linux-kernel - Re: [PATCH v3 01/13] x86/fpu/xstate: Avoid getting xstate address of init_fpstate if fpstate contains the component

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Message-ID: <CAL715WKLQxxeyFqiKbKsUmQ8bZf2f=rwADyKj1ftgROA+dhpXg@mail.gmail.com>
Date:   Wed, 22 Feb 2023 10:40:12 -0800
From:   Mingwei Zhang <mizhang@...gle.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     "Chang S. Bae" <chang.seok.bae@...el.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        "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>,
        Chao Gao <chao.gao@...el.com>
Subject: Re: [PATCH v3 01/13] x86/fpu/xstate: Avoid getting xstate address of
 init_fpstate if fpstate contains the component

> > We have this [1]:
> >
> >       if (fpu_state_size_dynamic())
> >               mask &= (header.xfeatures | xinit->header.xcomp_bv);
> >
> > If header.xfeatures[18] = 0 then mask[18] = 0 because
> > xinit->header.xcomp_bv[18] = 0. Then, it won't hit that code. So, I'm
> > confused about the problem that you described here.
>
> Read the suggested changelog I wrote in my reply to Mingwei.
>
> TLDR:
>
>         xsave.header.xfeatures[18] = 1
>         xinit.header.xfeatures[18] = 0
>     ->  mask[18] = 1
>     ->  __raw_xsave_addr(xsave, 18)     <- Success
>     ->  __raw_xsave_addr(xinit, 18)     <- WARN
>
> Thanks,
>
>         tglx

Hi Thomas,

Thanks for the review and I will provide the next version separately
from the series, since this one is independent from the rest.

Chang: to reproduce this issue, you can simply run the amx_test in the
kvm selftest directory.

Thanks.
-Mingwei