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Thu, 23 Apr 2026 12:20:19 -0700 (PDT) Date: Thu, 23 Apr 2026 12:20:19 -0700 X-Google-Appengine-App-Id: s~syzkaller X-Google-Appengine-App-Id-Alias: syzkaller Message-ID: <69ea70f3.a00a0220.9259.002b.GAE@google.com> Subject: [moderation/CI] Re: KVM: x86/hyperv: Fix racy usage of vcpu->arch.hyperv From: syzbot ci To: syzkaller-upstream-moderation@googlegroups.com Cc: syzbot@lists.linux.dev Content-Type: text/plain; charset="UTF-8" syzbot ci has tested the following series [v1] KVM: x86/hyperv: Fix racy usage of vcpu->arch.hyperv https://lore.kernel.org/all/20260423140833.439512-1-seanjc@google.com * [PATCH 1/5] KVM: x86/hyperv: Get target FIFO in hv_tlb_flush_enqueue(), not caller * [PATCH 2/5] KVM: x86/hyperv: Check for NULL vCPU Hyper-V object in kvm_hv_get_tlb_flush_fifo() * [PATCH 3/5] KVM: x86/hyperv: Ensure vCPU's Hyper-V object is initialized on cross-vCPU accesses * [PATCH 4/5] KVM: x86/hyperv: Assert vCPU's mutex is held in to_hv_vcpu() * [PATCH 5/5] KVM: x86/hyperv: Use {READ,WRITE}_ONCE for cross-task synic->active accesses and found the following issue: WARNING in kvm_hv_vcpu_uninit Full report is available here: https://ci.syzbot.org/series/e1f68dae-f32a-4112-a163-7a00f36d6508 *** WARNING in kvm_hv_vcpu_uninit tree: linux-next URL: https://kernel.googlesource.com/pub/scm/linux/kernel/git/next/linux-next base: 85f871f6ba46f20d7fbc0b016b4db648c33220dd arch: amd64 compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8 config: https://ci.syzbot.org/builds/4f8c36c7-e865-4f65-bb81-e22962e8a1e0/config syz repro: https://ci.syzbot.org/findings/60fac5d8-1296-4ec7-a8e3-40f561d007e9/syz_repro ------------[ cut here ]------------ debug_locks && !(lock_is_held(&(&vcpu->mutex)->dep_map) || !refcount_read(&vcpu->kvm->users_count)) WARNING: arch/x86/kvm/hyperv.h:79 at to_hv_vcpu arch/x86/kvm/hyperv.h:78 [inline], CPU#1: syz.2.19/5974 WARNING: arch/x86/kvm/hyperv.h:79 at kvm_hv_vcpu_uninit+0x163/0x1b0 arch/x86/kvm/hyperv.c:906, CPU#1: syz.2.19/5974 Modules linked in: CPU: 1 UID: 0 PID: 5974 Comm: syz.2.19 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 RIP: 0010:to_hv_vcpu arch/x86/kvm/hyperv.h:78 [inline] RIP: 0010:kvm_hv_vcpu_uninit+0x163/0x1b0 arch/x86/kvm/hyperv.c:906 Code: 48 89 df e8 0f 0f d8 00 48 c7 03 00 00 00 00 eb 05 e8 e1 8c 6d 00 5b 41 5c 41 5e 41 5f 5d e9 c4 a8 5a 0a cc e8 ce 8c 6d 00 90 <0f> 0b 90 e9 65 ff ff ff 48 c7 c1 00 12 12 90 80 e1 07 80 c1 03 38 RSP: 0018:ffffc90003e07940 EFLAGS: 00010293 RAX: ffffffff81592fe2 RBX: ffff8881b6acd380 RCX: ffff8881046e4980 RDX: 0000000000000000 RSI: 0000000000000002 RDI: 0000000000000000 RBP: 0000000000000002 R08: ffff88817696d743 R09: 1ffff1102ed2dae8 R10: dffffc0000000000 R11: ffffed102ed2dae9 R12: 0000000000000000 R13: 00000000fffffff8 R14: ffff88817696d740 R15: dffffc0000000000 FS: 00007f4cc3a9b6c0(0000) GS:ffff8882a944f000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007f4cc2c4edd5 CR3: 000000016d918000 CR4: 0000000000352ef0 Call Trace: kvm_arch_vcpu_destroy+0x1a9/0x380 arch/x86/kvm/x86.c:12963 kvm_vm_ioctl_create_vcpu+0x69a/0x930 virt/kvm/kvm_main.c:4269 kvm_vm_ioctl+0x893/0xd50 virt/kvm/kvm_main.c:5168 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+0x14d/0xf80 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f RIP: 0033:0x7f4cc2b9c819 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:00007f4cc3a9b028 EFLAGS: 00000246 ORIG_RAX: 0000000000000010 RAX: ffffffffffffffda RBX: 00007f4cc2e15fa0 RCX: 00007f4cc2b9c819 RDX: 0000000000000000 RSI: 000000000000ae41 RDI: 0000000000000004 RBP: 00007f4cc2c32c91 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000 R13: 00007f4cc2e16038 R14: 00007f4cc2e15fa0 R15: 00007ffd36efc848 *** 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 --- This report is generated by a bot. It may contain errors. syzbot ci engineers can be reached at syzkaller@googlegroups.com. To test a patch for this bug, please reply with `#syz test` (should be on a separate line). The patch should be attached to the email. Note: arguments like custom git repos and branches are not supported. The email will later be sent to: [kvm@vger.kernel.org linux-kernel@vger.kernel.org pbonzini@redhat.com seanjc@google.com vkuznets@redhat.com] If the report looks fine to you, reply with: #syz upstream If the report is a false positive, reply with #syz invalid