3.2.85-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: Ignacio Alvarado <ikalvarado@xxxxxxxxxx> commit 1650b4ebc99da4c137bfbfc531be4a2405f951dd upstream. Function user_notifier_unregister should be called only once for each registered user notifier. Function kvm_arch_hardware_disable can be executed from an IPI context which could cause a race condition with a VCPU returning to user mode and attempting to unregister the notifier. Signed-off-by: Ignacio Alvarado <ikalvarado@xxxxxxxxxx> Fixes: 18863bdd60f8 ("KVM: x86 shared msr infrastructure") Reviewed-by: Paolo Bonzini <pbonzini@xxxxxxxxxx> Signed-off-by: Radim Krčmář <rkrcmar@xxxxxxxxxx> Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx> --- arch/x86/kvm/x86.c | 13 +++++++++++-- 1 file changed, 11 insertions(+), 2 deletions(-) --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -172,7 +172,18 @@ static void kvm_on_user_return(struct us struct kvm_shared_msrs *locals = container_of(urn, struct kvm_shared_msrs, urn); struct kvm_shared_msr_values *values; + unsigned long flags; + /* + * Disabling irqs at this point since the following code could be + * interrupted and executed through kvm_arch_hardware_disable() + */ + local_irq_save(flags); + if (locals->registered) { + locals->registered = false; + user_return_notifier_unregister(urn); + } + local_irq_restore(flags); for (slot = 0; slot < shared_msrs_global.nr; ++slot) { values = &locals->values[slot]; if (values->host != values->curr) { @@ -180,8 +191,6 @@ static void kvm_on_user_return(struct us values->curr = values->host; } } - locals->registered = false; - user_return_notifier_unregister(urn); } static void shared_msr_update(unsigned slot, u32 msr)