• Andrew Jones's avatar
    KVM: add explicit barrier to kvm_vcpu_kick · cde9af6e
    Andrew Jones authored
    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: default avatarAndrew Jones <drjones@redhat.com>
    Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
    cde9af6e
x86.c 222 KB