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xen-devel
Re: [Xen-devel] [PATCH] xen: provide pse36 cpuid bit
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 ? PSE36 support for 32bit legacy mode
can be done in a seperate patch.
Christoph
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