[PATCH 5.15 34/72] KVM: x86: Check for rmaps allocation

[Greg Kroah-Hartman]

From: Nikunj A Dadhania <nikunj@xxxxxxx>

commit fffb5323780786c81ba005f8b8603d4a558aad28 upstream.

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>
Reviewed-by: Peter Xu <peterx@xxxxxxxxxx>
Reviewed-by: Sean Christopherson <seanjc@xxxxxxxxxx>
Message-Id: <20220105040337.4234-1-nikunj@xxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Fixes: 3bcd0662d66f ("KVM: X86: Introduce mmu_rmaps_stat per-vm debugfs file")
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 arch/x86/kvm/debugfs.c |    3 +++
 1 file changed, 3 insertions(+)

--- a/arch/x86/kvm/debugfs.c
+++ b/arch/x86/kvm/debugfs.c
@@ -95,6 +95,9 @@ static int kvm_mmu_rmaps_stat_show(struc
 	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++) {