Re: [Xen-devel] [PATCH v2] x86/hvm: fix interaction between internal and external emulation

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 28.11.17 at 15:05, <paul.durrant@xxxxxxxxxx> wrote:
> A call to handle_hvm_io_completion() is needed for completing I/O
> that requires external emulation. Such completion should be requested when
> hvm_vcpu_io_need_completion() returns true after hvm_emulate_once() has
> completed. This is indicative of the underlying I/O emulation having
> returned X86EMUL_RETRY and hence a re-emulation of the instruction is
> needed to pick up the result of the I/O.
> 
> A call to handle_hvm_io_completion() is NOT needed when the underlying
> I/O has not returned X86EMUL_RETRY since there will be no result to pick
> up. Hence it bogus to request such completion when mmio_retry is set,
> since this can only happen if the underlying I/O emulation has returned
> X86EMUL_OKAY (meaning the I/O has completed successfully).
> 
> Reported-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> Signed-off-by: Paul Durrant <paul.durrant@xxxxxxxxxx>
> Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>

Hmm, I notice Paul didn't Cc you on this one - despite it getting late,
this is still something to be considered for 4.10. It's certainly going
to be a backporting candidate.

Jan


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