From 7a36d680658ba5a0d350f2ad275b97156b8d4333 Mon Sep 17 00:00:00 2001 From: David Woodhouse Date: Tue, 27 Feb 2024 11:49:19 +0000 Subject: [PATCH] KVM: x86/xen: fix recursive deadlock in timer injection The fast-path timer delivery introduced a recursive locking deadlock when userspace configures a timer which has already expired and is delivered immediately. The call to kvm_xen_inject_timer_irqs() can call to kvm_xen_set_evtchn() which may take kvm->arch.xen.xen_lock, which is already held in kvm_xen_vcpu_get_attr(). ============================================ WARNING: possible recursive locking detected 6.8.0-smp--5e10b4d51d77-drs #232 Tainted: G O -------------------------------------------- xen_shinfo_test/250013 is trying to acquire lock: ffff938c9930cc30 (&kvm->arch.xen.xen_lock){+.+.}-{3:3}, at: kvm_xen_set_evtchn+0x74/0x170 [kvm] but task is already holding lock: ffff938c9930cc30 (&kvm->arch.xen.xen_lock){+.+.}-{3:3}, at: kvm_xen_vcpu_get_attr+0x38/0x250 [kvm] Now that the gfn_to_pfn_cache has its own self-sufficient locking, its callers no longer need to ensure serialization, so just stop taking kvm->arch.xen.xen_lock from kvm_xen_set_evtchn(). Fixes: 77c9b9dea4fb ("KVM: x86/xen: Use fast path for Xen timer delivery") Signed-off-by: David Woodhouse Reviewed-by: Paul Durrant Link: https://lore.kernel.org/r/20240227115648.3104-6-dwmw2@infradead.org Signed-off-by: Sean Christopherson --- arch/x86/kvm/xen.c | 4 ---- 1 file changed, 4 deletions(-) diff --git a/arch/x86/kvm/xen.c b/arch/x86/kvm/xen.c index 54c4ced96b694..f65b35a05d916 100644 --- a/arch/x86/kvm/xen.c +++ b/arch/x86/kvm/xen.c @@ -1862,8 +1862,6 @@ static int kvm_xen_set_evtchn(struct kvm_xen_evtchn *xe, struct kvm *kvm) mm_borrowed = true; } - mutex_lock(&kvm->arch.xen.xen_lock); - /* * It is theoretically possible for the page to be unmapped * and the MMU notifier to invalidate the shared_info before @@ -1891,8 +1889,6 @@ static int kvm_xen_set_evtchn(struct kvm_xen_evtchn *xe, struct kvm *kvm) srcu_read_unlock(&kvm->srcu, idx); } while(!rc); - mutex_unlock(&kvm->arch.xen.xen_lock); - if (mm_borrowed) kthread_unuse_mm(kvm->mm); -- 2.30.2