selftests/mm: fix hugepages cleanup too early

JIRA: https://issues.redhat.com/browse/RHEL-130531
Conflicts:
  - Missing tests: migration, mkdirty, mdwe, page_frag and rmap. Missing
    of the rmap line makes the last chunk of the patch failed to apply,
    manually fixed it.

commit 6e296bc
Author: Chunyu Hu <chuhu@redhat.com>
Date:   Fri Sep 12 09:37:09 2025 +0800

    selftests/mm: fix hugepages cleanup too early

    Patch series "Fix va_high_addr_switch.sh test failure", v3.

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

    Patch 1 fixes the hugepage setup issue that nr_hugepages is reset too
    early in run_vmtests.sh and break the later va_high_addr_switch testing.

    Patch 2 adds hugepage setup in va_high_addr_switch test, so that it can
    still work if vm_runtests.sh changes the hugepage setup someday.

    Patch 3 fixes the test failure caused by the hint addr align method change
    in hugetlb_get_unmapped_area().

    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/20250912013711.3002969-1-chuhu@redhat.com
    Link: https://lkml.kernel.org/r/20250912013711.3002969-2-chuhu@redhat.com
    Signed-off-by: Chunyu Hu <chuhu@redhat.com>
    Acked-by: David Hildenbrand <david@redhat.com>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Signed-off-by: Chunyu Hu <chuhu@redhat.com>

Author: Chunyu-Hu

tools/testing/selftests/mm/run_vmtests.sh

@@ -160,13 +160,13 @@ fi
 
 # set proper nr_hugepages
 if [ -n "$freepgs" ] && [ -n "$hpgsize_KB" ]; then
-	nr_hugepgs=$(cat /proc/sys/vm/nr_hugepages)
+	orig_nr_hugepgs=$(cat /proc/sys/vm/nr_hugepages)
 	needpgs=$((needmem_KB / hpgsize_KB))
 	tries=2
 	while [ "$tries" -gt 0 ] && [ "$freepgs" -lt "$needpgs" ]; do
 		lackpgs=$((needpgs - freepgs))
 		echo 3 > /proc/sys/vm/drop_caches
-		if ! echo $((lackpgs + nr_hugepgs)) > /proc/sys/vm/nr_hugepages; then
+		if ! echo $((lackpgs + orig_nr_hugepgs)) > /proc/sys/vm/nr_hugepages; then
 			echo "Please run this test as root"
 			exit $ksft_skip
 		fi
@@ -177,6 +177,7 @@ if [ -n "$freepgs" ] && [ -n "$hpgsize_KB" ]; then
 		done < /proc/meminfo
 		tries=$((tries - 1))
 	done
+	nr_hugepgs=$(cat /proc/sys/vm/nr_hugepages)
 	if [ "$freepgs" -lt "$needpgs" ]; then
 		printf "Not enough huge pages available (%d < %d)\n" \
 		       "$freepgs" "$needpgs"
@@ -435,6 +436,10 @@ CATEGORY="migration" run_test ./migration
 
 CATEGORY="mkdirty" run_test ./mkdirty
 
+if [ "${HAVE_HUGEPAGES}" = 1 ]; then
+	echo "$orig_nr_hugepgs" > /proc/sys/vm/nr_hugepages
+fi
+
 echo "SUMMARY: PASS=${count_pass} SKIP=${count_skip} FAIL=${count_fail}" | tap_prefix
 echo "1..${count_total}" | tap_output