linux-kernel - Re: [PATCH 1/4] KVM: selftests: x86: Fix an error in comment of amx

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Date:   Wed, 8 Feb 2023 01:13:02 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Mingwei Zhang <mizhang@...gle.com>
Cc:     kvm@...r.kernel.org, linux-kselftest@...r.kernel.org,
        linux-kernel@...r.kernel.org, Jim Mattson <jmattson@...gle.com>,
        Venkatesh Srinivas <venkateshs@...gle.com>,
        Aaron Lewis <aaronlewis@...gle.com>
Subject: Re: [PATCH 1/4] KVM: selftests: x86: Fix an error in comment of
 amx_test

On Tue, Jan 10, 2023, Mingwei Zhang wrote:
> After the execution of __tilerelease(), AMX component will be in INIT
> state. Therefore, execution of xsavec saving the AMX state into memory will

s/xsavec/XSAVEC

> cause the XSTATE_BV[18] cleared in xheader. However, the XCOMP_BV[18] will
> remain set. Fix the error in comment.
> 
> Cc: Jim Mattson <jmattson@...gle.com>
> Cc: Venkatesh Srinivas <venkateshs@...gle.com>
> Cc: Aaron Lewis <aaronlewis@...gle.com>
> 

No need for a blank line.

> Signed-off-by: Mingwei Zhang <mizhang@...gle.com>
> ---
>  tools/testing/selftests/kvm/x86_64/amx_test.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/tools/testing/selftests/kvm/x86_64/amx_test.c b/tools/testing/selftests/kvm/x86_64/amx_test.c
> index bd72c6eb3b67..16533949a189 100644
> --- a/tools/testing/selftests/kvm/x86_64/amx_test.c
> +++ b/tools/testing/selftests/kvm/x86_64/amx_test.c
> @@ -204,7 +204,7 @@ static void __attribute__((__flatten__)) guest_code(struct tile_config *amx_cfg,
>  	GUEST_SYNC(4);
>  	__tilerelease();
>  	GUEST_SYNC(5);
> -	/* bit 18 not in the XCOMP_BV after xsavec() */
> +	/* bit 18 not in the XSTATE_BV after xsavec() */

I would rather overhaul the entire comment, e.g.

	/* Verify XTILEDATA is not set in XSTATE_BV after XSAVEC */

I had to look at the definition of XFEATURE_XTILEDATA to verify that yes, indeed,
bit 18 is XTILEDATA.

As for xsavec() vs. XSAVE, IIUC the clearing of XCOMP_BV[18] is a side effect of
XSAVEC the instruction, not something extra done by xsavec() the function.

>  	set_xstatebv(xsave_data, XFEATURE_MASK_XTILEDATA);
>  	__xsavec(xsave_data, XFEATURE_MASK_XTILEDATA);
>  	GUEST_ASSERT((get_xstatebv(xsave_data) & XFEATURE_MASK_XTILEDATA) == 0);
> -- 
> 2.39.0.314.g84b9a713c41-goog
>