Re: [Xen-devel] Fetching instructions after page-fault, near page boundary?

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

On 2 Jun 2006, at 18:20, Petersson, Mats wrote:

> > Just try re-executing the instruction (i.e. directly return
> > to the guest). If the page has become unmapped then the
> > processor should handle the fault on instruction fetch.
> Ok, that approach makes more sense than my silly ideas of counting
> instruction bytes... And hopefully the code that removed our very much
> needed page will eventually let us actually emulate the instruction at
> some point, without too many re-executions... ;-)
Bear in mind that we need to be able to inject page faults into the 
guest from the emulator anyway, for other reasons. For example, 
consider INSB/OUTSB -- the memory area being transferred to/from may be 
paged out. Current HVM MMIO code is rather lax about dealing with this 
(i.e., it doesn't -- it ignores error returns from gva_to_gpa(), which 
itself has a bogus error value anyway (0 is a valid pa)). Given we need 
the code, we may just want to inject faults for instruction-fetch 
errors too, but we do have a choice for those.
 -- Keir


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