linux-kernel - Re: [PATCH v4 0/2] x86/kvm/fpu: Fix guest migration bugs that can crash guest

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Message-ID: <CAJ6HWG66HZ7raAa+YK0UOGLF+4O3JnzbZ+a-0j8GNixOhLk9dA@mail.gmail.com>
Date:   Thu, 17 Feb 2022 15:08:29 -0300
From:   Leonardo Bras Soares Passos <leobras@...hat.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>,
        "Chang S. Bae" <chang.seok.bae@...el.com>,
        Andy Lutomirski <luto@...nel.org>,
        David Gilbert <dgilbert@...hat.com>,
        Peter Xu <peterx@...hat.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 0/2] x86/kvm/fpu: Fix guest migration bugs that can
 crash guest

On Thu, Feb 17, 2022 at 11:52 AM Paolo Bonzini <pbonzini@...hat.com> wrote:
>
> On 2/17/22 06:30, Leonardo Bras wrote:
> > This patchset comes from a bug I found during qemu guest migration from a
> > host with newer CPU to a host with an older version of this CPU, and thus
> > having less FPU features.
> >
> > When the guests were created, the one with less features is used as
> > config, so migration is possible.
> >
> > Patch 1 fix a bug that always happens during this migration, and is
> > related to the fact that xsave saves all feature flags, but xrstor does
> > not touch the PKRU flag. It also changes how fpstate->user_xfeatures
> > is set, going from kvm_check_cpuid() to the later called
> > kvm_vcpu_after_set_cpuid().
> >
> > Patch 2 removes kvm_vcpu_arch.guest_supported_xcr0 since it now
> > duplicates guest_fpu.fpstate->user_xfeatures. Some wrappers were
> > introduced in order to make it easier to read the replaced version.
> >
> > Patches were compile-tested, and could fix the bug found.
>
> Queued, thanks (for 5.17 of course)!  For patch 2, I renamed the
> function to kvm_guest_supported_xcr0.
>
> Paolo
>

That's great!
Thanks Paolo!