Re: [PATCH 0/3] Clean up AMX cpuid bits XTILE_CFG and XTILE_DATA

From: Jim Mattson <jmattson@google.com>
To: Aaron Lewis <aaronlewis@google.com>
Cc: kvm@vger.kernel.org, pbonzini@redhat.com, seanjc@google.com,
	like.xu.linux@gmail.com
Subject: Re: [PATCH 0/3] Clean up AMX cpuid bits XTILE_CFG and XTILE_DATA
Date: Tue, 27 Dec 2022 12:00:49 -0800	[thread overview]
Message-ID: <CALMp9eRe+8ypPXVvR5cwRT7YeuXFtT2HjiyGOU9a1U5WjoD0Pw@mail.gmail.com> (raw)
In-Reply-To: <20221227183713.29140-1-aaronlewis@google.com>

On Tue, Dec 27, 2022 at 10:38 AM Aaron Lewis <aaronlewis@google.com> wrote:
>
> When running a SPR guest without AMX enabled

Can you clarify what "without AMX enabled" means? Do you mean that
userspace hasn't opted in to AMX via arch_prctl()?

> CPUID.(EAX=0DH,ECX=0):EAX.XTILE_CFG[bit-17] will be set and
> CPUID.(EAX=0DH,ECX=0):EAX.XTILE_DATA[bit-18] will be clear.  While this
> is architecturally correct it can be a little awkward for userspace
> or a guest when using them.  Instead of leaving the CPUID leaf in a
> half baked state, either clear them both or leave them both set.
>
> Additionally, add testing to verify the CPUID isn't in such a state.
>
> Aaron Lewis (3):
>   KVM: x86: Clear XTILE_CFG if XTILE_DATA is clear
>   KVM: selftests: Hoist XGETBV and XSETBV to make them more accessible
>   KVM: selftests: Add XCR0 Test
>
>  arch/x86/kvm/cpuid.c                          |   4 +
>  tools/testing/selftests/kvm/Makefile          |   1 +
>  .../selftests/kvm/include/x86_64/processor.h  |  19 +++
>  tools/testing/selftests/kvm/x86_64/amx_test.c |  24 +---
>  .../selftests/kvm/x86_64/xcr0_cpuid_test.c    | 134 ++++++++++++++++++
>  5 files changed, 161 insertions(+), 21 deletions(-)
>  create mode 100644 tools/testing/selftests/kvm/x86_64/xcr0_cpuid_test.c
>
> --
> 2.39.0.314.g84b9a713c41-goog
>