On 06/13/2012 10:01 AM, Marcelo Tosatti wrote: > On Tue, Jun 12, 2012 at 10:23:47AM +0800, Xiao Guangrong wrote: >> On 06/12/2012 07:32 AM, Marcelo Tosatti wrote: >> >>> On Tue, May 29, 2012 at 02:49:14PM +0800, Xiao Guangrong wrote: >>>> This bit indicates whether the spte can be writable on MMU, that means >>>> the corresponding gpte is writable and the corresponding gfn is not >>>> protected by shadow page protection >>> >>> Why is this still necessary, now that only sptes of direct shadow pages >>> are updated locklessly? >>> >> >> >> Yes, but it is still needed, for nested npt/ept, we need protect >> the nested page tables. > > Sure, but shadowed L1 nested pagetables are not direct shadow pages. > > They are shadows of L1 nested pagetables. > > Checking sp->direct should be enough (instead of the flags). > Hi Marcelo, I think it is not enough, for example: - In host (L0), spte1 is pointing to gfn1, spte1 is a direct spte. - in L1, L1 guest is using gfn1 in L1's ept page table for L2 guest, so, in host, we have a indirect spte (named spte2) whose sp->gfn = gfn1. Since spte2 is a indirect spte, we need protect it, so, we walk all gfn1's rmaps, spte1 will be found, then, we write-protect on spte1 to track L1 modifying gfn1. In this case, spte1 is direct but need write-protect. :) -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
