linux-kernel - [PATCH 5.19 0044/1157] KVM: x86/xen: Initialize Xen timer only once

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Message-Id: <20220815180441.206951782@linuxfoundation.org>
Date:   Mon, 15 Aug 2022 19:50:00 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        syzbot+e54f930ed78eb0f85281@...kaller.appspotmail.com,
        Coleman Dietsch <dietschc@....edu>,
        Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: [PATCH 5.19 0044/1157] KVM: x86/xen: Initialize Xen timer only once

From: Coleman Dietsch <dietschc@....edu>

commit af735db31285fa699384c649be72a9f32ecbb665 upstream.

Add a check for existing xen timers before initializing a new one.

Currently kvm_xen_init_timer() is called on every
KVM_XEN_VCPU_ATTR_TYPE_TIMER, which is causing the following ODEBUG
crash when vcpu->arch.xen.timer is already set.

ODEBUG: init active (active state 0)
object type: hrtimer hint: xen_timer_callbac0
RIP: 0010:debug_print_object+0x16e/0x250 lib/debugobjects.c:502
Call Trace:
__debug_object_init
debug_hrtimer_init
debug_init
hrtimer_init
kvm_xen_init_timer
kvm_xen_vcpu_set_attr
kvm_arch_vcpu_ioctl
kvm_vcpu_ioctl
vfs_ioctl

Fixes: 536395260582 ("KVM: x86/xen: handle PV timers oneshot mode")
Cc: stable@...r.kernel.org
Link: https://syzkaller.appspot.com/bug?id=8234a9dfd3aafbf092cc5a7cd9842e3ebc45fc42
Reported-by: syzbot+e54f930ed78eb0f85281@...kaller.appspotmail.com
Signed-off-by: Coleman Dietsch <dietschc@....edu>
Reviewed-by: Sean Christopherson <seanjc@...gle.com>
Message-Id: <20220808190607.323899-2-dietschc@....edu>
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 arch/x86/kvm/xen.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/arch/x86/kvm/xen.c
+++ b/arch/x86/kvm/xen.c
@@ -713,7 +713,9 @@ int kvm_xen_vcpu_set_attr(struct kvm_vcp
 				break;
 			}
 			vcpu->arch.xen.timer_virq = data->u.timer.port;
-			kvm_xen_init_timer(vcpu);
+
+			if (!vcpu->arch.xen.timer.function)
+				kvm_xen_init_timer(vcpu);
 
 			/* Restart the timer if it's set */
 			if (data->u.timer.expires_ns)