Re: [Xen-devel] [PATCH v4 11/24] x86/emul: Implement singlestep as a retire flag

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 01.12.16 at 17:55, <andrew.cooper3@xxxxxxxxxx> wrote:
> The behaviour of singlestep is to raise #DB after the instruction has been
> completed, but implementing it with inject_hw_exception() causes x86_emulate()
> to return X86EMUL_EXCEPTION, despite succesfully completing execution of the
> instruction, including register writeback.
> 
> Instead, use a retire flag to indicate singlestep, which causes x86_emulate()
> to return X86EMUL_OKAY.
> 
> Update all callers of x86_emulate() to use the new retire flag.  This fixes
> the behaviour of singlestep for shadow pagetable updates and mmcfg/mmio_ro
> intercepts, which previously discarded the exception.
> 
> With this change, all uses of X86EMUL_EXCEPTION from x86_emulate() are
> believed to have strictly fault semantics.
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> Reviewed-by: Paul Durrant <paul.durrant@xxxxxxxxxx>
> Acked-by: Tim Deegan <tim@xxxxxxx>

Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>


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