From: David Woodhouse <dwmw@amazon.co.uk>
Date: Tue, 27 Feb 2024 11:49:19 +0000 (+0000)
Subject: KVM: x86/xen: fix recursive deadlock in timer injection
X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=7a36d680658ba5a0d350f2ad275b97156b8d4333;p=linux.git
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 <dwmw@amazon.co.uk>
Reviewed-by: Paul Durrant <paul@xen.org>
Link: https://lore.kernel.org/r/20240227115648.3104-6-dwmw2@infradead.org
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
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);