[syzbot ci] Re: KVM: x86: Document and enforce APIC base memory hole

[syzbot ci <syzbot+cie24f8b96f7149963@syzkaller.appspotmail.com>]

syzbot ci has tested the following series

[v1] KVM: x86: Document and enforce APIC base memory hole
https://lore.kernel.org/all/20260706092021.3625908-2-twiederh@redhat.com
* [PATCH 1/4] KVM: x86: Document that KVM_CREATE_IRQCHIP must precede vcpu creation
* [PATCH 2/4] KVM: x86: Document APIC base address constraint for in-kernel irqchip
* [PATCH 3/4] KVM: x86: Reject KVM_CREATE_IRQCHIP if APIC base is already mapped
* [PATCH 4/4] KVM: x86: Reject user memory regions covering the APIC base

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

Full report is available here:
https://ci.syzbot.org/series/b02ae7eb-bae2-492f-88f2-fa1b511c93cf

***

WARNING: suspicious RCU usage in gfn_to_memslot

tree:      kvm-next
URL:       https://kernel.googlesource.com/pub/scm/virt/kvm/kvm/
base:      8cd9520d35a6c38db6567e97dd93b1f11f185dc6
arch:      amd64
compiler:  Debian clang version 22.1.6 (++20260514074242+fc4aad7b5db3-1~exp1~20260514074407.73), Debian LLD 22.1.6
config:    https://ci.syzbot.org/builds/2e25da54-5ae8-4f08-889d-30a90ffbe688/config
syz repro: https://ci.syzbot.org/findings/707c5fee-46af-42c3-9700-7fc53ef58eb2/syz_repro

=============================
WARNING: suspicious RCU usage
syzkaller #0 Not tainted
-----------------------------
./include/linux/kvm_host.h:1084 suspicious rcu_dereference_check() usage!

other info that might help us debug this:


rcu_scheduler_active = 2, debug_locks = 1
1 lock held by syz.0.17/5871:
 #0: ffff888113334b40 (&kvm->lock){+.+.}-{4:4}, at: kvm_arch_vm_ioctl+0x8d1/0x1990 arch/x86/kvm/x86.c:7320

stack backtrace:
CPU: 0 UID: 0 PID: 5871 Comm: syz.0.17 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 lib/dump_stack.c:120
 lockdep_rcu_suspicious+0x13f/0x1d0 kernel/locking/lockdep.c:6876
 __kvm_memslots include/linux/kvm_host.h:1082 [inline]
 kvm_memslots include/linux/kvm_host.h:1089 [inline]
 gfn_to_memslot+0x3df/0x420 virt/kvm/kvm_main.c:2630
 kvm_arch_vm_ioctl+0x1590/0x1990 arch/x86/kvm/x86.c:7340
 kvm_vm_ioctl+0x8f7/0xd30 virt/kvm/kvm_main.c:5381
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x174/0x580 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fd744b9ce59
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:00007fd7459b7028 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007fd744e15fa0 RCX: 00007fd744b9ce59
RDX: 0000000000000000 RSI: 000000000000ae60 RDI: 0000000000000004
RBP: 00007fd744c32e6f R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fd744e16038 R14: 00007fd744e15fa0 R15: 00007ffe5f70a5a8
 </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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