Subject: Re: [PATCH 2/2] KVM: x86: fix edge EOI and IOAPIC reconfig race
To: =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= <rkrcmar@redhat.com>,
        linux-kernel@vger.kernel.org
References: <1439473570-13763-1-git-send-email-rkrcmar@redhat.com>
 <1439473570-13763-3-git-send-email-rkrcmar@redhat.com>
Cc: kvm@vger.kernel.org, Steve Rutherford <srutherford@google.com>,
        stable@vger.kernel.org
From: Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <55CCAF5D.8050204@redhat.com>
Date: Thu, 13 Aug 2015 16:53:17 +0200
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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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