Use try_cmpxchg64 instead of cmpxchg64 (*ptr, old, new) != old in
fast_pf_fix_direct_spte. cmpxchg returns success in ZF flag, so this
change saves a compare after cmpxchg (and related move instruction
in front of cmpxchg).
Signed-off-by: Uros Bizjak <[email protected]>
Cc: Paolo Bonzini <[email protected]>
Cc: Sean Christopherson <[email protected]>
Cc: Vitaly Kuznetsov <[email protected]>
Cc: Wanpeng Li <[email protected]>
Cc: Jim Mattson <[email protected]>
Cc: Joerg Roedel <[email protected]>
---
The patch is against tip tree.
---
arch/x86/kvm/mmu/mmu.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 311e4e1d7870..347bfd8bc5a3 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -3073,7 +3073,7 @@ fast_pf_fix_direct_spte(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault,
*
* Compare with set_spte where instead shadow_dirty_mask is set.
*/
- if (cmpxchg64(sptep, old_spte, new_spte) != old_spte)
+ if (!try_cmpxchg64(sptep, &old_spte, new_spte))
return false;
if (is_writable_pte(new_spte) && !is_writable_pte(old_spte))
--
2.35.3
Queued, thanks.
Paolo