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Re: [Xen-devel] shadow OOS and fast path are incompatible
| To: | Tim Deegan <Tim.Deegan@xxxxxxxxxx> |
|---|---|
| Subject: | Re: [Xen-devel] shadow OOS and fast path are incompatible |
| From: | Gianluca Guida <gianluca.guida@xxxxxxxxxxxxx> |
| Date: | Fri, 3 Jul 2009 11:20:21 +0200 |
| Cc: | Frank van der Linden <Frank.Vanderlinden@xxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx> |
| Delivery-date: | Fri, 03 Jul 2009 02:20:53 -0700 |
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About the read-only MMIO,
On Fri, Jul 3, 2009 at 10:50 AM, Tim Deegan<Tim.Deegan@xxxxxxxxxx> wrote:
> Yes. The fast-not-present path is safe without OOS because the changing
> L1 would have to be as a result of the guest writing it, which is a race
> on real hardware. The fast-MMIO path is OK even with OOS because it
> only caches present entries, but for proper safety we might want to
> avoid using fast-path MMIO if the guest maps MMIO space read-only (does
> anyone actually do that?)
That is still correct. The fast path gets only the gfn + offset and
pass it to the mmio handling code, that will check the permission by
using proper locks.
Gianluca
--
It was a type of people I did not know, I found them very strange and
they did not inspire confidence at all. Later I learned that I had been
introduced to electronic engineers.
E. W. Dijkstra
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