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 14.08.14 at 18:49, <andrew.cooper3@xxxxxxxxxx> wrote:
> On 14/08/14 17:43, Tian, Kevin wrote:
>>
>> but doing so just moves from one incomplete solution (where
>> read-modify-write is not treated as read-violation) to another
>> incomplete solution (where all writes are treated read-violation). If
>> there's actual usage relying on accurate read-violation information,
>> either solution doesn't work. So I don't see the value of this change.
>>
> 
> I would agree.  Anything using this information will have to have
> detailed knowledge of what the hardware is capable of reporting, to
> understand the information it has to hand.
> 
> I think Xen should faithfully pass on what hardware reports.  It will be
> more useful to the consumer than blurring the details like this.

Not if it's unreliable. Plus on x86 elsewhere write access implies
read access anyway. If you look at the draft patch I had sent
Tamas (which I intend to rebase on his series), you'll see that
there the change here is actually strictly needed.

Jan


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