From bed1d1dfc4a458d82bcd258082638cbba860190d Mon Sep 17 00:00:00 2001 From: Marcelo Tosatti Date: Fri, 4 Apr 2008 14:56:44 -0300 Subject: [PATCH] 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 Signed-off-by: Avi Kivity --- arch/x86/kvm/mmu.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c index 5c4c16662c68..c89bf230af67 100644 --- a/arch/x86/kvm/mmu.c +++ b/arch/x86/kvm/mmu.c @@ -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; } -- GitLab