On Wed, Jan 05, 2022 at 09:33:37AM +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 > > Return early when rmaps are not present. > > Reported-by: Vasant Hegde <vasant.hegde@xxxxxxx> > Tested-by: Vasant Hegde <vasant.hegde@xxxxxxx> > Signed-off-by: Nikunj A Dadhania <nikunj@xxxxxxx> > --- > > v1: https://lore.kernel.org/kvm/20220104092814.11553-1-nikunj@xxxxxxx/T/#u > > Check the rmaps inside kvm_mmu_rmaps_stat_show() as the rmaps can be > allocated dynamically (Peter Xu) > > arch/x86/kvm/debugfs.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/arch/x86/kvm/debugfs.c b/arch/x86/kvm/debugfs.c > index 543a8c04025c..9240b3b7f8dd 100644 > --- a/arch/x86/kvm/debugfs.c > +++ b/arch/x86/kvm/debugfs.c > @@ -95,6 +95,9 @@ static int kvm_mmu_rmaps_stat_show(struct seq_file *m, void *v) > unsigned int *log[KVM_NR_PAGE_SIZES], *cur; > int i, j, k, l, ret; > > + if (!kvm_memslots_have_rmaps(kvm)) > + return 0; > + > ret = -ENOMEM; > memset(log, 0, sizeof(log)); > for (i = 0; i < KVM_NR_PAGE_SIZES; i++) { > -- > 2.32.0 > Reviewed-by: Peter Xu <peterx@xxxxxxxxxx> Thanks, -- Peter Xu
