Re: [PATCH v5 2/9] KVM: MMU: fix race between 'walk_addr' and 'fetch'

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On 07/06/2010 01:45 PM, Xiao Guangrong wrote:
'walk_addr' is out of mmu_lock's protection, so while we handle 'fetch',
then guest's mapping has modifited by other vcpu's write path, such as
invlpg, pte_write and other fetch path

Fixed by checking all level's mapping


@@ -319,22 +319,23 @@ static u64 *FNAME(fetch)(struct kvm_vcpu *vcpu, gva_t addr,
  		direct_access&= ~ACC_WRITE_MASK;

  	for_each_shadow_entry(vcpu, addr, iterator) {
+		bool nonpresent = false, last_mapping = false;
+

I don't like these two new variables, but no suggestion at the moment. I'll try to simplify this loop later.

One idea may be:

   while (level > walker.level) {
         handle indirect pages
   }
   while (level > hlevel) {
         handle direct pages
   }
   handle last spte

I'm worried that this change is too big for backporting, but no suggestions on how to make it smaller, so we'll have to accept it.

-		spte = __pa(sp->spt)
-			| PT_PRESENT_MASK | PT_ACCESSED_MASK
-			| PT_WRITABLE_MASK | PT_USER_MASK;
-		*sptep = spte;
+		if (nonpresent) {
+			spte = __pa(sp->spt)
+				| PT_PRESENT_MASK | PT_ACCESSED_MASK
+				| PT_WRITABLE_MASK | PT_USER_MASK;
+			*sptep = spte;
+			continue;
+		}

Should be __set_spte(), but this already exists, so can be in a later patch.

--
error compiling committee.c: too many arguments to function

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