From 982b3394dd23eec6e5a2f7871238435a167b63cc Mon Sep 17 00:00:00 2001 From: Takuya Yoshikawa Date: Tue, 12 Mar 2013 17:45:30 +0900 Subject: [PATCH] KVM: x86: Optimize mmio spte zapping when creating/moving memslot When we create or move a memory slot, we need to zap mmio sptes. Currently, zap_all() is used for this and this is causing two problems: - extra page faults after zapping mmu pages - long mmu_lock hold time during zapping mmu pages For the latter, Marcelo reported a disastrous mmu_lock hold time during hot-plug, which made the guest unresponsive for a long time. This patch takes a simple way to fix these problems: do not zap mmu pages unless they are marked mmio cached. On our test box, this took only 50us for the 4GB guest and we did not see ms of mmu_lock hold time any more. Note that we still need to do zap_all() for other cases. So another work is also needed: Xiao's work may be the one. Reviewed-by: Marcelo Tosatti Signed-off-by: Takuya Yoshikawa Signed-off-by: Gleb Natapov --- arch/x86/include/asm/kvm_host.h | 1 + arch/x86/kvm/mmu.c | 18 ++++++++++++++++++ arch/x86/kvm/x86.c | 2 +- 3 files changed, 20 insertions(+), 1 deletion(-) diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h index 9b75cae83d10..3f205c6cde59 100644 --- a/arch/x86/include/asm/kvm_host.h +++ b/arch/x86/include/asm/kvm_host.h @@ -767,6 +767,7 @@ void kvm_mmu_write_protect_pt_masked(struct kvm *kvm, struct kvm_memory_slot *slot, gfn_t gfn_offset, unsigned long mask); void kvm_mmu_zap_all(struct kvm *kvm); +void kvm_mmu_zap_mmio_sptes(struct kvm *kvm); unsigned int kvm_mmu_calculate_mmu_pages(struct kvm *kvm); void kvm_mmu_change_mmu_pages(struct kvm *kvm, unsigned int kvm_nr_mmu_pages); diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c index de45ec195346..c1a9b7b08ab7 100644 --- a/arch/x86/kvm/mmu.c +++ b/arch/x86/kvm/mmu.c @@ -4189,6 +4189,24 @@ restart: spin_unlock(&kvm->mmu_lock); } +void kvm_mmu_zap_mmio_sptes(struct kvm *kvm) +{ + struct kvm_mmu_page *sp, *node; + LIST_HEAD(invalid_list); + + spin_lock(&kvm->mmu_lock); +restart: + list_for_each_entry_safe(sp, node, &kvm->arch.active_mmu_pages, link) { + if (!sp->mmio_cached) + continue; + if (kvm_mmu_prepare_zap_page(kvm, sp, &invalid_list)) + goto restart; + } + + kvm_mmu_commit_zap_page(kvm, &invalid_list); + spin_unlock(&kvm->mmu_lock); +} + static int mmu_shrink(struct shrinker *shrink, struct shrink_control *sc) { struct kvm *kvm; diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 61a5bb60af86..d3c478742e2c 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -6991,7 +6991,7 @@ void kvm_arch_commit_memory_region(struct kvm *kvm, * mmio sptes. */ if ((change == KVM_MR_CREATE) || (change == KVM_MR_MOVE)) { - kvm_mmu_zap_all(kvm); + kvm_mmu_zap_mmio_sptes(kvm); kvm_reload_remote_mmus(kvm); } } -- 2.34.1