]> pilppa.com Git - linux-2.6-omap-h63xx.git/commitdiff
KVM: MMU: prepopulate guest pages after write-protecting
authorMarcelo Tosatti <mtosatti@redhat.com>
Fri, 4 Apr 2008 17:56:44 +0000 (14:56 -0300)
committerAvi Kivity <avi@qumranet.com>
Sun, 27 Apr 2008 09:00:58 +0000 (12:00 +0300)
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>
arch/x86/kvm/mmu.c

index 5c4c16662c6831752412c024a83ff9522454dac9..c89bf230af67bf4e3be4c974738a766eb870b2f6 100644 (file)
@@ -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;
 }