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

[Huang, Kai]

On Mon, 2026-03-02 at 07:57 -0800, Sean Christopherson wrote:
> On Mon, Mar 02, 2026, 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 'unsigned long' (i.e.,
> > 64 on 64-bit systems) to fix this.  Note the 'nodemask' is 'unsigned
> > long', so it makes sense to set 'maxnode' to bits of 'unsigned long'
> > anyway.
> > 
> > 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.
> > 
> 
> Can you add:
> 
> 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

Oh I didn't know this was already reported.  Will do.

> 
> > Signed-off-by: Kai Huang <kai.huang@xxxxxxxxx>
> > ---
> >  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..b434612bc3ec 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 = sizeof(nodemask) * 8;
> 
> Pretty sure this can be:
> 
> 	unsigned long maxnode = BITS_PER_TYPE(nodemask)

Yeah.

Will update and send out v2 soon since this is a simple patch.