ANDROID: mm: add a field to store names for private anonymous memoryold/dev/pixel3-mainline-WIP

Userspace processes often have multiple allocators that each do
anonymous mmaps to get memory.  When examining memory usage of
individual processes or systems as a whole, it is useful to be
able to break down the various heaps that were allocated by
each layer and examine their size, RSS, and physical memory
usage.

This patch adds a user pointer to the shared union in
vm_area_struct that points to a null terminated string inside
the user process containing a name for the vma.  vmas that
point to the same address will be merged, but vmas that
point to equivalent strings at different addresses will
not be merged.

Userspace can set the name for a region of memory by calling
prctl(PR_SET_VMA, PR_SET_VMA_ANON_NAME, start, len, (unsigned long)name);
Setting the name to NULL clears it.

The names of named anonymous vmas are shown in /proc/pid/maps
as [anon:<name>] and in /proc/pid/smaps in a new "Name" field
that is only present for named vmas.  If the userspace pointer
is no longer valid all or part of the name will be replaced
with "<fault>".

The idea to store a userspace pointer to reduce the complexity
within mm (at the expense of the complexity of reading
/proc/pid/mem) came from Dave Hansen.  This results in no
runtime overhead in the mm subsystem other than comparing
the anon_name pointers when considering vma merging.  The pointer
is stored in a union with fieds that are only used on file-backed
mappings, so it does not increase memory usage.

Includes fix from Jed Davis <jld@mozilla.com> for typo in
prctl_set_vma_anon_name, which could attempt to set the name
across two vmas at the same time due to a typo, which might
corrupt the vma list.  Fix it to use tmp instead of end to limit
the name setting to a single vma at a time.

Bug: 120441514
Change-Id: I9aa7b6b5ef536cd780599ba4e2fba8ceebe8b59f
Signed-off-by: Dmitry Shmidt <dimitrysh@google.com>
[AmitP: Fix get_user_pages_remote() call to align with upstream commit
        5b56d49fc31d ("mm: add locked parameter to get_user_pages_remote()")]
Signed-off-by: Amit Pundir <amit.pundir@linaro.org>
Signed-off-by: Matthias Maennich <maennich@google.com>
Signed-off-by: Sumit Semwal <sumit.semwal@linaro.org>

1 files changed, 24 insertions, 15 deletions

diff --git a/mm/mmap.c b/mm/mmap.c
index 6756b8bb0033..aea7adbdfd3b 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -986,7 +986,8 @@ again:
  */
 static inline int is_mergeable_vma(struct vm_area_struct *vma,
 				struct file *file, unsigned long vm_flags,
-				struct vm_userfaultfd_ctx vm_userfaultfd_ctx)
+				struct vm_userfaultfd_ctx vm_userfaultfd_ctx,
+				const char __user *anon_name)
 {
 	/*
 	 * VM_SOFTDIRTY should not prevent from VMA merging, if we
@@ -1004,6 +1005,8 @@ static inline int is_mergeable_vma(struct vm_area_struct *vma,
 		return 0;
 	if (!is_mergeable_vm_userfaultfd_ctx(vma, vm_userfaultfd_ctx))
 		return 0;
+	if (vma_get_anon_name(vma) != anon_name)
+		return 0;
 	return 1;
 }
 
@@ -1036,9 +1039,10 @@ static int
 can_vma_merge_before(struct vm_area_struct *vma, unsigned long vm_flags,
 		     struct anon_vma *anon_vma, struct file *file,
 		     pgoff_t vm_pgoff,
-		     struct vm_userfaultfd_ctx vm_userfaultfd_ctx)
+		     struct vm_userfaultfd_ctx vm_userfaultfd_ctx,
+		     const char __user *anon_name)
 {
-	if (is_mergeable_vma(vma, file, vm_flags, vm_userfaultfd_ctx) &&
+	if (is_mergeable_vma(vma, file, vm_flags, vm_userfaultfd_ctx, anon_name) &&
 	    is_mergeable_anon_vma(anon_vma, vma->anon_vma, vma)) {
 		if (vma->vm_pgoff == vm_pgoff)
 			return 1;
@@ -1057,9 +1061,10 @@ static int
 can_vma_merge_after(struct vm_area_struct *vma, unsigned long vm_flags,
 		    struct anon_vma *anon_vma, struct file *file,
 		    pgoff_t vm_pgoff,
-		    struct vm_userfaultfd_ctx vm_userfaultfd_ctx)
+		    struct vm_userfaultfd_ctx vm_userfaultfd_ctx,
+		    const char __user *anon_name)
 {
-	if (is_mergeable_vma(vma, file, vm_flags, vm_userfaultfd_ctx) &&
+	if (is_mergeable_vma(vma, file, vm_flags, vm_userfaultfd_ctx, anon_name) &&
 	    is_mergeable_anon_vma(anon_vma, vma->anon_vma, vma)) {
 		pgoff_t vm_pglen;
 		vm_pglen = vma_pages(vma);
@@ -1070,9 +1075,9 @@ can_vma_merge_after(struct vm_area_struct *vma, unsigned long vm_flags,
 }
 
 /*
- * Given a mapping request (addr,end,vm_flags,file,pgoff), figure out
- * whether that can be merged with its predecessor or its successor.
- * Or both (it neatly fills a hole).
+ * Given a mapping request (addr,end,vm_flags,file,pgoff,anon_name),
+ * figure out whether that can be merged with its predecessor or its
+ * successor.  Or both (it neatly fills a hole).
  *
  * In most cases - when called for mmap, brk or mremap - [addr,end) is
  * certain not to be mapped by the time vma_merge is called; but when
@@ -1117,7 +1122,8 @@ struct vm_area_struct *vma_merge(struct mm_struct *mm,
 			unsigned long end, unsigned long vm_flags,
 			struct anon_vma *anon_vma, struct file *file,
 			pgoff_t pgoff, struct mempolicy *policy,
-			struct vm_userfaultfd_ctx vm_userfaultfd_ctx)
+			struct vm_userfaultfd_ctx vm_userfaultfd_ctx,
+			const char __user *anon_name)
 {
 	pgoff_t pglen = (end - addr) >> PAGE_SHIFT;
 	struct vm_area_struct *area, *next;
@@ -1150,7 +1156,8 @@ struct vm_area_struct *vma_merge(struct mm_struct *mm,
 			mpol_equal(vma_policy(prev), policy) &&
 			can_vma_merge_after(prev, vm_flags,
 					    anon_vma, file, pgoff,
-					    vm_userfaultfd_ctx)) {
+					    vm_userfaultfd_ctx,
+					    anon_name)) {
 		/*
 		 * OK, it can.  Can we now merge in the successor as well?
 		 */
@@ -1159,7 +1166,8 @@ struct vm_area_struct *vma_merge(struct mm_struct *mm,
 				can_vma_merge_before(next, vm_flags,
 						     anon_vma, file,
 						     pgoff+pglen,
-						     vm_userfaultfd_ctx) &&
+						     vm_userfaultfd_ctx,
+						     anon_name) &&
 				is_mergeable_anon_vma(prev->anon_vma,
 						      next->anon_vma, NULL)) {
 							/* cases 1, 6 */
@@ -1182,7 +1190,8 @@ struct vm_area_struct *vma_merge(struct mm_struct *mm,
 			mpol_equal(policy, vma_policy(next)) &&
 			can_vma_merge_before(next, vm_flags,
 					     anon_vma, file, pgoff+pglen,
-					     vm_userfaultfd_ctx)) {
+					     vm_userfaultfd_ctx,
+					     anon_name)) {
 		if (prev && addr < prev->vm_end)	/* case 4 */
 			err = __vma_adjust(prev, prev->vm_start,
 					 addr, prev->vm_pgoff, NULL, next);
@@ -1732,7 +1741,7 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
 	 * Can we just expand an old mapping?
 	 */
 	vma = vma_merge(mm, prev, addr, addr + len, vm_flags,
-			NULL, file, pgoff, NULL, NULL_VM_UFFD_CTX);
+			NULL, file, pgoff, NULL, NULL_VM_UFFD_CTX, NULL);
 	if (vma)
 		goto out;
 
@@ -3010,7 +3019,7 @@ static int do_brk_flags(unsigned long addr, unsigned long len, unsigned long fla
 
 	/* Can we just expand an old private anonymous mapping? */
 	vma = vma_merge(mm, prev, addr, addr + len, flags,
-			NULL, NULL, pgoff, NULL, NULL_VM_UFFD_CTX);
+			NULL, NULL, pgoff, NULL, NULL_VM_UFFD_CTX, NULL);
 	if (vma)
 		goto out;
 
@@ -3208,7 +3217,7 @@ struct vm_area_struct *copy_vma(struct vm_area_struct **vmap,
 		return NULL;	/* should never get here */
 	new_vma = vma_merge(mm, prev, addr, addr + len, vma->vm_flags,
 			    vma->anon_vma, vma->vm_file, pgoff, vma_policy(vma),
-			    vma->vm_userfaultfd_ctx);
+			    vma->vm_userfaultfd_ctx, vma_get_anon_name(vma));
 	if (new_vma) {
 		/*
 		 * Source vma may have been merged into new_vma