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authorLan Tianyu <tianyu.lan@intel.com>2016-03-13 11:10:28 +0800
committerPaolo Bonzini <pbonzini@redhat.com>2016-03-22 16:38:33 +0100
commit4ae3cb3a2551b41f22284f713e7d5e2b61a85c1d (patch)
tree153de5718a4688050cd3911a7442431a81620926 /virt/kvm
parent7bfdf2177812c30928bea3fc8bc86b9dea236f65 (diff)
downloadlinux-4ae3cb3a2551b41f22284f713e7d5e2b61a85c1d.tar.gz
KVM: Replace smp_mb() with smp_load_acquire() in the kvm_flush_remote_tlbs()
smp_load_acquire() is enough here and it's cheaper than smp_mb(). Adding a comment about reusing memory barrier of kvm_make_all_cpus_request() here to keep order between modifications to the page tables and reading mode. Signed-off-by: Lan Tianyu <tianyu.lan@intel.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Diffstat (limited to 'virt/kvm')
-rw-r--r--virt/kvm/kvm_main.c18
1 files changed, 16 insertions, 2 deletions
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 402590dfcf9b..4fd482fb9260 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -191,9 +191,23 @@ bool kvm_make_all_cpus_request(struct kvm *kvm, unsigned int req)
#ifndef CONFIG_HAVE_KVM_ARCH_TLB_FLUSH_ALL
void kvm_flush_remote_tlbs(struct kvm *kvm)
{
- long dirty_count = kvm->tlbs_dirty;
+ /*
+ * Read tlbs_dirty before setting KVM_REQ_TLB_FLUSH in
+ * kvm_make_all_cpus_request.
+ */
+ long dirty_count = smp_load_acquire(&kvm->tlbs_dirty);
- smp_mb();
+ /*
+ * We want to publish modifications to the page tables before reading
+ * mode. Pairs with a memory barrier in arch-specific code.
+ * - x86: smp_mb__after_srcu_read_unlock in vcpu_enter_guest
+ * and smp_mb in walk_shadow_page_lockless_begin/end.
+ * - powerpc: smp_mb in kvmppc_prepare_to_enter.
+ *
+ * There is already an smp_mb__after_atomic() before
+ * kvm_make_all_cpus_request() reads vcpu->mode. We reuse that
+ * barrier here.
+ */
if (kvm_make_all_cpus_request(kvm, KVM_REQ_TLB_FLUSH))
++kvm->stat.remote_tlb_flush;
cmpxchg(&kvm->tlbs_dirty, dirty_count, 0);