Re: [PATCH v2 3/3] Reenter guest after instruction emulation failure if emulation was due to access to non-mmio address.

[Avi Kivity <avi@redhat.com>]

On 07/08/2010 12:41 PM, Gleb Natapov wrote:
> When shadow pages are in use sometimes KVM try to emulate an instruction
> when it accesses a shadowed page. If emulation fails KVM un-shadows the
> page and reenter guest to allow vcpu to execute the instruction. If page
> is not in shadow page hash KVM assumes that this was attempt to do MMIO
> and reports emulation failure to userspace since there is no way to fix
> the situation. This logic has a race though. If two vcpus tries to write
> to the same shadowed page simultaneously both will enter emulator, but
> only one of them will find the page in shadow page hash since the one who
> founds it also removes it from there, so another cpu will report failure
> to userspace and will abort the guest.
>
> Fix this by checking (in addition to checking shadowed page hash) that
> page that caused the emulation belongs to valid memory slot. If it is
> then reenter the guest to allow vcpu to reexecute the instruction.
>
>    

Applied, thanks.

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