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authorAndrew Jones <drjones@redhat.com>2017-04-26 22:32:24 +0200
committerPaolo Bonzini <pbonzini@redhat.com>2017-04-27 14:16:17 +0200
commitcde9af6e79046e12cd08d161139b1d5e57e9fbac (patch)
tree2192140fe822f0805d3b766f3e277798e12445b0 /virt
parent6c6e8360b34d59d2f687a1649e61173742dbc891 (diff)
KVM: add explicit barrier to kvm_vcpu_kick
kvm_vcpu_kick() must issue a general memory barrier prior to reading vcpu->mode in order to ensure correctness of the mutual-exclusion memory barrier pattern used with vcpu->requests. While the cmpxchg called from kvm_vcpu_kick(): kvm_vcpu_kick kvm_arch_vcpu_should_kick kvm_vcpu_exiting_guest_mode cmpxchg implies general memory barriers before and after the operation, that implication is only valid when cmpxchg succeeds. We need an explicit barrier for when it fails, otherwise a VCPU thread on its entry path that reads zero for vcpu->requests does not exclude the possibility the requesting thread sees !IN_GUEST_MODE when it reads vcpu->mode. kvm_make_all_cpus_request already had a barrier, so we remove it, as now it would be redundant. Signed-off-by: Andrew Jones <drjones@redhat.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Diffstat (limited to 'virt')
-rw-r--r--virt/kvm/kvm_main.c3
1 files changed, 0 insertions, 3 deletions
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 3772f7dcc72d..1efb07643035 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -183,9 +183,6 @@ bool kvm_make_all_cpus_request(struct kvm *kvm, unsigned int req)
kvm_make_request(req, vcpu);
cpu = vcpu->cpu;
- /* Set ->requests bit before we read ->mode. */
- smp_mb__after_atomic();
-
if (!(req & KVM_REQUEST_NO_WAKEUP))
kvm_vcpu_wake_up(vcpu);