[PATCH] KVM: x86: hyper-v: Don't auto-enable stimer during deserialization

Nicolas Saenz Julienne
2023-10-16T09:52:54Z

By not honoring the 'stimer->config.enable' state during stimer
deserialization we might introduce spurious timer interrupts. For
example through the following events:
- 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.
- We live migrate the VM.
- 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.

So let's not change the stimer's enable state if the MSR write comes
from user-space.

Fixes: 1f4b34f825e8 ("kvm/x86: Hyper-V SynIC timers")
Signed-off-by: Nicolas Saenz Julienne <nsaenz@amazon.com>
---
arch/x86/kvm/hyperv.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
index 7c2dac6824e2..9f1deb6aa131 100644
--- a/arch/x86/kvm/hyperv.c
+++ b/arch/x86/kvm/hyperv.c
@@ -729,7 +729,7 @@ static int stimer_set_count(struct kvm_vcpu_hv_stimer *stimer, u64 count,
stimer->count = count;
if (stimer->count == 0)
stimer->config.enable = 0;
- else if (stimer->config.auto_enable)
+ else if (stimer->config.auto_enable && !host)
stimer->config.enable = 1;

if (stimer->config.enable)
--
2.40.1