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Re: [PATCH 2/2] KVM: x86: fix edge EOI and IOAPIC reconfig race

From Paolo Bonzini <pbonzini@redhat.com>
Newsgroups linux.kernel
Subject Re: [PATCH 2/2] KVM: x86: fix edge EOI and IOAPIC reconfig race
Date 2015-08-13 17:00 +0200
Message-ID <pX294-6rZ-9@gated-at.bofh.it> (permalink)
References <pX13j-4V5-3@gated-at.bofh.it> <pX13k-4V5-23@gated-at.bofh.it>
Organization linux.* mail to news gateway

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On 13/08/2015 15:46, Radim Krčmář wrote:
>  1) IOAPIC inject a vector from i8254
>  2) guest reconfigures that vector's VCPU and therefore eoi_exit_bitmap
>     on original VCPU gets cleared
>  3) guest's handler for the vector does EOI
>  4) KVM's EOI handler doesn't pass that vector to IOAPIC because it is
>     not in that VCPU's eoi_exit_bitmap
>  5) i8254 stops working
> 
> This creates an unwanted situation if the vector is reused by a
> non-IOAPIC source, but I think it is so rare that we don't want to make
> the solution more sophisticated. 

What happens if the vector is changed in step 2?
__kvm_ioapic_update_eoi won't match the redirection table entry.

How do you reproduce the bug?

Paolo
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Thread

[PATCH 0/2] KVM: x86: fix edge EOI and IOAPIC reconfig race Radim Krčmář <rkrcmar@redhat.com> - 2015-08-13 15:50 +0200
  [PATCH 1/2] KVM: x86: return bool from x86_ops.sync_pir_to_irr Radim Krčmář <rkrcmar@redhat.com> - 2015-08-13 15:50 +0200
  [PATCH 2/2] KVM: x86: fix edge EOI and IOAPIC reconfig race Radim Krčmář <rkrcmar@redhat.com> - 2015-08-13 15:50 +0200
    Re: [PATCH 2/2] KVM: x86: fix edge EOI and IOAPIC reconfig race Paolo Bonzini <pbonzini@redhat.com> - 2015-08-13 17:00 +0200
      Re: [PATCH 2/2] KVM: x86: fix edge EOI and IOAPIC reconfig race Radim Krčmář <rkrcmar@redhat.com> - 2015-08-14 10:40 +0200
        Re: [PATCH 2/2] KVM: x86: fix edge EOI and IOAPIC reconfig race Paolo Bonzini <pbonzini@redhat.com> - 2015-08-15 02:10 +0200

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