Hi Ard
On Sat, Aug 22, 2026 at 03:53:27PM +0200, Ard Biesheuvel wrote:
From: Ard Biesheuvel <[email protected]>
Allow permission changes on huge vmappings in cases where no splitting
is needed (i.e., the region is aligned sufficiently), or when the system
has support for splitting live mappings.
Signed-off-by: Ard Biesheuvel <[email protected]>
---
arch/arm64/mm/pageattr.c | 13 ++++++++++---
1 file changed, 10 insertions(+), 3 deletions(-)
diff --git a/arch/arm64/mm/pageattr.c b/arch/arm64/mm/pageattr.c
index bbe98ac9ad8c..20ff9cb273c1 100644
--- a/arch/arm64/mm/pageattr.c
+++ b/arch/arm64/mm/pageattr.c
@@ -169,8 +169,6 @@ static int change_memory_common(unsigned long addr, int
numpages,
* we are operating on does not result in such splitting.
*
* Let's restrict ourselves to mappings created by vmalloc (or vmap).
- * Disallow VM_ALLOW_HUGE_VMAP mappings to guarantee that only page
- * mappings are updated and splitting is never needed.
*
* So check whether the [addr, addr + size) interval is entirely
* covered by precisely one VM area that has the VM_ALLOC flag set.
@@ -179,7 +177,16 @@ static int change_memory_common(unsigned long addr, int
numpages,
if (!area ||
((unsigned long)kasan_reset_tag((void *)end) >
(unsigned long)kasan_reset_tag(area->addr) + area->size) ||
- ((area->flags & (VM_ALLOC | VM_ALLOW_HUGE_VMAP)) != VM_ALLOC))
+ !(area->flags & VM_ALLOC))
+ return -EINVAL;
+
+ /*
+ * Disallow VM_ALLOW_HUGE_VMAP mappings unless the region is PMD
+ * aligned, or splitting live huge mappings is supported.
+ */
+ if ((area->flags & VM_ALLOW_HUGE_VMAP) &&
+ ((start % PMD_SIZE) || (size % PMD_SIZE)) &&
If I understand the intention here correctly, I don't think it is valid. Even
if it is PMD-sized and PMD-aligned, it would still cause a split because
the loop below is not using page order, but performs attribute changes
page by page.
Best regards,
Adrian
