linux-kernel - Re: Re: [PATCH] KVM: x86: Fix uninitialized eoi_exit_bitmap usage in vcpu_load_eoi

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Message-ID: <567b276444f841519e42c91f43f5acd7@jd.com>
Date:   Mon, 15 Nov 2021 12:41:00 +0000
From:   黄乐 <huangle1@...com>
To:     "vkuznets@...hat.com" <vkuznets@...hat.com>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>
CC:     "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: Re: [PATCH] KVM: x86: Fix uninitialized eoi_exit_bitmap usage in
 vcpu_load_eoi_exitmap()

> 黄乐 <huangle1@...com> writes:
> 
> > In vcpu_load_eoi_exitmap(), currently the eoi_exit_bitmap[4] array is
> > initialized only when Hyper-V context is available, in other path it is
> > just passed to kvm_x86_ops.load_eoi_exitmap() directly from on the stack,
> > which would cause unexpected interrupt delivery/handling issues, e.g. an
> > *old* linux kernel that relies on PIT to do clock calibration on KVM might
> > randomly fail to boot.
> >
> > Fix it by passing ioapic_handled_vectors to load_eoi_exitmap() when Hyper-V
> > context is not available.
> >
> > Signed-off-by: Huang Le <huangle1@...com>
> 
> Fixes: f2bc14b69c38 ("KVM: x86: hyper-v: Prepare to meet unallocated Hyper-V context")
> Cc: stable@...r.kernel.org

Commit f2bc14b69c38 is not in stable tree I guess, it was merged in from 5.12,
do we still need Cc this patch to stable maintainers?

> 
> > ---
> > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> > index dc7eb5fddfd3..0699832504c9 100644
> > --- a/arch/x86/kvm/x86.c
> > +++ b/arch/x86/kvm/x86.c
> > @@ -9547,11 +9547,14 @@ static void vcpu_load_eoi_exitmap(struct kvm_vcpu *vcpu)
> >        if (!kvm_apic_hw_enabled(vcpu->arch.apic))
> >                return;
> > 
> > -     if (to_hv_vcpu(vcpu))
> > -             bitmap_or((ulong *)eoi_exit_bitmap,
> > -                       vcpu->arch.ioapic_handled_vectors,
> > -                       to_hv_synic(vcpu)->vec_bitmap, 256);
> > +     if (!to_hv_vcpu(vcpu)) {
> > +             static_call(kvm_x86_load_eoi_exitmap)(
> > +                     vcpu, (u64 *)vcpu->arch.ioapic_handled_vectors);
> > +             return;
> > +     }
> > 
> > +     bitmap_or((ulong *)eoi_exit_bitmap, vcpu->arch.ioapic_handled_vectors,
> > +               to_hv_synic(vcpu)->vec_bitmap, 256);
> >        static_call(kvm_x86_load_eoi_exitmap)(vcpu, eoi_exit_bitmap);
> >  }
> > 
> 
> Reviewed-by: Vitaly Kuznetsov <vkuznets@...hat.com>
> 
> My personal preference, however, would be to keep 'if
> (to_hv_vcpu(vcpu))' check and not invert it, i.e.:
> 
>         if (to_hv_vcpu(vcpu)) {
>                 bitmap_or((ulong *)eoi_exit_bitmap,
>                  vcpu->arch.ioapic_handled_vectors,
>                  to_hv_synic(vcpu)->vec_bitmap, 256);
>                 static_call(...)(vcpu, eoi_exit_bitmap)
>                 return;
>         }
> 
>         static_call(...)(vcpu, (u64 *)vcpu->arch.ioapic_handled_vectors);
> 
> to slightly reduce the code churn but it doesn't matter much.

Got it.  Will send an updated one later.  Thanks for suggestion!

> 
> Thanks!
> 
> --
> Vitaly