linux-kernel - Re: [PATCH v3 06/13] KVM: selftests: x86: Add the XFD check to IA32

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Message-ID: <ZB4Khv8PLs7aDOks@google.com>
Date:   Fri, 24 Mar 2023 13:39:34 -0700
From:   Sean Christopherson <seanjc@...gle.com>
To:     Mingwei Zhang <mizhang@...gle.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, linux-kselftest@...r.kernel.org,
        Jim Mattson <jmattson@...gle.com>,
        Venkatesh Srinivas <venkateshs@...gle.com>,
        Aaron Lewis <aaronlewis@...gle.com>,
        "Chang S. Bae" <chang.seok.bae@...el.com>,
        Chao Gao <chao.gao@...el.com>
Subject: Re: [PATCH v3 06/13] KVM: selftests: x86: Add the XFD check to
 IA32_XFD in #NM handler

On Tue, Feb 21, 2023, Mingwei Zhang wrote:
> Add an extra check to IA32_XFD to ensure the behavior is consistent with
> the AMX archtecture. In addition, repeat the checks across context switch
> to ensure the values of IA32_XFD and IA32_XFD_ERR are well preserved.
> 
> Signed-off-by: Mingwei Zhang <mizhang@...gle.com>
> ---
>  tools/testing/selftests/kvm/x86_64/amx_test.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/tools/testing/selftests/kvm/x86_64/amx_test.c b/tools/testing/selftests/kvm/x86_64/amx_test.c
> index ac49b14460b6..296c954dfd6d 100644
> --- a/tools/testing/selftests/kvm/x86_64/amx_test.c
> +++ b/tools/testing/selftests/kvm/x86_64/amx_test.c
> @@ -218,8 +218,10 @@ void guest_nm_handler(struct ex_regs *regs)
>  	GUEST_SYNC(7);
>  	GUEST_ASSERT((get_cr0() & X86_CR0_TS) == 0);
>  	GUEST_ASSERT(rdmsr(MSR_IA32_XFD_ERR) == XFEATURE_MASK_XTILEDATA);
> +	GUEST_ASSERT(rdmsr(MSR_IA32_XFD) & XFEATURE_MASK_XTILEDATA);

These should use ==, not &.  The test explicitly writes MSR_IA32_XFD, i.e. if
there are extra bits set then something is buggy.