* Avi Kivity <avi@xxxxxxxxxx> wrote: > On 06/15/2009 09:55 PM, H. Peter Anvin wrote: >> Ingo Molnar wrote: >> >>>> I wouldn't actually expect that, *as long as* there is >>>> serialization between the cr2 write and the cr2 read. >>>> >>> Well, is there any OS that heavily relies on cr2 writes and which >>> uses them from NMI context, and which CPU makers care about? >>> (Meaning: Windows, pretty much.) >>> >>> If not then i agree that in theory it should work fine, but in >>> practice we only know that we dont know the unknown risk here ;-) >>> >>> >> >> I think you can drop "uses them from NMI context" from that statement; >> writing to %cr2 is independent of the context. >> >> I can try to find out internally what Intel's position on writing >> %cr2 is, but it'll take a while; however, KVM should be able to >> tell you if any random OS uses %cr2 writes (as should a static >> disassembly of their kernel.) > > Linux is one such OS. When acting as a hypervisor it writes cr2 > to present its guests with their expected environment (any > hypervisor that uses virtualization extensions will of course need > to do this). Ah, it does save/restore it in svm_vcpu_run. VMX can do this via its context structure (without explicit CR manipulations in host space), right? Ingo -- To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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