/commit/f2c5aa31670d
[03/11] KVM: selftests: Mask off OSPKE and OSXSAVE when comparing CPUID entries
        https://github.com/kvm-x86/linux/commit/164cea33bfed
[04/11] KVM: selftests: Rework OSXSAVE CR4=>CPUID test to play nice with AVX insns
        https://github.com/kvm-x86/linux/commit/2b9a126a2986
[05/11] KVM: selftests: Configure XCR0 to max supported value by default
        https://github.com/kvm-x86/linux/commit/8b14c4d85d03
[06/11] KVM: selftests: Verify XCR0 can be "downgraded" and "upgraded"
        https://github.com/kvm-x86/linux/commit/8ae01bf64caa
[07/11] KVM: selftests: Drop manual CR4.OSXSAVE enabling from CR4/CPUID sync test
        https://github.com/kvm-x86/linux/commit/3678c7f6114f
[08/11] KVM: selftests: Drop manual XCR0 configuration from AMX test
        https://github.com/kvm-x86/linux/commit/d87331890a38
[09/11] KVM: selftests: Drop manual XCR0 configuration from state test
        https://github.com/kvm-x86/linux/commit/28439090ece6
[10/11] KVM: selftests: Drop manual XCR0 configuration from SEV smoke test
        https://github.com/kvm-x86/linux/commit/3c4c128d02ed
[11/11] KVM: selftests: Ensure KVM supports AVX for SEV-ES VMSA FPU test
        https://github.com/kvm-x86/linux/commit/89f8869835e4

Re: [PATCH 00/11] KVM: selftests: AVX support + fixes

Posted by Paolo Bonzini 1 year, 3 months ago

On 10/4/24 01:43, Sean Christopherson wrote:
> Enable CR4.OSXSAVE and XCR0.AVX by default when creating selftests vCPUs
> in order to play nice with compilers that have been configured to enable
> -march=x86-64-v3 by default.
> 
> While it would be easier to force v2 (or earlier), there are enough tests
> that want XCR0 configured that it will (hopefully) be a net postive to
> enable all XCR0 features by default.
> 
> The only real hiccup is the CR4/CPUID sync test, which disables CR4.OSXSAVE
> to verify KVM toggles the associated CPUID bit.  And if it calls memset()
> while OSXAVE is disabled, kablooie.  Fixing that requires a bit of assembly,
> but overall I think it's worth carrying a few lines of assembly in order to
> gain test coverage for running AVX instructions in guests, and boy are
> compilers good at abusing AVX :-)
> 
> Fix a few bugs/warts found along the way.  Notably, the CPUID test has an
> array out-of-bounds bug that can result in false passes (I only noticed
> because it was getting a false pass on gcc).

I think this is not -rc/stable material, so for now I'm applying 
Vitaly's patch, plus patch 1 from this series.

Paolo

> Sean Christopherson (11):
>    KVM: selftests: Fix out-of-bounds reads in CPUID test's array lookups
>    KVM: selftests: Precisely mask off dynamic fields in CPUID test
>    KVM: selftests: Mask off OSPKE and OSXSAVE when comparing CPUID
>      entries
>    KVM: selftests: Rework OSXSAVE CR4=>CPUID test to play nice with AVX
>      insns
>    KVM: selftests: Configure XCR0 to max supported value by default
>    KVM: selftests: Verify XCR0 can be "downgraded" and "upgraded"
>    KVM: selftests: Drop manual CR4.OSXSAVE enabling from CR4/CPUID sync
>      test
>    KVM: selftests: Drop manual XCR0 configuration from AMX test
>    KVM: selftests: Drop manual XCR0 configuration from state test
>    KVM: selftests: Drop manual XCR0 configuration from SEV smoke test
>    KVM: selftests: Ensure KVM supports AVX for SEV-ES VMSA FPU test
> 
>   .../selftests/kvm/include/x86_64/processor.h  |  5 ++
>   .../selftests/kvm/lib/x86_64/processor.c      | 24 +++++++
>   tools/testing/selftests/kvm/x86_64/amx_test.c | 23 ++-----
>   .../testing/selftests/kvm/x86_64/cpuid_test.c | 67 ++++++++++++-------
>   .../kvm/x86_64/cr4_cpuid_sync_test.c          | 53 +++++++++------
>   .../selftests/kvm/x86_64/sev_smoke_test.c     | 19 ++----
>   .../testing/selftests/kvm/x86_64/state_test.c |  5 --
>   .../selftests/kvm/x86_64/xcr0_cpuid_test.c    | 11 ++-
>   8 files changed, 122 insertions(+), 85 deletions(-)
> 
> 
> base-commit: efbc6bd090f48ccf64f7a8dd5daea775821d57ec