KVM: selftests: Increase 'maxnode' for guest_memfd tests

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.

Reported-by: Yi Lai <yi1.lai@intel.com>
Closes: https://bugzilla.kernel.org/show_bug.cgi?id=221014
Closes: https://lore.kernel.org/all/bug-221014-28872@https.bugzilla.kernel.org%2F
Signed-off-by: Kai Huang <kai.huang@intel.com>
Reviewed-by: Yuan Yao <yaoyuan@linux.alibaba.com>
Link: https://patch.msgid.link/20260302205158.178058-1-kai.huang@intel.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

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;