[PATCH v2] x86/mm: don't apply va_align to hugetlb mappings on AMD F15h

[Laurent Wandrebeck <l.wandrebeck@quelquesmots.fr>]

get_align_mask() returns huge_page_mask_align() for hugetlbfs, but
get_align_bits() adds va_align.bits regardless, so vm_unmapped_area()
returns an address off the huge page boundary and
__unmap_hugepage_range() hits BUG_ON(start & ~huge_page_mask(h)) at
teardown.

Pass the file to get_align_bits() and skip the randomisation for
hugetlbfs. Reproduced on Carrizo and FX-8370E, both hstates.

Fixes: 1317a5e7f7b1 ("arch/x86: teach arch_get_unmapped_area_vmflags to handle hugetlb mappings")
Cc: stable@vger.kernel.org # 6.13+
Suggested-by: Dave Hansen <dave.hansen@intel.com>
Signed-off-by: Laurent Wandrebeck <l.wandrebeck@quelquesmots.fr>
---
v2: put the hugetlb case in get_align_bits() instead of guarding both call
    sites, per Dave's suggestion to pass filp through. Masking rather than
    returning early cannot clear the bits: va_align.mask is an L1I way
    size, so it is a subset of huge_page_mask_align().

    Re-tested on Carrizo, both hstates.

    Link: https://lore.kernel.org/all/20260828135747.724789-1-l.wandrebeck@quelquesmots.fr/
 arch/x86/kernel/sys_x86_64.c | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kernel/sys_x86_64.c b/arch/x86/kernel/sys_x86_64.c
index 776ae6fa7f2d..4c078827f26a 100644
--- a/arch/x86/kernel/sys_x86_64.c
+++ b/arch/x86/kernel/sys_x86_64.c
@@ -50,9 +50,16 @@ static unsigned long get_align_mask(struct file *filp)
  * value before calling vm_unmapped_area() or ORed directly to the
  * address.
  */
-static unsigned long get_align_bits(void)
+static unsigned long get_align_bits(struct file *filp)
 {
-	return va_align.bits & get_align_mask(NULL);
+	/*
+	 * va_align.bits is smaller than the huge page size and will
+	 * lead to misaligned huge pages. Ignore it for huge mappings.
+	 */
+	if (is_file_hugepages(filp))
+		return 0;
+
+	return va_align.bits & get_align_mask(filp);
 }
 
 static int __init control_va_addr_alignment(char *str)
@@ -157,7 +164,7 @@ arch_get_unmapped_area(struct file *filp, unsigned long addr, unsigned long len,
 	}
 	if (filp) {
 		info.align_mask = get_align_mask(filp);
-		info.align_offset += get_align_bits();
+		info.align_offset += get_align_bits(filp);
 	}
 
 	return vm_unmapped_area(&info);
@@ -222,7 +229,7 @@ arch_get_unmapped_area_topdown(struct file *filp, unsigned long addr0,
 
 	if (filp) {
 		info.align_mask = get_align_mask(filp);
-		info.align_offset += get_align_bits();
+		info.align_offset += get_align_bits(filp);
 	}
 	addr = vm_unmapped_area(&info);
 	if (!(addr & ~PAGE_MASK))

base-commit: 93f51579e7df248780214094418f205253383cc5
-- 
2.34.1