[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH] xen: provide pse36 cpuid bit
At 15:53 +0100 on 28 Oct (1319817196), Tim Deegan wrote: > At 16:20 +0200 on 28 Oct (1319818819), Christoph Egger wrote: > > On 10/27/11 17:30, Keir Fraser wrote: > > >On 27/10/2011 16:15, "Tim Deegan"<tim@xxxxxxx> wrote: > > > > > >>If you mean this: > > >> > > >> * PSE disabled / PSE36 > > >> * We don't support any modes other than PSE enabled, PSE36 disabled. > > >> * Neither of those would be hard to change, but we'd need to be able to > > >> * deal with shadows made in one mode and used in another. > > >> > > >>the worry was that we'd need a whole nother shadow mode to handle the > > >>case where one VCPU was in normal 32-bit and another was in PSE36 (since > > >>they can't share shadows). > > >> > > >>As it happens the current code does detect PSE-disabled in shadow mode > > >>but just DTRT for the current VCPU, so a mix of PSE-enabled and > > >>PSE-disabled VCPUs will get unpredicatble results from shadow > > >>pagetables. :( > > >> > > >>Which means that supporting PSE36 to the same degree (i.e. assuming all > > >>VCPUs behave the same, or if they don't they don't share pagetables) > > >>would be OK too. :) > > > > > >Ah, I see. Yes, I guessed it would be supported to just the same degree as > > >'basic' PSE. The likelihood of pagetables being shared across different > > >pagetable-related CR4 settings? Not great, we hope. :-) > > > > Is the patch acceptable as it is ? > > I'll put together a patch with basic PSE36 support next week. I don't > think we're in a terrible hurry to check in the CPUID change before then. Supporting PSE36 turned out to be trickier than I had thought - the trick in the guest-pagetable walker of making up an l1e with the equivalent semantics to the PSE l2e doesn't work for PSE36 because there isn't space for the extra address bits in a 32bit l1e. :( I didn't fancy changing that interface right now because it would need a fair bit of fixing up in the shadow code, but I might come back to it when I have more time. In the meantime I've applied Christoph's patch. Cheers, Tim. _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-devel
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