On 25/03/2016 14:48, Xiao Guangrong wrote:
>>>
>>
>> This patch and the previous one are basically redoing commit
>> 0a47cd85833e ("KVM: MMU: Fix ubsan warnings", 2016-03-04). While you
>> find your version easier to understand, I of course find mine easier.
>>
>> Rather than getting stuck in a ko fight, the solution is to stick with
>> the code in KVM and add comments. I'll give it a try...
>
> If you do not like this one, we can just make the .index is
> [PT64_ROOT_LEVEL - 1] and keep the sentinel in .parents[], that little
> change and nice code shape.
I suppose you'd have something like this then:
diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 70e95d097ef1..15e1735a2e3a 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -1980,7 +1980,7 @@ static bool kvm_sync_pages(struct kvm_vcpu *vcpu, gfn_t gfn,
struct mmu_page_path {
struct kvm_mmu_page *parent[PT64_ROOT_LEVEL];
- unsigned int idx[PT64_ROOT_LEVEL];
+ unsigned int idx[PT64_ROOT_LEVEL-1];
};
#define for_each_sp(pvec, sp, parents, i) \
@@ -2037,13 +2037,14 @@ static void mmu_pages_clear_parents(struct mmu_page_path *parents)
{
struct kvm_mmu_page *sp;
unsigned int level = 0;
+ unsigned int idx;
do {
- unsigned int idx = parents->idx[level];
sp = parents->parent[level];
- if (!sp)
+ if (!sp || WARN_ON(level == PT64_ROOT_LEVEL-1))
return;
+ idx = parents->idx[level];
WARN_ON(idx == INVALID_INDEX);
clear_unsync_child_bit(sp, idx);
level++;
By making the arrays the same size, the effect of the sentinel seems
clearer to me. It doesn't seem worth 4 bytes (and strictly speaking
those 4 bytes would be there anyway due to padding)...
Paolo
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