linux-kernel - Re: [PATCH v2 2/7] KVM: selftests: x86: Fix an error in comment of amx

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Date:   Sun, 19 Feb 2023 17:58:40 +0000
From:   Mingwei Zhang <mizhang@...gle.com>
To:     Chao Gao <chao.gao@...el.com>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>, 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>,
        "Chang S. Bae" <chang.seok.bae@...el.com>
Subject: Re: [PATCH v2 2/7] KVM: selftests: x86: Fix an error in comment of
 amx_test

On Sun, Feb 19, 2023, Chao Gao wrote:
> On Tue, Feb 14, 2023 at 06:46:01PM +0000, 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
> >cause the xstate_bv[18] cleared in xheader. However, the xcomp_bv[18] will
> >remain set. Fix the error in comment. Also, update xsavec() to XSAVEC
> >because xcomp_bv[18] is set due to the instruction, not the function.
> >Finally, use XTILEDATA instead 'bit 18' in comments.
> >
> >Cc: Jim Mattson <jmattson@...gle.com>
> >Cc: Venkatesh Srinivas <venkateshs@...gle.com>
> >Cc: Aaron Lewis <aaronlewis@...gle.com>
> >Signed-off-by: Mingwei Zhang <mizhang@...gle.com>
> >---
> > tools/testing/selftests/kvm/x86_64/amx_test.c | 5 ++++-
> > 1 file changed, 4 insertions(+), 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 d506821a5a26..aac727ff7cf8 100644
> >--- a/tools/testing/selftests/kvm/x86_64/amx_test.c
> >+++ b/tools/testing/selftests/kvm/x86_64/amx_test.c
> >@@ -190,7 +190,10 @@ 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() */
> >+	/*
> >+	 * After XSAVEC, XTILEDATA is cleared in the xstate_bv but is set in
> >+	 * the xcomp_bv.
> >+	 */
> > 	xstate->header.xstate_bv = XFEATURE_MASK_XTILEDATA;
> > 	__xsavec(xstate, XFEATURE_MASK_XTILEDATA);
> > 	GUEST_ASSERT(!(xstate->header.xstate_bv & XFEATURE_MASK_XTILEDATA));
> 
> maybe it would be better to add another GUEST_ASSERT() to enforce that
> XTILEDATA is set in the xcomp_bv.

yeah. The check has been added in the 6th patch of the series, but I
think it is hard to see. I will reorder the change next to this one in
the next version.
> 
> >-- 
> >2.39.1.581.gbfd45094c4-goog
> >