A misbehaving qemu created a situation where the ACPI SRAT table advertised one fewer proximity domains than intended. The NFIT table did describe all the expected proximity domains. This caused the device dax driver to assign an impossible target_node to the device, and when hotplugged as system memory, this would fail with the following signature: [ +0.001627] BUG: kernel NULL pointer dereference, address: 0000000000000088 [ +0.001331] #PF: supervisor read access in kernel mode [ +0.000975] #PF: error_code(0x0000) - not-present page [ +0.000976] PGD 80000001767d4067 P4D 80000001767d4067 PUD 10e0c4067 PMD 0 [ +0.001338] Oops: 0000 [#1] SMP PTI [ +0.000676] CPU: 4 PID: 22737 Comm: kswapd3 Tainted: G O 5.6.0-rc5 #9 [ +0.001457] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.13.0-0-gf21b5a4aeb02-prebuilt.qemu.org 04/01/2014 [ +0.001990] RIP: 0010:prepare_kswapd_sleep+0x7c/0xc0 [ +0.000780] Code: 89 df e8 87 fd ff ff 89 c2 31 c0 84 d2 74 e6 0f 1f 44 00 00 48 8b 05 fb af 7a 01 48 63 93 88 1d 01 00 48 8b 84 d0 20 0f 00 00 <48> 3b 98 88 00 00 00 75 28 f0 80 a0 80 00 00 00 fe f0 80 a3 38 20 [ +0.002877] RSP: 0018:ffffc900017a3e78 EFLAGS: 00010202 [ +0.000805] RAX: 0000000000000000 RBX: ffff8881209e0000 RCX: 0000000000000000 [ +0.001115] RDX: 0000000000000003 RSI: 0000000000000000 RDI: ffff8881209e0e80 [ +0.001098] RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000008000 [ +0.001092] R10: 0000000000000000 R11: 0000000000000003 R12: 0000000000000003 [ +0.001092] R13: 0000000000000003 R14: 0000000000000000 R15: ffffc900017a3ec8 [ +0.001091] FS: 0000000000000000(0000) GS:ffff888318c00000(0000) knlGS:0000000000000000 [ +0.001275] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ +0.000882] CR2: 0000000000000088 CR3: 0000000120b50002 CR4: 00000000001606e0 [ +0.001095] Call Trace: [ +0.000388] kswapd+0x103/0x520 [ +0.000494] ? finish_wait+0x80/0x80 [ +0.000547] ? balance_pgdat+0x5a0/0x5a0 [ +0.000607] kthread+0x120/0x140 [ +0.000508] ? kthread_create_on_node+0x60/0x60 [ +0.000706] ret_from_fork+0x3a/0x50 Add a check in the add_memory path to fail if the node to which we are adding memory is in the node_possible_map Cc: Michal Hocko <mhocko(a)kernel.org&gt; Cc: David Hildenbrand <david(a)redhat.com&gt; Cc: Dan Williams <dan.j.williams(a)intel.com&gt; Cc: Dave Hansen <dave.hansen(a)linux.intel.com&gt; Signed-off-by: Vishal Verma <vishal.l.verma(a)intel.com&gt; --- mm/memory_hotplug.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c index 0a54ffac8c68..ddd3347edd54 100644 --- a/mm/memory_hotplug.c +++ b/mm/memory_hotplug.c @@ -1005,6 +1005,11 @@ int __ref add_memory_resource(int nid, struct resource *res) if (ret) return ret; + if (!node_possible(nid)) { + WARN(1, "node %d was absent from the node_possible_map\n", nid); + return -ENXIO;

On Thu, 2020-04-16 at 19:12 +0200, David Hildenbrand wrote: > On 16.04.20 19:10, Vishal Verma wrote: >> >> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c >> index 0a54ffac8c68..ddd3347edd54 100644 >> --- a/mm/memory_hotplug.c >> +++ b/mm/memory_hotplug.c >> @@ -1005,6 +1005,11 @@ int __ref add_memory_resource(int nid, struct resource *res) >> if (ret) >> return ret; >> >> + if (!node_possible(nid)) { >> + WARN(1, "node %d was absent from the node_possible_map\n", nid); >> + return -ENXIO; > > Nit: I suggest using "-EINVAL" instead (e.g., returned via > check_hotplug_memory_range). > > Not sure if we should pr_err() instead of WARN (see e.g., > check_hotplug_memory_range) > Hm, I'm happy to make the changes, but EINVAL to me suggests there is a problem in the way this was called by the user. And in this case there really might not be much the user can change in case fo buggy firmware.

Same thing with the WARN - make the potential firmware bug much more obvious and visible.