Re: KVM: MMU: remove prefault from invlpg handler

[Avi Kivity <avi@redhat.com>]

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.