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

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Message-ID: <CAL715WL9V8d-jvxkSALKQsMTgwDoyG-zE0g2tKd7FxihUhVGTA@mail.gmail.com>
Date:   Mon, 13 Feb 2023 10:57:56 -0800
From:   Mingwei Zhang <mizhang@...gle.com>
To:     Sean Christopherson <seanjc@...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, Feb 7, 2023 at 5:13 PM Sean Christopherson <seanjc@...gle.com> wrote:
>
> 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.

ack.
>
> > 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.

I see, that's why you asked me to use capital words.
>
> >       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
> >