Re: switching from KVM guest to the host .... TLBs not present?

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Zhang, Xiantao wrote:
Yeah, that is very strange! I will check it tomorrow, and have to sleep now :-)

Hi Xiantao,

I think I got it!

We were calling local_irqs_disable() before calling down_read(), but
down_read() can sleep and so may return with local interrupts

I have reordered things so now we should be safe.

How does this patch look to you?


Reorder locking as down_read() may return with local interrupts enabled,
which means we could go into vti_vcpu_run() with interrupts enabled.

This caused random crashes on the Altix as the timer interrupt tried
to read a memory mapped clock source, for which the TLB had not yet been
reinstated in the exit, before ipsr was retored.

Signed-off-by: Jes Sorensen <jes@xxxxxxx>

 arch/ia64/kvm/kvm-ia64.c |   14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

Index: linux-2.6.git/arch/ia64/kvm/kvm-ia64.c
--- linux-2.6.git.orig/arch/ia64/kvm/kvm-ia64.c
+++ linux-2.6.git/arch/ia64/kvm/kvm-ia64.c
@@ -610,20 +610,22 @@
 	int r;
-	preempt_disable();
-	local_irq_disable();
 	if (signal_pending(current)) {
-		local_irq_enable();
-		preempt_enable();
 		r = -EINTR;
 		kvm_run->exit_reason = KVM_EXIT_INTR;
 		goto out;
+	/*
+	 * down_read() may sleep and return with interrupts enabled
+	 */
+	down_read(&vcpu->kvm->slots_lock);
+	preempt_disable();
+	local_irq_disable();
 	vcpu->guest_mode = 1;
-	down_read(&vcpu->kvm->slots_lock);
 	r = vti_vcpu_run(vcpu, kvm_run);
 	if (r < 0) {

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