Hi, Nikunj, On Tue, Jan 04, 2022 at 02:58:14PM +0530, Nikunj A Dadhania wrote: > With TDP MMU being the default now, access to mmu_rmaps_stat debugfs > file causes following oops: > > BUG: kernel NULL pointer dereference, address: 0000000000000000 > PGD 0 P4D 0 > Oops: 0000 [#1] PREEMPT SMP NOPTI > CPU: 7 PID: 3185 Comm: cat Not tainted 5.16.0-rc4+ #204 > RIP: 0010:pte_list_count+0x6/0x40 > Call Trace: > <TASK> > ? kvm_mmu_rmaps_stat_show+0x15e/0x320 > seq_read_iter+0x126/0x4b0 > ? aa_file_perm+0x124/0x490 > seq_read+0xf5/0x140 > full_proxy_read+0x5c/0x80 > vfs_read+0x9f/0x1a0 > ksys_read+0x67/0xe0 > __x64_sys_read+0x19/0x20 > do_syscall_64+0x3b/0xc0 > entry_SYSCALL_64_after_hwframe+0x44/0xae > RIP: 0033:0x7fca6fc13912 > > Create mmu_rmaps_stat debugfs file only when rmaps are created. > > Reported-by: Vasant Hegde <vasant.hegde@xxxxxxx> > Tested-by: Vasant Hegde <vasant.hegde@xxxxxxx> > Signed-off-by: Nikunj A Dadhania <nikunj@xxxxxxx> Shall we put the check into kvm_mmu_rmaps_stat_show()? As iiuc the rmap can be allocated dynamically (shadow_root_allocated changing from 0->1). Thanks, -- Peter Xu
