[PATCH] ACPI: NUMA: Process hotpluggable memblocks when !CONFIG_MEMORY_HOTPLUG

Some systems (e.g. Hyper-V guests) have all their memory marked as
hotpluggable in SRAT. acpi_numa_memory_affinity_init(), however,
ignores all such regions when !CONFIG_MEMORY_HOTPLUG and this is
unfortunate as memory affinity (NUMA) information gets lost.

'Hot Pluggable' flag in SRAT only means that "system hardware supports
hot-add and hot-remove of this memory region", it doesn't prevent
memory from being cold-plugged there.

Ignore 'Hot Pluggable' bit instead of skipping the whole memory
affinity information when !CONFIG_MEMORY_HOTPLUG.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
---
 drivers/acpi/numa/srat.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/drivers/acpi/numa/srat.c b/drivers/acpi/numa/srat.c
index b8795fc49097..6c884f3e8332 100644
--- a/drivers/acpi/numa/srat.c
+++ b/drivers/acpi/numa/srat.c

@@ -254,9 +254,8 @@ acpi_numa_memory_affinity_init(struct acpi_srat_mem_affinity *ma)
 	}
 	if ((ma->flags & ACPI_SRAT_MEM_ENABLED) == 0)
 		goto out_err;
-	hotpluggable = ma->flags & ACPI_SRAT_MEM_HOT_PLUGGABLE;
-	if (hotpluggable && !IS_ENABLED(CONFIG_MEMORY_HOTPLUG))
-		goto out_err;
+	hotpluggable = IS_ENABLED(CONFIG_MEMORY_HOTPLUG) &&
+		(ma->flags & ACPI_SRAT_MEM_HOT_PLUGGABLE);
 
 	start = ma->base_address;
 	end = start + ma->length;

-- 
2.33.1

On Thu, Dec 16, 2021 at 10:58 AM Vitaly Kuznetsov [off-list ref] wrote:

Some systems (e.g. Hyper-V guests) have all their memory marked as
hotpluggable in SRAT. acpi_numa_memory_affinity_init(), however,
ignores all such regions when !CONFIG_MEMORY_HOTPLUG and this is
unfortunate as memory affinity (NUMA) information gets lost.

'Hot Pluggable' flag in SRAT only means that "system hardware supports
hot-add and hot-remove of this memory region", it doesn't prevent
memory from being cold-plugged there.

Ignore 'Hot Pluggable' bit instead of skipping the whole memory
affinity information when !CONFIG_MEMORY_HOTPLUG.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>

Makes sense to me, so applied as 5.17 material, but CC Dan and
Jonathan in case this can be problematic for some mm-related reason.