selftests/mm: fix hugepages cleanup too early

selftests/mm: fix hugepages cleanup too early

Patch series "Fix va_high_addr_switch.sh test failure", v2.

These three patches fix a va_high_addr_switch.sh test failure on x86_64.

This patch (of 3):

The nr_hugepgs variable is used to keep the original nr_hugepages at the
hugepage setup step at test beginning.  After userfaultfd test, a cleaup
is executed, both /sys/kernel/mm/hugepages/hugepages-*/nr_hugepages and
/proc/sys//vm/nr_hugepages are reset to 'original' value before
userfaultfd test starts.

Issue here is the value used to restore /proc/sys/vm/nr_hugepages is
nr_hugepgs which is the initial value before the vm_runtests.sh runs, not
the value before userfaultfd test starts.  'va_high_addr_swith.sh' tests
runs after that will possibly see no hugepages available for test, and got
EINVAL when mmap(HUGETLB), making the result invalid.

And before pkey tests, nr_hugepgs is changed to be used as a temp variable
to save nr_hugepages before pkey test, and restore it after pkey tests
finish.  The original nr_hugepages value is not tracked anymore, so no way
to restore it after all tests finish.

Add a new variable orig_nr_hugepgs to save the original nr_hugepages, and
and restore it to nr_hugepages after all tests finish.  And change to use
the nr_hugepgs variable to save the /proc/sys/vm/nr_hugeages after
hugepage setup, it's also the value before userfaultfd test starts, and
the correct value to be restored after userfaultfd finishes.  The
va_high_addr_switch.sh broken will be resolved.

Link: https://lkml.kernel.org/r/20250908124740.2946005-1-chuhu@redhat.com
Link: https://lkml.kernel.org/r/20250908124740.2946005-2-chuhu@redhat.com
Signed-off-by: Chunyu Hu <chuhu@redhat.com>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>