KVM: PPC: Book3S: PR: Fix signal check race

As Scott put it:

> If we get a signal after the check, we want to be sure that we don't
> receive the reschedule IPI until after we're in the guest, so that it
> will cause another signal check.

we need to have interrupts disabled from the point we do signal_check()
all the way until we actually enter the guest.

This patch fixes potential signal loss races.

Reported-by: Scott Wood <scottwood@freescale.com>
Signed-off-by: Alexander Graf <agraf@suse.de>
Signed-off-by: Avi Kivity <avi@redhat.com>

1 files changed, 20 insertions, 0 deletions

diff --git a/arch/powerpc/kvm/book3s_pr.c b/arch/powerpc/kvm/book3s_pr.c
index 0c31507be908..2da670405727 100644
--- a/arch/powerpc/kvm/book3s_pr.c
+++ b/arch/powerpc/kvm/book3s_pr.c
@@ -51,6 +51,8 @@ static int kvmppc_handle_ext(struct kvm_vcpu *vcpu, unsigned int exit_nr,
 #define MSR_USER32 MSR_USER
 #define MSR_USER64 MSR_USER
 #define HW_PAGE_SIZE PAGE_SIZE
+#define __hard_irq_disable local_irq_disable
+#define __hard_irq_enable local_irq_enable
 #endif
 
 void kvmppc_core_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
@@ -776,7 +778,16 @@ program_interrupt:
                 /* To avoid clobbering exit_reason, only check for signals if
                  * we aren't already exiting to userspace for some other
                  * reason. */
+
+                /*
+                 * Interrupts could be timers for the guest which we have to
+                 * inject again, so let's postpone them until we're in the guest
+                 * and if we really did time things so badly, then we just exit
+                 * again due to a host external interrupt.
+                 */
+                __hard_irq_disable();
                 if (signal_pending(current)) {
+                        __hard_irq_enable();
 #ifdef EXIT_DEBUG
                         printk(KERN_EMERG "KVM: Going back to host\n");
 #endif
@@ -959,8 +970,17 @@ int kvmppc_vcpu_run(struct kvm_run *kvm_run, struct kvm_vcpu *vcpu)
 
         kvmppc_core_prepare_to_enter(vcpu);
 
+        /*
+         * Interrupts could be timers for the guest which we have to inject
+         * again, so let's postpone them until we're in the guest and if we
+         * really did time things so badly, then we just exit again due to
+         * a host external interrupt.
+         */
+        __hard_irq_disable();
+
         /* No need to go into the guest when all we do is going out */
         if (signal_pending(current)) {
+                __hard_irq_enable();
                 kvm_run->exit_reason = KVM_EXIT_INTR;
                 ret = -EINTR;
                 goto out;