On Tue, Mar 12, 2024 at 4:34 PM syzbot <syzbot+900d58a45dcaab9e4821@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote: > > ------------[ cut here ]------------ > WARNING: CPU: 1 PID: 5165 at arch/x86/kvm/mmu/tdp_mmu.c:1526 clear_dirty_gfn_range+0x3d6/0x540 arch/x86/kvm/mmu/tdp_mmu.c:1526 > Modules linked in: > CPU: 1 PID: 5165 Comm: syz-executor417 Not tainted 6.8.0-syzkaller-01185-g855684c7d938 #0 > Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014 > RIP: 0010:clear_dirty_gfn_range+0x3d6/0x540 arch/x86/kvm/mmu/tdp_mmu.c:1526 > Call Trace: > <TASK> > kvm_tdp_mmu_clear_dirty_slot+0x24f/0x2e0 arch/x86/kvm/mmu/tdp_mmu.c:1557 > kvm_mmu_slot_leaf_clear_dirty+0x38b/0x490 arch/x86/kvm/mmu/mmu.c:6783 > kvm_mmu_slot_apply_flags arch/x86/kvm/x86.c:12962 [inline] > kvm_arch_commit_memory_region+0x299/0x490 arch/x86/kvm/x86.c:13031 > kvm_commit_memory_region arch/x86/kvm/../../../virt/kvm/kvm_main.c:1751 [inline] > kvm_set_memslot+0x4d3/0x13e0 arch/x86/kvm/../../../virt/kvm/kvm_main.c:1994 > __kvm_set_memory_region arch/x86/kvm/../../../virt/kvm/kvm_main.c:2129 [inline] > __kvm_set_memory_region+0xdbc/0x1520 arch/x86/kvm/../../../virt/kvm/kvm_main.c:2020 > kvm_set_memory_region arch/x86/kvm/../../../virt/kvm/kvm_main.c:2150 [inline] > kvm_vm_ioctl_set_memory_region arch/x86/kvm/../../../virt/kvm/kvm_main.c:2162 [inline] > kvm_vm_ioctl+0x151c/0x3e20 arch/x86/kvm/../../../virt/kvm/kvm_main.c:5152 The reproducer uses nested virtualization to launch an L2 with EPT disabled. This creates a TDP MMU root with role.guest_mode=1, which triggers the WARN_ON() in kvm_tdp_mmu_clear_dirty_slot() because kvm_mmu_page_ad_need_write_protect() returns false whenever PML is enabled and the shadow page role.guest_mode=1. If I'm reading prepare_vmcs02_constant_state() correctly, we always disable PML when running in L2. So when enable_pml=1 and L2 runs with EPT disabled we are blind to dirty tracking L2 accesses.
