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 kmem driver to ensure that the target_node for the device in question is in the nodes_possible mask. Cc: Dan Williams <dan.j.williams(a)intel.com&gt; Acked-by: Dave Hansen <dave.hansen(a)linux.intel.com&gt; Signed-off-by: Vishal Verma <vishal.l.verma(a)intel.com&gt; --- drivers/dax/kmem.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/dax/kmem.c b/drivers/dax/kmem.c index 3d0a7e702c94..760c5b4e88c8 100644 --- a/drivers/dax/kmem.c +++ b/drivers/dax/kmem.c @@ -32,7 +32,7 @@ int dev_dax_kmem_probe(struct device *dev) * unavoidable performance issues. */ numa_node = dev_dax->target_node; - if (numa_node < 0) { + if (numa_node < 0 || !node_possible(numa_node)) { dev_warn(dev, "rejecting DAX region %pR with invalid node: %d\n", res, numa_node); return -EINVAL;

On Tue, Apr 14, 2020 at 4:51 AM David Hildenbrand <david(a)redhat.com&gt; wrote: > > On 11.04.20 02:09, Vishal Verma wrote: >> 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 kmem driver to ensure that the target_node for the >> device in question is in the nodes_possible mask. >> >> Cc: Dan Williams <dan.j.williams(a)intel.com&gt; >> Acked-by: Dave Hansen <dave.hansen(a)linux.intel.com&gt; >> Signed-off-by: Vishal Verma <vishal.l.verma(a)intel.com&gt; >> --- >> drivers/dax/kmem.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/drivers/dax/kmem.c b/drivers/dax/kmem.c >> index 3d0a7e702c94..760c5b4e88c8 100644 >> --- a/drivers/dax/kmem.c >> +++ b/drivers/dax/kmem.c >> @@ -32,7 +32,7 @@ int dev_dax_kmem_probe(struct device *dev) >> * unavoidable performance issues. >> */ >> numa_node = dev_dax->target_node; >> - if (numa_node < 0) { >> + if (numa_node < 0 || !node_possible(numa_node)) { >> dev_warn(dev, "rejecting DAX region %pR with invalid node: %d\n", >> res, numa_node); >> return -EINVAL; >> > > I do wonder if we should reject that from > add_memory()..->add_memory_resource() instead, where we do the > __try_online_node(). Yes, makes sense to centralize that check internal to add_memory_resource(). However, instead of a failure let's just pick the next "closest" possible node with a firmware-workaround taint-warning to let the admin know when their added memory has an awkward numa node, but otherwise let the memory come online.