[PATCH 5.15 166/297] KVM: x86: hyper-v: Dont auto-enable stimer on write from user-space

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5.15-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Nicolas Saenz Julienne <nsaenz@xxxxxxxxxx>

commit d6800af51c76b6dae20e6023bbdc9b3da3ab5121 upstream.

Don't apply the stimer's counter side effects when modifying its
value from user-space, as this may trigger spurious interrupts.

For example:
 - The stimer is configured in auto-enable mode.
 - The stimer's count is set and the timer enabled.
 - The stimer expires, an interrupt is injected.
 - The VM is live migrated.
 - The stimer config and count are deserialized, auto-enable is ON, the
   stimer is re-enabled.
 - The stimer expires right away, and injects an unwarranted interrupt.

Cc: stable@xxxxxxxxxxxxxxx
Fixes: 1f4b34f825e8 ("kvm/x86: Hyper-V SynIC timers")
Signed-off-by: Nicolas Saenz Julienne <nsaenz@xxxxxxxxxx>
Reviewed-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20231017155101.40677-1-nsaenz@xxxxxxxxxx
Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 arch/x86/kvm/hyperv.c |   10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

--- a/arch/x86/kvm/hyperv.c
+++ b/arch/x86/kvm/hyperv.c
@@ -701,10 +701,12 @@ static int stimer_set_count(struct kvm_v
 
 	stimer_cleanup(stimer);
 	stimer->count = count;
-	if (stimer->count == 0)
-		stimer->config.enable = 0;
-	else if (stimer->config.auto_enable)
-		stimer->config.enable = 1;
+	if (!host) {
+		if (stimer->count == 0)
+			stimer->config.enable = 0;
+		else if (stimer->config.auto_enable)
+			stimer->config.enable = 1;
+	}
 
 	if (stimer->config.enable)
 		stimer_mark_pending(stimer, false);






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