Re: [PATCH v8 20/20] KVM: x86: selftests: Add APX state handling and XCR0 sanity checks

[Jim Mattson]

On Wed, Sep 30, 2026 at 2:40 PM Chang S. Bae <chang.seok.bae@xxxxxxxxx> wrote:
>
> Now that KVM exposes the APX feature to guests, extend some existing
> selftests to validate XCR0 configuration and state management.
>
> Since APX repurposes the XSAVE area previously used by MPX in the
> non-compacted format, add a check to ensure that MPX state is not set
> when APX is enabled.
>
> Also, load non-init APX state data in the guest so that XSTATE_BV[APX] is
> set, allowing validation of APX state testing.
>
> Signed-off-by: Chang S. Bae <chang.seok.bae@xxxxxxxxx>
> ---
>  tools/testing/selftests/kvm/x86/state_test.c  |  3 +++
>  .../selftests/kvm/x86/xcr0_cpuid_test.c       | 19 +++++++++++++++++++
>  2 files changed, 22 insertions(+)
>
> diff --git a/tools/testing/selftests/kvm/x86/state_test.c b/tools/testing/selftests/kvm/x86/state_test.c
> index 4a1056a6cb8d..9727dbb2b981 100644
> --- a/tools/testing/selftests/kvm/x86/state_test.c
> +++ b/tools/testing/selftests/kvm/x86/state_test.c
> @@ -164,6 +164,9 @@ static void __attribute__((__flatten__)) guest_code(void *arg)
>                         asm volatile ("vmovupd %0, %%zmm16" :: "m" (buffer));
>                 }
>
> +               if (supported_xcr0 & XFEATURE_MASK_APX)
> +                       write_egpr(16, 0xcccccccc);
> +

Nit: to match MPX and PKU below:

        if (this_cpu_has(X86_FEATURE_APX)) {
            GUEST_ASSERT(supported_xcr0 & XFEATURE_MASK_APX);
            write_egpr(16, 0xcccccccc);
        }

[ ... ]

> +#define ASSERT_XFEATURE_CONFLICT(supported_xcr0, xfeatures, conflicts)                 \
> +do {                                                                                   \
> +       uint64_t __supported = (supported_xcr0) & ((xfeatures) | (conflicts));          \

Nit: u64

Reviewed-by: Jim Mattson <jmattson@xxxxxxxxxx>