diff options
| author | Andrew Jones <drjones@redhat.com> | 2017-04-26 23:32:24 +0300 |
|---|---|---|
| committer | Paolo Bonzini <pbonzini@redhat.com> | 2017-04-27 15:16:17 +0300 |
| commit | cde9af6e79046e12cd08d161139b1d5e57e9fbac (patch) | |
| tree | 2192140fe822f0805d3b766f3e277798e12445b0 | |
| parent | 6c6e8360b34d59d2f687a1649e61173742dbc891 (diff) | |
| download | linux-cde9af6e79046e12cd08d161139b1d5e57e9fbac.tar.xz | |
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>
| -rw-r--r-- | arch/x86/kvm/x86.c | 2 | ||||
| -rw-r--r-- | include/linux/kvm_host.h | 6 | ||||
| -rw-r--r-- | virt/kvm/kvm_main.c | 3 |
3 files changed, 7 insertions, 4 deletions
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 0936c3e2e51c..69fcee26f4da 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -6853,7 +6853,7 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu) /* * 1) We should set ->mode before checking ->requests. Please see - * the comment in kvm_make_all_cpus_request. + * the comment in kvm_vcpu_exiting_guest_mode(). * * 2) For APICv, we should set ->mode before checking PIR.ON. This * pairs with the memory barrier implicit in pi_test_and_set_on diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h index a805ddcb7eb0..84c5396564f7 100644 --- a/include/linux/kvm_host.h +++ b/include/linux/kvm_host.h @@ -270,6 +270,12 @@ struct kvm_vcpu { static inline int kvm_vcpu_exiting_guest_mode(struct kvm_vcpu *vcpu) { + /* + * The memory barrier ensures a previous write to vcpu->requests cannot + * be reordered with the read of vcpu->mode. It pairs with the general + * memory barrier following the write of vcpu->mode in VCPU RUN. + */ + smp_mb__before_atomic(); return cmpxchg(&vcpu->mode, IN_GUEST_MODE, EXITING_GUEST_MODE); } 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); |