[PATCH 23/52] KVM: PPC: Book3S: PR: Fix signal check race

Alexander Graf
2012-01-13T14:31:26Z

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>
---
arch/powerpc/kvm/book3s_pr.c | 20 ++++++++++++++++++++
1 files changed, 20 insertions(+), 0 deletions(-)

diff --git a/arch/powerpc/kvm/book3s_pr.c b/arch/powerpc/kvm/book3s_pr.c
index 0c31507..2da6704 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;
--
1.6.0.2