Re: [Xen-devel] [PATCH 06/15] x86/emul: Rework emulator event injection

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 23.11.16 at 17:19, <tim@xxxxxxx> wrote:
> Hi,
> 
> At 15:38 +0000 on 23 Nov (1479915529), Andrew Cooper wrote:
>> The emulator needs to gain an understanding of interrupts and exceptions
>> generated by its actions.
>> 
>> Move hvm_emulate_ctxt.{exn_pending,trap} into struct x86_emulate_ctxt so 
> they
>> are visible to the emulator.  This removes the need for the
>> inject_{hw,sw}_interrupt() hooks, which are dropped and replaced with
>> x86_emul_{hw_exception,software_event}() instead.
>> 
>> The shadow pagetable and PV uses of x86_emulate() previously failed with
>> X86EMUL_UNHANDLEABLE due to the lack of inject_*() hooks, but this behaviour
>> has subtly changed.  Adjust the return value checking to cause a pending 
> event
>> to fall back into the previous codepath.
>> 
>> No overall functional change.
> 
> AIUI this does have a change in the shadow callers in the case where
> the emulated instruction would inject an event.  Previously we would
> have failed the emulation, perhaps unshadowed something, and returned
> to the guest to retry.
> 
> Now the emulator records the event in the context struct, updates the
> register state and returns success, so we'll return on the *next*
> instruction.  I think that's OK, though.

Not exactly - instead of success, X86EMUL_EXCEPTION is being
returned, which would suppress register updates. Also I don't
think continuing on the next instruction would be okay, as we'd
then basically have skipped the one having caused the (not
delivered) exception.

Jan


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