From 23e60258aeafb04e5dd813f03cb0c8ab7b01462a Mon Sep 17 00:00:00 2001 From: David Woodhouse Date: Wed, 11 Jan 2023 18:06:48 +0000 Subject: [PATCH] KVM: x86/xen: Fix lockdep warning on "recursive" gpc locking 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 Signed-off-by: David Woodhouse Message-Id: <20230111180651.14394-1-dwmw2@infradead.org> Signed-off-by: Paolo Bonzini --- 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 2e29bdc..bfa9809 100644 --- a/arch/x86/kvm/xen.c +++ b/arch/x86/kvm/xen.c @@ -304,8 +304,10 @@ 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)) { -- 2.7.4