From: David Woodhouse <dwmw@xxxxxxxxxxxx>
In commit 5ec3289b31 ("KVM: x86/xen: Compatibility fixes for shared runstate
area") we declared it safe to obtain two gfn_to_pfn_cache locks at the same
time:
/*
* The guest's runstate_info is split across two pages and we
* need to hold and validate both GPCs simultaneously. We can
* declare a lock ordering GPC1 > GPC2 because nothing else
* takes them more than one at a time.
*/
However, we forgot to tell lockdep. Do so, by setting a subclass on the
first lock before taking the second.
Fixes: 5ec3289b31 ("KVM: x86/xen: Compatibility fixes for shared runstate area")
Suggested-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Signed-off-by: David Woodhouse <dwmw@xxxxxxxxxxxx>
---
arch/x86/kvm/xen.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/arch/x86/kvm/xen.c b/arch/x86/kvm/xen.c
index 402d9a34552c..07e61cc9881e 100644
--- a/arch/x86/kvm/xen.c
+++ b/arch/x86/kvm/xen.c
@@ -305,8 +305,10 @@ static void kvm_xen_update_runstate_guest(struct kvm_vcpu *v, bool atomic)
* The guest's runstate_info is split across two pages and we
* need to hold and validate both GPCs simultaneously. We can
* declare a lock ordering GPC1 > GPC2 because nothing else
- * takes them more than one at a time.
+ * takes them more than one at a time. Set a subclass on the
+ * gpc1 lock to make lockdep shut up about it.
*/
+ lock_set_subclass(&gpc1->lock.dep_map, 1, _THIS_IP_);
read_lock(&gpc2->lock);
if (!kvm_gpc_check(gpc2, user_len2)) {
--
2.35.3
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