[PATCH 07/13] mm: pagewalk: Add test_p?d callbacks

Steven Price
2019-02-15T17:03:32Z

It is useful to be able to skip parts of the page table tree even when
walking without VMAs. Add test_p?d callbacks similar to test_walk but
which are called just before a table at that level is walked. If the
callback returns non-zero then the entire table is skipped.

Signed-off-by: Steven Price <steven.price@arm.com>
---
include/linux/mm.h | 11 +++++++++++
mm/pagewalk.c | 24 ++++++++++++++++++++++++
2 files changed, 35 insertions(+)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 0418a018d7b3..0e4c9b6b554d 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1428,6 +1428,11 @@ void unmap_vmas(struct mmu_gather *tlb, struct vm_area_struct *start_vma,
* value means "do page table walk over the current vma,"
* and a negative one means "abort current page table walk
* right now." 1 means "skip the current vma."
+ * @test_pmd: similar to test_walk(), but called for every pmd.
+ * @test_pud: similar to test_walk(), but called for every pud.
+ * @test_p4d: similar to test_walk(), but called for every p4d.
+ * Returning 0 means walk this part of the page tables,
+ * returning 1 means to skip this range.
* @mm: mm_struct representing the target process of page table walk
* @vma: vma currently walked (NULL if walking outside vmas)
* @private: private data for callbacks' usage
@@ -1452,6 +1457,12 @@ struct mm_walk {
struct mm_walk *walk);
int (*test_walk)(unsigned long addr, unsigned long next,
struct mm_walk *walk);
+ int (*test_pmd)(unsigned long addr, unsigned long next,
+ pmd_t *pmd_start, struct mm_walk *walk);
+ int (*test_pud)(unsigned long addr, unsigned long next,
+ pud_t *pud_start, struct mm_walk *walk);
+ int (*test_p4d)(unsigned long addr, unsigned long next,
+ p4d_t *p4d_start, struct mm_walk *walk);
struct mm_struct *mm;
struct vm_area_struct *vma;
void *private;
diff --git a/mm/pagewalk.c b/mm/pagewalk.c
index b8038f852f06..bce7571c6563 100644
--- a/mm/pagewalk.c
+++ b/mm/pagewalk.c
@@ -32,6 +32,14 @@ static int walk_pmd_range(pud_t *pud, unsigned long addr, unsigned long end,
unsigned long next;
int err = 0;

+ if (walk->test_pmd) {
+ err = walk->test_pmd(addr, end, pmd_offset(pud, 0), walk);
+ if (err < 0)
+ return err;
+ if (err > 0)
+ return 0;
+ }
+
pmd = pmd_offset(pud, addr);
do {
again:
@@ -82,6 +90,14 @@ static int walk_pud_range(p4d_t *p4d, unsigned long addr, unsigned long end,
unsigned long next;
int err = 0;

+ if (walk->test_pud) {
+ err = walk->test_pud(addr, end, pud_offset(p4d, 0), walk);
+ if (err < 0)
+ return err;
+ if (err > 0)
+ return 0;
+ }
+
pud = pud_offset(p4d, addr);
do {
again:
@@ -128,6 +144,14 @@ static int walk_p4d_range(pgd_t *pgd, unsigned long addr, unsigned long end,
*/
int depth = (PTRS_PER_P4D == 1)?0:1;

+ if (walk->test_p4d) {
+ err = walk->test_p4d(addr, end, p4d_offset(pgd, 0), walk);
+ if (err < 0)
+ return err;
+ if (err > 0)
+ return 0;
+ }
+
p4d = p4d_offset(pgd, addr);
do {
next = p4d_addr_end(addr, end);
--
2.20.1