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

Gleb Natapov
2013-08-01T07:56:34Z

On Thu, Aug 01, 2013 at 03:51:35PM +0800, 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. :)
>
Yes, good catch. It would have been hard to find when hit on practice.
Will add separate patch to fix that after you review the reset of the
series :)

--
Gleb.