Re: [Xen-devel] [PATCH v6 2/4] x86/hvm: Treat non-instruction fetch nested page faults also as read violations

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 15.08.14 at 18:33, <tamas.lengyel@xxxxxxxxxxxx> wrote:
>> 
>>
>>>>  Ah, no, clearly not: Again - read-modify-write instructions _have_
>>> to be reported as being reads and writes. Reporting simply writes
>>> as reads too is the smaller of the two "evils" here. If anything we
>>> could introduce a "maybe-read" flag that gets set when don't know
>>> for sure.
>>>
>>
>> I think an explicit comment in VMX and SVM code explaining why the bits
>> are set the way they are may be sufficient (I know this is mentioned in the
>> commit message but having it in the code is better IMO).
> 
> I can certainly do that if the consensus is to include the patch.

The patch is a necessary prerequisite for the patch that I sent you
earlier (which I'll rebase on top of yours as soon as yours reached a
state that can go in - which, afaic, is already the case), so it will
have to go in (as said in another reply, in the worst case with a
maybe-read flag instead of the current solution, but personally I
don't see a point to distinguish the two cases until a consumer
appears that can't tolerate plain writes to also be marked as being
reads).

Jan


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