[moderation/CI] Re: KVM: x86/xen: Don't drop event deliveries which race memslot updates

[syzbot ci <syzbot+ci2fb68a675810f96c@syzkaller.appspotmail.com>]

syzbot ci has tested the following series

[v2] KVM: x86/xen: Don't drop event deliveries which race memslot updates
https://lore.kernel.org/all/20261014220508.518772-1-dwmw2@infradead.org
* [PATCH v2 01/11] KVM: pfncache: Return -EAGAIN for a lookup which hits an invalid memslot
* [PATCH v2 02/11] KVM: pfncache: Add a 'wait' argument to the refresh and activate functions
* [PATCH v2 03/11] KVM: x86/xen: Don't block on xen_lock within the vCPU's kvm->srcu section
* [PATCH v2 04/11] KVM: x86/xen: Wait out memslot updates in the Xen attribute ioctls
* [PATCH v2 05/11] KVM: x86/xen: Don't lose the timer event when delivery fails transiently
* [PATCH v2 06/11] KVM: x86/xen: Retry event channel delivery which races a memslot update
* [PATCH v2 07/11] KVM: x86/xen: Extract delivery of event to vCPU into a separate helper
* [PATCH v2 08/11] KVM: x86/xen: Explicitly tag "shared info" page as never being dirty tracked
* [PATCH v2 09/11] KVM: x86/xen: Don't dirty track "vCPU info" page
* [PATCH v2 10/11] KVM: x86: Request the guest TLB flush from record_steal_time()
* [PATCH v2 11/11] KVM: selftests: Add Xen evtchn vs memslot-update race test

and found the following issue:
WARNING: suspicious RCU usage in kvm_gpc_check

Full report is available here:
https://ci.syzbot.org/series/cde10220-9f8c-48fe-a62d-36d3df4d9a0b

***

WARNING: suspicious RCU usage in kvm_gpc_check

tree:      kvm-next
URL:       https://kernel.googlesource.com/pub/scm/virt/kvm/kvm/
base:      d4b7fb647204f0c81dfeae2d1a708e4d858e0c94
arch:      amd64
compiler:  Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8
config:    https://ci.syzbot.org/builds/dbdeec8a-a092-44d6-96b1-12ae99a6a0ce/config
AI triage: https://ci.syzbot.org/findings/35b5a98d-93a1-4f38-ad62-620c40c551e8/triage_trajectory

=============================
WARNING: suspicious RCU usage
syzkaller #0 Not tainted
-----------------------------
./include/linux/kvm_host.h:1094 suspicious rcu_dereference_check() usage!

other info that might help us debug this:


rcu_scheduler_active = 2, debug_locks = 1
locks held by syz.0.18064/14640: 3, last CPU#0:
 #0: ffff8881133851a8 (&vcpu->mutex){+.+.}-{4:4}, at: kvm_vcpu_ioctl+0x27f/0xfd0
 #1: ffff8880201d5d30 (&kvm->arch.xen.xen_lock){+.+.}-{4:4}, at: kvm_xen_vcpu_set_attr+0x4d/0x1250
 #2: ffff8881133861e0 (&gpc->lock){....}-{3:3}, at: xen_get_guest_pvclock+0x29/0x260

stack backtrace:
CPU: 0 UID: 0 PID: 14640 Comm: syz.0.18064 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
Call Trace:
 <TASK>
 dump_stack_lvl+0xe8/0x150
 lockdep_rcu_suspicious+0x140/0x1d0
 kvm_gpc_check+0x325/0x380
 xen_get_guest_pvclock+0x3e/0x260
 kvm_xen_start_timer+0x160/0x5f0
 kvm_xen_vcpu_set_attr+0xbb2/0x1250
 kvm_arch_vcpu_ioctl+0x1485/0x23a0
 kvm_vcpu_ioctl+0x7e3/0xfd0
 __se_sys_ioctl+0xfc/0x170
 do_syscall_64+0x166/0x520
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f3c49f9e559
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f3c4ae4a028 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f3c4a226090 RCX: 00007f3c49f9e559
RDX: 00002000000000c0 RSI: 000000004048aecb RDI: 000000000000000a
RBP: 00007f3c4a0358b0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f3c4a226128 R14: 00007f3c4a226090 R15: 00007ffed7dff5b8
 </TASK>


***

If these findings have caused you to resend the series or submit a
separate fix, please add the following tag to your commit message:
  Tested-by: syzbot@syzkaller.appspotmail.com

---
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