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Re: [Xen-devel] [PATCH v8 2/4] x86/hvm: Treat non-instruction fetch nested page faults also as read violations

> From: Tim Deegan [mailto:tim@xxxxxxx]
> Sent: Thursday, August 28, 2014 3:14 AM
> At 15:40 +0200 on 19 Aug (1408459219), Tamas K Lengyel wrote:
> > As pointed out by Jan Beulich in
> http://lists.xen.org/archives/html/xen-devel/2014-08/msg01269.html:
> "Read-modify-write instructions absolutely need to be treated as read
> accesses, yet hardware doesn't guarantee to tell us so (they may surface as
> just write accesses)." This patch addresses the issue in both the VMX and the
> SVM side.
> >
> > VMX: Treat all write data access violations also as read violations (in
> addition to those that were already reported as read violations).
> > SVM: Refine the meaning of read data access violations to distinguish
> between read/write and instruction fetch access violations.
> >
> > With this patch both VMX and SVM specific nested page fault handling code
> reports violations the same way, thus abstracting the hardware specific
> behaviour from the layers above.
> >
> > Suggested-by: Jan Beulich <JBeulich@xxxxxxxx>
> > Signed-off-by: Tamas K Lengyel <tamas.lengyel@xxxxxxxxxxxx>
> > Reviewed-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
> Reviewed-by: Tim Deegan <tim@xxxxxxx>

As I commented earlier in another mail, I still think the right way is to
do the treatment in general place... 


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