Re: [Xen-devel] [PATCH V2] x86/emulate: synchronize LOCKed instruction emulation

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 15.03.17 at 17:46, <rcojocaru@xxxxxxxxxxxxxxx> wrote:
> On 03/15/2017 06:30 PM, Jan Beulich wrote:
>>>>> On 15.03.17 at 17:04, <rcojocaru@xxxxxxxxxxxxxxx> wrote:
>>> ---
>>> Changes since V1:
>>>  - Added Andrew Cooper's credit, as he's kept the patch current
>>>    througout non-trivial code changes since the initial patch.
>>>  - Significantly more patch testing (with XenServer).
>>>  - Restricted lock scope.
>> 
>> Not by much, as it seems. In particular you continue to take the
>> lock even for instructions not accessing memory at all.
> 
> I'll take a closer look.
> 
>> Also, by "reworked" I did assume you mean converted to at least the
>> cmpxchg based model.
> 
> I haven't been able to follow the latest emulator changes closely, could
> you please clarify what you mean by "the cmpxchg model"? Thanks.

This is unrelated to any recent changes. The idea is to make the
->cmpxchg() hook actually behave like what its name says. It's
being used for LOCKed insn writeback already, and it could
therefore simply force a retry of the full instruction if the compare
part of it fails. It may need to be given another parameter, to
allow the hook function to tell LOCKed from "normal" uses.

Jan


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