Re: KVM: MMU: only write protect mappings at pagetable level

[Avi Kivity <avi@redhat.com>]

On 12/22/2010 01:12 PM, Marcelo Tosatti wrote:
> On Wed, Dec 22, 2010 at 01:07:23PM +0200, Avi Kivity wrote:
> >  On 12/22/2010 01:01 PM, Marcelo Tosatti wrote:
> >  >If a pagetable contains a writeable large spte, all of its sptes will be
> >
> >  non-writeable
> >
> >  >write protected, including non-leaf ones, leading to endless pagefaults.
> >  >
> >  >Do not write protect pages above PT_PAGE_TABLE_LEVEL, as the spte fault
> >  >paths assume non-leaf sptes are writable.
> >  >
> >  >Signed-off-by: Marcelo Tosatti<mtosatti@redhat.com>
> >  >
> >  >diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
> >  >index c3853d5..c716ff8 100644
> >  >--- a/arch/x86/kvm/mmu.c
> >  >+++ b/arch/x86/kvm/mmu.c
> >  >@@ -3442,6 +3442,9 @@ void kvm_mmu_slot_remove_write_access(struct kvm *kvm, int slot)
> >  >   		if (!test_bit(slot, sp->slot_bitmap))
> >  >   			continue;
> >  >
> >  >+		if (sp->role.level != PT_PAGE_TABLE_LEVEL)
> >  >+			continue;
> >  >+
> >  >   		pt = sp->spt;
> >  >   		for (i = 0; i<   PT64_ENT_PER_PAGE; ++i)
> >  >   			/* avoid RMW */
> >
> >  But what about large leaf sptes?  Don't we want to write protect, or
> >  perhaps drop them?
> >
> >  I think write-protecting leaf sptes and ignoring nonleaf sptes should work.
>
> When dirty logging is enabled large sptes are nuked and creation of new
> ones is not allowed. So i don't see the need?

Where does this nuking happen?

All I see is the call to kvm_mmu_slot_remove_write_access().

-- 
error compiling committee.c: too many arguments to function