Messages in this thread Patch in this message | | | From | Uros Bizjak <> | Subject | [PATCH] KVM: x86/mmu: Use try_cmpxchg64 in tdp_mmu_set_spte_atomic | Date | Wed, 18 May 2022 15:51:11 +0200 |
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Use try_cmpxchg64 instead of cmpxchg64 (*ptr, old, new) != old in tdp_mmu_set_spte_atomic. cmpxchg returns success in ZF flag, so this change saves a compare after cmpxchg (and related move instruction in front of cmpxchg). Also, remove explicit assignment to iter->old_spte when cmpxchg fails, this is what try_cmpxchg does implicitly.
Cc: Paolo Bonzini <pbonzini@redhat.com> Cc: Sean Christopherson <seanjc@google.com> Signed-off-by: Uros Bizjak <ubizjak@gmail.com> --- Patch requires commits 0aa7be05d83cc584da0782405e8007e351dfb6cc and c2df0a6af177b6c06a859806a876f92b072dc624 from tip.git --- arch/x86/kvm/mmu/tdp_mmu.c | 12 +----------- 1 file changed, 1 insertion(+), 11 deletions(-)
diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c index 922b06bf4b94..1ccc1a0f8123 100644 --- a/arch/x86/kvm/mmu/tdp_mmu.c +++ b/arch/x86/kvm/mmu/tdp_mmu.c @@ -633,7 +633,6 @@ static inline int tdp_mmu_set_spte_atomic(struct kvm *kvm, u64 new_spte) { u64 *sptep = rcu_dereference(iter->sptep); - u64 old_spte; /* * The caller is responsible for ensuring the old SPTE is not a REMOVED @@ -649,17 +648,8 @@ static inline int tdp_mmu_set_spte_atomic(struct kvm *kvm, * Note, fast_pf_fix_direct_spte() can also modify TDP MMU SPTEs and * does not hold the mmu_lock. */ - old_spte = cmpxchg64(sptep, iter->old_spte, new_spte); - if (old_spte != iter->old_spte) { - /* - * The page table entry was modified by a different logical - * CPU. Refresh iter->old_spte with the current value so the - * caller operates on fresh data, e.g. if it retries - * tdp_mmu_set_spte_atomic(). - */ - iter->old_spte = old_spte; + if (!try_cmpxchg64(sptep, &iter->old_spte, new_spte)) return -EBUSY; - } __handle_changed_spte(kvm, iter->as_id, iter->gfn, iter->old_spte, new_spte, iter->level, true); -- 2.35.1
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