On Tue, Jul 15, 2025, syzbot wrote: > Hello, > > syzbot found the following issue on: > > HEAD commit: 155a3c003e55 Merge tag 'for-6.16/dm-fixes-2' of git://git... > git tree: upstream > console output: https://syzkaller.appspot.com/x/log.txt?x=103e858c580000 > kernel config: https://syzkaller.appspot.com/x/.config?x=8d5ef2da1e1c848 > dashboard link: https://syzkaller.appspot.com/bug?extid=bc0e18379a290e5edfe4 > compiler: gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40 > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=153188f0580000 > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=16f6198c580000 > > Downloadable assets: > disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/d900f083ada3/non_bootable_disk-155a3c00.raw.xz > vmlinux: https://storage.googleapis.com/syzbot-assets/725a320dfe66/vmlinux-155a3c00.xz > kernel image: https://storage.googleapis.com/syzbot-assets/9f06899bb6f3/bzImage-155a3c00.xz > > IMPORTANT: if you fix the issue, please add the following tag to the commit: > Reported-by: syzbot+bc0e18379a290e5edfe4@xxxxxxxxxxxxxxxxxxxxxxxxx > > ------------[ cut here ]------------ > WARNING: CPU: 0 PID: 6107 at arch/x86/kvm/../../../virt/kvm/kvm_main.c:3459 kvm_read_guest_offset_cached+0x3f5/0x4b0 virt/kvm/kvm_main.c:3459 > Modules linked in: > CPU: 0 UID: 0 PID: 6107 Comm: syz.0.16 Not tainted 6.16.0-rc6-syzkaller-00002-g155a3c003e55 #0 PREEMPT(full) > Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014 > RIP: 0010:kvm_read_guest_offset_cached+0x3f5/0x4b0 virt/kvm/kvm_main.c:3459 > Code: 0f 01 e8 3e 6c 61 00 e9 9b fc ff ff e8 14 25 85 00 48 8b 3c 24 31 d2 48 89 ee e8 16 bf fa 00 e9 2e fe ff ff e8 fc 24 85 00 90 <0f> 0b 90 bb ea ff ff ff e9 4d fe ff ff e8 e9 24 85 00 48 8b 74 24 > RSP: 0018:ffffc9000349f960 EFLAGS: 00010293 > RAX: 0000000000000000 RBX: ffff888050329898 RCX: ffffffff8136ca66 > RDX: ffff88803cfa8000 RSI: ffffffff8136cd84 RDI: 0000000000000006 > RBP: 0000000000000004 R08: 0000000000000006 R09: 0000000000000008 > R10: 0000000000000000 R11: 0000000000000001 R12: 0000000000000004 > R13: ffffc90003921000 R14: 0000000000000000 R15: ffffc900039215a0 > FS: 000055558378f500(0000) GS:ffff8880d6713000(0000) knlGS:0000000000000000 > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > CR2: 0000000000000000 CR3: 0000000025de6000 CR4: 0000000000352ef0 > Call Trace: > <TASK> > apf_pageready_slot_free arch/x86/kvm/x86.c:13452 [inline] kvm_pv_enable_async_pf() sets vcpu->arch.apf.msr_en_val even if the gpa is bad, which leaves the cache in an empty state. Something like so over a few patches fixes the problem: --- arch/x86/kvm/x86.c | 32 ++++++++++++++++++-------------- 1 file changed, 18 insertions(+), 14 deletions(-) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index a1c49bc681c4..0fbbf297b3c8 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -3547,11 +3547,16 @@ static int set_msr_mce(struct kvm_vcpu *vcpu, struct msr_data *msr_info) return 0; } -static inline bool kvm_pv_async_pf_enabled(struct kvm_vcpu *vcpu) +static bool __kvm_pv_async_pf_enabled(u64 msr_en_val) { u64 mask = KVM_ASYNC_PF_ENABLED | KVM_ASYNC_PF_DELIVERY_AS_INT; - return (vcpu->arch.apf.msr_en_val & mask) == mask; + return (msr_en_val & mask) == mask; +} + +static inline bool kvm_pv_async_pf_enabled(struct kvm_vcpu *vcpu) +{ + return __kvm_pv_async_pf_enabled(vcpu->arch.apf.msr_en_val); } static int kvm_pv_enable_async_pf(struct kvm_vcpu *vcpu, u64 data) @@ -3573,22 +3578,21 @@ static int kvm_pv_enable_async_pf(struct kvm_vcpu *vcpu, u64 data) if (!lapic_in_kernel(vcpu)) return data ? 1 : 0; + if (__kvm_pv_async_pf_enabled(data) && + kvm_gfn_to_hva_cache_init(vcpu->kvm, &vcpu->arch.apf.data, gpa, + sizeof(u64))) + return 1; + vcpu->arch.apf.msr_en_val = data; - - if (!kvm_pv_async_pf_enabled(vcpu)) { - kvm_clear_async_pf_completion_queue(vcpu); - kvm_async_pf_hash_reset(vcpu); - return 0; - } - - if (kvm_gfn_to_hva_cache_init(vcpu->kvm, &vcpu->arch.apf.data, gpa, - sizeof(u64))) - return 1; - vcpu->arch.apf.send_always = (data & KVM_ASYNC_PF_SEND_ALWAYS); vcpu->arch.apf.delivery_as_pf_vmexit = data & KVM_ASYNC_PF_DELIVERY_AS_PF_VMEXIT; - kvm_async_pf_wakeup_all(vcpu); + if (kvm_pv_async_pf_enabled(vcpu)) { + kvm_clear_async_pf_completion_queue(vcpu); + kvm_async_pf_hash_reset(vcpu); + } else { + kvm_async_pf_wakeup_all(vcpu); + } return 0; } base-commit: 2a046f6a4ecce47ada50dba529ec726dd0d34351 --
