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Commit 4ae3cb3a authored by Lan Tianyu's avatar Lan Tianyu Committed by Paolo Bonzini
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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: default avatarLan Tianyu <tianyu.lan@intel.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent 7bfdf217

virt/kvm/kvm_main.c

+16 −2
Original line number Diff line number Diff line
@@ -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);