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KVM: MMU: prepopulate guest pages after write-protecting

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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>
This commit is contained in:
Marcelo Tosatti 2008-04-04 14:56:44 -03:00 committed by Avi Kivity
parent fcd6dbac92
commit bed1d1dfc4
1 changed files with 1 additions and 1 deletions
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2
arch/x86/kvm/mmu.c
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@ -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;
}