| Message ID | 20250317141700.3701581-7-kevin.brodsky@arm.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | Always call constructor for kernel page tables | expand |
| Context | Check | Description |
|---|---|---|
| bjorn/pre-ci_am | success | Success |
| bjorn/build-rv32-defconfig | success | build-rv32-defconfig |
| bjorn/build-rv64-clang-allmodconfig | success | build-rv64-clang-allmodconfig |
| bjorn/build-rv64-gcc-allmodconfig | success | build-rv64-gcc-allmodconfig |
| bjorn/build-rv64-nommu-k210-defconfig | success | build-rv64-nommu-k210-defconfig |
| bjorn/build-rv64-nommu-k210-virt | success | build-rv64-nommu-k210-virt |
| bjorn/checkpatch | success | checkpatch |
| bjorn/dtb-warn-rv64 | success | dtb-warn-rv64 |
| bjorn/header-inline | success | header-inline |
| bjorn/kdoc | success | kdoc |
| bjorn/module-param | success | module-param |
| bjorn/verify-fixes | success | verify-fixes |
| bjorn/verify-signedoff | success | verify-signedoff |
diff --git a/include/linux/mm.h b/include/linux/mm.h index ee31ffd7ead2..4759da9cd633 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -3125,7 +3125,7 @@ static inline spinlock_t *pmd_lock(struct mm_struct *mm, pmd_t *pmd) static inline bool pagetable_pmd_ctor(struct mm_struct *mm, struct ptdesc *ptdesc) { - if (!pmd_ptlock_init(ptdesc)) + if (mm != &init_mm && !pmd_ptlock_init(ptdesc)) return false; ptdesc_pmd_pts_init(ptdesc); __pagetable_ctor(ptdesc);
Split page table locks are not used for pgtables associated to init_mm, at any level. pte_alloc_kernel() does not call ptlock_init() as a result. There is however no separate alloc/free functions for kernel PMDs, and pmd_ptlock_init() is called unconditionally. When ALLOC_SPLIT_PTLOCKS is true (e.g. 32-bit architectures or if CONFIG_PREEMPT_RT is selected), this results in unnecessary dynamic memory allocation every time a kernel PMD is allocated. Now that pagetable_pmd_ctor() is passed the associated mm, we can easily remove this overhead by skipping pmd_ptlock_init() if the pgtable is associated to init_mm. No special-casing is needed on the dtor path, as ptlock_free() is already called unconditionally for all levels. (ptlock_free() is a no-op unless a ptlock was allocated for the given PTP.) Signed-off-by: Kevin Brodsky <kevin.brodsky@arm.com> --- include/linux/mm.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)