On 12/05/2009 06:57 PM, Avi Kivity wrote:
Looks like we considered this, since kvm_read_guest_atomic() is only
needed if inside the spinlock, but some other change moved the
spin_unlock() upwards. Will investigate history.
No, the bug was there from day one (and survived a year):
+ spin_lock(&vcpu->kvm->mmu_lock);
walk_shadow(&walker.walker, vcpu, gva);
+ spin_unlock(&vcpu->kvm->mmu_lock);
+ if (walker.pte_gpa == -1)
+ return;
+ if (kvm_read_guest_atomic(vcpu->kvm, walker.pte_gpa, &gpte,
+ sizeof(pt_element_t)))
+ return;
+ if (is_present_pte(gpte) && (gpte & PT_ACCESSED_MASK)) {
+ if (mmu_topup_memory_caches(vcpu))
+ return;
+ kvm_mmu_pte_write(vcpu, walker.pte_gpa, (const u8 *)&gpte,
+ sizeof(pt_element_t), 0);
+ }
--
Do not meddle in the internals of kernels, for they are subtle and quick to panic.
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