Re: [PATCH v2] KVM: selftests: Increase 'maxnode' for guest_memfd tests

[Yao Yuan]

On Tue, Mar 03, 2026 at 09:51:58AM +0800, Kai Huang wrote:
> Increase 'maxnode' when using 'get_mempolicy' syscall in guest_memfd
> mmap and NUMA policy tests to fix a failure on one Intel GNR platform.
>
> On a CXL-capable platform, the memory affinity of CXL memory regions may
> not be covered by the SRAT.  Since each CXL memory region is enumerated
> via a CFMWS table, at early boot the kernel parses all CFMWS tables to
> detect all CXL memory regions and assigns a 'faked' NUMA node for each
> of them, starting from the highest NUMA node ID enumerated via the SRAT.
>
> This increases the 'nr_node_ids'.  E.g., on the aforementioned Intel GNR
> platform which has 4 NUMA nodes and 18 CFMWS tables, it increases to 22.
>
> This results in the 'get_mempolicy' syscall failure on that platform,
> because currently 'maxnode' is hard-coded to 8 but the 'get_mempolicy'
> syscall requires the 'maxnode' to be not smaller than the 'nr_node_ids'.
>
> Increase the 'maxnode' to the number of bits of 'nodemask', which is
> 'unsigned long', to fix this.
>
> This may not cover all systems.  Perhaps a better way is to always set
> the 'nodemask' and 'maxnode' based on the actual maximum NUMA node ID on
> the system, but for now just do the simple way.

Reviewed-by: Yuan Yao <yaoyuan@xxxxxxxxxxxxxxxxx>

>
> Reported-by: Yi Lai <yi1.lai@xxxxxxxxx>
> Closes: https://bugzilla.kernel.org/show_bug.cgi?id=221014
> Closes: https://lore.kernel.org/all/bug-221014-28872@xxxxxxxxxxxxxxxxxxxxxxxxx%2F
> Signed-off-by: Kai Huang <kai.huang@xxxxxxxxx>
> ---
>
> v1 -> v2:
>  - Add 'Reported-by' and 'Closes" tags.  - Sean
>  - Use BITS_PER_TYPE().  - Sean
>  - Slightly simplify changelog to simply say "increase 'maxnode' to bits
>    of 'nodemask'" to reflect the code better.
>
> ---
>  tools/testing/selftests/kvm/guest_memfd_test.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/tools/testing/selftests/kvm/guest_memfd_test.c b/tools/testing/selftests/kvm/guest_memfd_test.c
> index 618c937f3c90..cc329b57ce2e 100644
> --- a/tools/testing/selftests/kvm/guest_memfd_test.c
> +++ b/tools/testing/selftests/kvm/guest_memfd_test.c
> @@ -80,7 +80,7 @@ static void test_mbind(int fd, size_t total_size)
>  {
>  	const unsigned long nodemask_0 = 1; /* nid: 0 */
>  	unsigned long nodemask = 0;
> -	unsigned long maxnode = 8;
> +	unsigned long maxnode = BITS_PER_TYPE(nodemask);
>  	int policy;
>  	char *mem;
>  	int ret;
>
> base-commit: a91cc48246605af9aeef1edd32232976d74d9502
> --
> 2.53.0
>