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

[Tim Deegan <tim@xxxxxxx>]

At 09:33 -0700 on 23 Nov (1479893609), Jan Beulich wrote:
> >>> 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.

Oh right.  In that case AFAICS neither invocation of x86_emulate() in
shadow/multi.c needs any adjustment.

Tim.

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