Commit bed1d1df authored Apr 04, 2008 by Marcelo Tosatti Committed by Avi Kivity Apr 27, 2008

KVM: MMU: prepopulate guest pages after write-protecting



Zdenek reported a bug where a looping "dmsetup status" eventually hangs
on SMP guests.

The problem is that kvm_mmu_get_page() prepopulates the shadow MMU
before write protecting the guest page tables. By doing so, it leaves a
window open where the guest can mark a pte as present while the host has
shadow cached such pte as "notrap". Accesses to such address will fault
in the guest without the host having a chance to fix the situation.

Fix by moving the write protection before the pte prefetch.

Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Avi Kivity <avi@qumranet.com>

parent fcd6dbac

arch/x86/kvm/mmu.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -852,9 +852,9 @@ static struct kvm_mmu_page kvm_mmu_get_page(struct kvm_vcpu vcpu,
		sp->gfn = gfn;
		sp->role = role;
		hlist_add_head(&sp->hash_link, bucket);
		vcpu->arch.mmu.prefetch_page(vcpu, sp);
		if (!metaphysical)
		rmap_write_protect(vcpu->kvm, gfn);
		vcpu->arch.mmu.prefetch_page(vcpu, sp);
		return sp;
		}

Admin message