linux-kernel - [PATCH 2/2] selftests/mm: fix va_high_addr_switch.sh failure on x86

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Message-ID: <20250827075209.2347015-3-chuhu@redhat.com>
Date: Wed, 27 Aug 2025 15:52:09 +0800
From: Chunyu Hu <chuhu@...hat.com>
To: akpm@...ux-foundation.org,
	david@...hat.com,
	shuah@...nel.org,
	linux-mm@...ck.org
Cc: linux-kselftest@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	lorenzo.stoakes@...cle.com,
	Liam.Howlett@...cle.com,
	vbabka@...e.cz,
	rppt@...nel.org,
	surenb@...gle.com,
	mhocko@...e.com,
	chuhu@...hat.com
Subject: [PATCH 2/2] selftests/mm: fix va_high_addr_switch.sh failure on x86_64

The test will fail as below on x86_64 with cpu la57 support (will skip if
no la57 support). Note, the test requries nr_hugepages to be set first.

  # running bash ./va_high_addr_switch.sh
  # -------------------------------------
  # mmap(addr_switch_hint - pagesize, pagesize): 0x7f55b60fa000 - OK
  # mmap(addr_switch_hint - pagesize, (2 * pagesize)): 0x7f55b60f9000 - OK
  # mmap(addr_switch_hint, pagesize): 0x800000000000 - OK
  # mmap(addr_switch_hint, 2 * pagesize, MAP_FIXED): 0x800000000000 - OK
  # mmap(NULL): 0x7f55b60f9000 - OK
  # mmap(low_addr): 0x40000000 - OK
  # mmap(high_addr): 0x1000000000000 - OK
  # mmap(high_addr) again: 0xffff55b6136000 - OK
  # mmap(high_addr, MAP_FIXED): 0x1000000000000 - OK
  # mmap(-1): 0xffff55b6134000 - OK
  # mmap(-1) again: 0xffff55b6132000 - OK
  # mmap(addr_switch_hint - pagesize, pagesize): 0x7f55b60fa000 - OK
  # mmap(addr_switch_hint - pagesize, 2 * pagesize): 0x7f55b60f9000 - OK
  # mmap(addr_switch_hint - pagesize/2 , 2 * pagesize): 0x7f55b60f7000 - OK
  # mmap(addr_switch_hint, pagesize): 0x800000000000 - OK
  # mmap(addr_switch_hint, 2 * pagesize, MAP_FIXED): 0x800000000000 - OK
  # mmap(NULL, MAP_HUGETLB): 0x7f55b5c00000 - OK
  # mmap(low_addr, MAP_HUGETLB): 0x40000000 - OK
  # mmap(high_addr, MAP_HUGETLB): 0x1000000000000 - OK
  # mmap(high_addr, MAP_HUGETLB) again: 0xffff55b5e00000 - OK
  # mmap(high_addr, MAP_FIXED | MAP_HUGETLB): 0x1000000000000 - OK
  # mmap(-1, MAP_HUGETLB): 0x7f55b5c00000 - OK
  # mmap(-1, MAP_HUGETLB) again: 0x7f55b5a00000 - OK
  # mmap(addr_switch_hint - pagesize, 2*hugepagesize, MAP_HUGETLB): 0x800000000000 - FAILED
  # mmap(addr_switch_hint , 2*hugepagesize, MAP_FIXED | MAP_HUGETLB): 0x800000000000 - OK
  # [FAIL]

addr_switch_hint is defined as DFEFAULT_MAP_WINDOW in the failed test (for
x86_64, DFEFAULT_MAP_WINDOW is defined as (1UL<<47) - pagesize) in 64 bit.

Before commit cc92882ee218 ("mm: drop hugetlb_get_unmapped_area{_*}
functions"), for x86_64 hugetlb_get_unmapped_area() is handled in arch code
arch/x86/mm/hugetlbpage.c and addr is checked with map_address_hint_valid()
after align with 'addr &= huge_page_mask(h)' which is a round down way, and
it will fail the check because the addr is within the DEFAULT_MAP_WINDOW but
(addr + len) is above the DFEFAULT_MAP_WINDOW. So it wil go through the
hugetlb_get_unmmaped_area_top_down() to find an area within the
DFEFAULT_MAP_WINDOW.

After commit cc92882ee218 ("mm: drop hugetlb_get_unmapped_area{_*}
functions").  The addr hint for hugetlb_get_unmmaped_area() will be rounded
up and aligned to hugepage size with ALIGN() for all arches.  And after the
align, the addr will be above the default MAP_DEFAULT_WINDOW, and the
map_addresshint_valid() check will pass because both aligned addr (addr0)
and (addr + len) are above the DEFAULT_MAP_WINDOW, and the aligned hint
address (0x800000000000) is returned as an suitable gap is found there,
in arch_get_unmapped_area_topdown().

To still cover the case that addr is within the DEFAULT_MAP_WINDOW, and
addr + len is above the DFEFAULT_MAP_WINDOW, make the addr hint one
hugepage lower, so that after the align it's still within DEFAULT_MAP_WINDOW,
and the addr + len (2 hugepages) will be above DEFAULT_MAP_WINDOW.

Fixes: cc92882ee218 ("mm: drop hugetlb_get_unmapped_area{_*} functions")
Signed-off-by: Chunyu Hu <chuhu@...hat.com>
---
 tools/testing/selftests/mm/va_high_addr_switch.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/mm/va_high_addr_switch.c b/tools/testing/selftests/mm/va_high_addr_switch.c
index 896b3f73fc53..bd96dc3b5931 100644
--- a/tools/testing/selftests/mm/va_high_addr_switch.c
+++ b/tools/testing/selftests/mm/va_high_addr_switch.c
@@ -230,10 +230,10 @@ void testcases_init(void)
 			.msg = "mmap(-1, MAP_HUGETLB) again",
 		},
 		{
-			.addr = (void *)(addr_switch_hint - pagesize),
+			.addr = (void *)(addr_switch_hint - pagesize - hugepagesize),
 			.size = 2 * hugepagesize,
 			.flags = MAP_HUGETLB | MAP_PRIVATE | MAP_ANONYMOUS,
-			.msg = "mmap(addr_switch_hint - pagesize, 2*hugepagesize, MAP_HUGETLB)",
+			.msg = "mmap(addr_switch_hint - pagesize - hugepagesize, 2*hugepagesize, MAP_HUGETLB)",
 			.low_addr_required = 1,
 			.keep_mapped = 1,
 		},
-- 
2.49.0