Re: [PATCH v5 07/14] nEPT: Add EPT tables support to paging_tmpl.h

[Paolo Bonzini <pbonzini@redhat.com>]

 On Aug 01 2013, Xiao Guangrong wrote:
> On 08/01/2013 03:42 PM, Gleb Natapov wrote:
> > On Thu, Aug 01, 2013 at 03:31:01PM +0800, Xiao Guangrong wrote:
> >> On 08/01/2013 03:18 PM, Xiao Guangrong wrote:
> >>  +#endif
> >>>>>
> >>>>> Hmm, why not use shadow_x_mask, shadow_user_mask instead? PT_WRITABLE_MASK
> >>>>> is also suitable for ept, i guess we can remove the "#if/#else/#endif" after
> >>>>> that.
> >>>>>
> >>>> shadow_x_mask and shadow_user_mask do not depend on guest paging mode,
> >>>> so cannot be used here. Since we have to use ifdefs anyway relying on
> >>>> VMX_EPT_WRITABLE_MASK == PT_WRITABLE_MASK is not necessary. Makes code
> >>>> easier to read.
> >>>
> >>> Oh, yes, you are right.
> >>>
> >>> Reviewed-by: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
> >>
> >> BTW, i notice the code in mmu.c uses PT64_NX_MASK to check the permission,
> >> i.e:
> >>
> >> static bool need_remote_flush(u64 old, u64 new)
> >> {
> >> 	if (!is_shadow_present_pte(old))
> >> 		return false;
> >> 	if (!is_shadow_present_pte(new))
> >> 		return true;
> >> 	if ((old ^ new) & PT64_BASE_ADDR_MASK)
> >> 		return true;
> >> 	old ^= PT64_NX_MASK;
> >> 	new ^= PT64_NX_MASK;
> >> 	return (old & ~new & PT64_PERM_MASK) != 0;
> >> }
> >>
> >> It checks shadow page table and the mask is wrong one nest ept spte.
> > So shadow_x_mask need to be used here, correct?
> 
> Yes. The code checks shadow page table which does not depend on guest mode. :)

The XOR should be with shadow_nx_mask, no?  And PT64_PERM_MASK
should include both shadow_x_mask and shadow_nx_mask, I think.

Paolo