Re: [Xen-devel] [PATCH] xen: provide pse36 cpuid bit

[Tim Deegan <tim@xxxxxxx>]

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.

Tim.

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