Re: [Patch v4 2/4] Add SMEP handling when setting CR4

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On 05/31/2011 09:48 PM, Marcelo Tosatti wrote:
On Tue, May 31, 2011 at 09:05:35PM +0300, Avi Kivity wrote:
>  >>    	if (is_long_mode(vcpu)) {
>  >>    		if (!(cr4&   X86_CR4_PAE))
>  >>    			return 1;
>  >
>  >A new field in vcpu->arch.mmu.base_role for smep is required
>  >for shadow MMU (similar to nxe).
>
>  I plan to add that with my cr0.wp=0 fixup (it's only needed there, right?)

Sptes instantiated when cr4.smep = 0 should not be used when cr4.smep =
1, so no (unlikely that guest kernel executes user=1 code anyway, but
for consistency with other base_role flags).

Why not?  The sptes are interpreted exactly the same.

sptes are interpreted differently when efer.nxe=1 - if bit 63 is set, it will fault when nxe=0 and will not fault when nxe=1 (for non-fetch accesses). So we can't share those sptes.

OK then, you'll fix that.


Sure.  I'll post the patches as soon as this hits 'next'.

--
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.

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