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

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Message-ID: <206dbca3-1dbd-478c-9c3a-85d25f4f4ed6@redhat.com>
Date: Sun, 20 Oct 2024 13:28:58 +0200
From: Paolo Bonzini <pbonzini@...hat.com>
To: Sean Christopherson <seanjc@...gle.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
 Vitaly Kuznetsov <vkuznets@...hat.com>
Subject: Re: [PATCH 00/11] KVM: selftests: AVX support + fixes

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