When a process mmaps a file with MAP_SHARED flag, it is possible
that any other processes mmaping the same file with MAP_SHARED
flag with same permissions could share the page table entries as
well instead of creating duplicate entries. This patch introduces a
new flag MAP_SHARED_PT for mmap() which a process can use to hint
that it can share page tables with other processes using the same
mapping.
Signed-off-by: Khalid Aziz <khalid.aziz@xxxxxxxxxx>
---
include/uapi/asm-generic/mman-common.h | 1 +
mm/mmap.c | 16 ++++++++++++++++
2 files changed, 17 insertions(+)
diff --git a/include/uapi/asm-generic/mman-common.h b/include/uapi/asm-generic/mman-common.h
index 6ce1f1ceb432..4d23456b5915 100644
--- a/include/uapi/asm-generic/mman-common.h
+++ b/include/uapi/asm-generic/mman-common.h
@@ -29,6 +29,7 @@
#define MAP_HUGETLB 0x040000 /* create a huge page mapping */
#define MAP_SYNC 0x080000 /* perform synchronous page faults for the mapping */
#define MAP_FIXED_NOREPLACE 0x100000 /* MAP_FIXED which doesn't unmap underlying mapping */
+#define MAP_SHARED_PT 0x200000 /* Shared page table mappings */
#define MAP_UNINITIALIZED 0x4000000 /* For anonymous mmap, memory could be
* uninitialized */
diff --git a/mm/mmap.c b/mm/mmap.c
index d5475fbf5729..8b46d465f8d4 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1197,6 +1197,7 @@ unsigned long do_mmap(struct file *file, unsigned long addr,
struct mm_struct *mm = current->mm;
vm_flags_t vm_flags;
int pkey = 0;
+ int ptshare = 0;
validate_mm(mm);
*populate = 0;
@@ -1234,6 +1235,21 @@ unsigned long do_mmap(struct file *file, unsigned long addr,
if (mm->map_count > sysctl_max_map_count)
return -ENOMEM;
+ /*
+ * If MAP_SHARED_PT is set, MAP_SHARED or MAP_SHARED_VALIDATE must
+ * be set as well
+ */
+ if (flags & MAP_SHARED_PT) {
+#if VM_SHARED_PT
+ if (flags & (MAP_SHARED | MAP_SHARED_VALIDATE))
+ ptshare = 1;
+ else
+ return -EINVAL;
+#else
+ return -EINVAL;
+#endif
+ }
+
/* Obtain the address to map to. we verify (or select) it and ensure
* that it represents a valid section of the address space.
*/
--
2.37.2
