Messages in this thread | | | Date | Fri, 25 Jan 2008 13:17:32 +0000 | Subject | Re: [PATCH UPDATE] x86: ignore spurious faults | From | Keir Fraser <> |
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On 25/1/08 10:19, "Andi Kleen" <ak@suse.de> wrote:
>> Whether this a problem in light of Xen spurious faults depends on whether >> NMI handlers touch dynamically-allocated data. > > How do you define dynamically-allocated data?
Anything that could have been a read-only pte or ldt page in a previous life with no intervening TLB flush. So get_free_page(), kmalloc(), vmalloc(), ...
Actually I think we are fine, now I think about it some more, because we only clear the software NMI-in-flight flag if the guest executes IRET via the hypervisor. Most Xen Linux guests only do IRET via the hypervisor when the current context is an NMI handler (additionally x86_64 also does so when returning to ring 3). Most importantly for this case, we will *not* IRET via the hypervisor when returning from a #PF context nested in an NMI context. Hence the NMI-in-flight flag will not be cleared, and guest virtual NMIs will not nest. So that's a relief!
-- Keir
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