On 19.05.25 11:08, Ryan Roberts wrote:
On 18/05/2025 10:54, Dev Jain wrote:
Commit 9c006972c3fe removes the pxd_present() checks because the caller
nit: please use the standard format for describing commits: Commit 9c006972c3fe ("arm64: mmu: drop pXd_present() checks from pXd_free_pYd_table()")
checks pxd_present(). But, in case of vmap_try_huge_pud(), the caller only checks pud_present(); pud_free_pmd_page() recurses on each pmd through pmd_free_pte_page(), wherein the pmd may be none. Thus it is possible to hit a warning in the latter, since pmd_none => !pmd_table(). Thus, add a pmd_present() check in pud_free_pmd_page().
This problem was found by code inspection.
This patch is based on 6.15-rc6.
nit: please remove this to below the "---", its not part of the commit log.
Fixes: 9c006972c3fe (arm64: mmu: drop pXd_present() checks from pXd_free_pYd_table())
nit: remove empty line; the tags should all be in a single block with no empty lines.
Cc: stable@vger.kernel.org Reported-by: Ryan Roberts ryan.roberts@arm.com Signed-off-by: Dev Jain dev.jain@arm.com
v1->v2:
- Enforce check in caller
arch/arm64/mm/mmu.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c index ea6695d53fb9..5b1f4cd238ca 100644 --- a/arch/arm64/mm/mmu.c +++ b/arch/arm64/mm/mmu.c @@ -1286,7 +1286,8 @@ int pud_free_pmd_page(pud_t *pudp, unsigned long addr) next = addr; end = addr + PUD_SIZE; do {
pmd_free_pte_page(pmdp, next);
if (pmd_present(*pmdp))pmd_free_pte_page() is using READ_ONCE() to access the *pmdp to ensure it can't be torn. I suspect we don't technically need that in these functions because there can be no race with a writer.
Yeah, if there is no proper locking in place the function would already seriously mess up (double freeing etc).
But the arm64 arch code always uses READ_ONCE() for dereferencing pgtable entries for safely. Perhaps we should be consistent here?
mm/vmalloc.c: if (pmd_present(*pmd) && !pmd_free_pte_page(pmd, addr))
:)
Acked-by: David Hildenbrand david@redhat.com