ANDROID: mm: add a field to store names for private anonymous memory

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is no longer valid all or part of the name will be replaced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>
[sumits: updated for 5.8-rc1: change from sem locks to mmap locks]
Signed-off-by: Sumit Semwal <sumit.semwal@linaro.org>

2 files changed, 69 insertions, 4 deletions

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index dbda4499a859..5582b2d52e67 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -123,6 +123,56 @@ static void release_task_mempolicy(struct proc_maps_private *priv)
 }
 #endif
 
+static void seq_print_vma_name(struct seq_file *m, struct vm_area_struct *vma)
+{
+	const char __user *name = vma_get_anon_name(vma);
+	struct mm_struct *mm = vma->vm_mm;
+
+	unsigned long page_start_vaddr;
+	unsigned long page_offset;
+	unsigned long num_pages;
+	unsigned long max_len = NAME_MAX;
+	int i;
+
+	page_start_vaddr = (unsigned long)name & PAGE_MASK;
+	page_offset = (unsigned long)name - page_start_vaddr;
+	num_pages = DIV_ROUND_UP(page_offset + max_len, PAGE_SIZE);
+
+	seq_puts(m, "[anon:");
+
+	for (i = 0; i < num_pages; i++) {
+		int len;
+		int write_len;
+		const char *kaddr;
+		long pages_pinned;
+		struct page *page;
+
+		pages_pinned = get_user_pages_remote(current, mm,
+				page_start_vaddr, 1, 0, &page, NULL, NULL);
+		if (pages_pinned < 1) {
+			seq_puts(m, "<fault>]");
+			return;
+		}
+
+		kaddr = (const char *)kmap(page);
+		len = min(max_len, PAGE_SIZE - page_offset);
+		write_len = strnlen(kaddr + page_offset, len);
+		seq_write(m, kaddr + page_offset, write_len);
+		kunmap(page);
+		put_page(page);
+
+		/* if strnlen hit a null terminator then we're done */
+		if (write_len != len)
+			break;
+
+		max_len -= len;
+		page_offset = 0;
+		page_start_vaddr += PAGE_SIZE;
+	}
+
+	seq_putc(m, ']');
+}
+
 static void *m_start(struct seq_file *m, loff_t *ppos)
 {
 	struct proc_maps_private *priv = m->private;
@@ -319,8 +369,15 @@ show_map_vma(struct seq_file *m, struct vm_area_struct *vma)
 			goto done;
 		}
 
-		if (is_stack(vma))
+		if (is_stack(vma)) {
 			name = "[stack]";
+			goto done;
+		}
+
+		if (vma_get_anon_name(vma)) {
+			seq_pad(m, ' ');
+			seq_print_vma_name(m, vma);
+		}
 	}
 
 done:
@@ -808,6 +865,11 @@ static int show_smap(struct seq_file *m, void *v)
 	smap_gather_stats(vma, &mss);
 
 	show_map_vma(m, vma);
+	if (vma_get_anon_name(vma)) {
+		seq_puts(m, "Name:           ");
+		seq_print_vma_name(m, vma);
+		seq_putc(m, '\n');
+	}
 
 	SEQ_PUT_DEC("Size:           ", vma->vm_end - vma->vm_start);
 	SEQ_PUT_DEC(" kB\nKernelPageSize: ", vma_kernel_pagesize(vma));
diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index 52de29000c7e..d25e73b06fa0 100644
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -911,7 +911,8 @@ static int userfaultfd_release(struct inode *inode, struct file *file)
 					 new_flags, vma->anon_vma,
 					 vma->vm_file, vma->vm_pgoff,
 					 vma_policy(vma),
-					 NULL_VM_UFFD_CTX);
+					 NULL_VM_UFFD_CTX,
+					 vma_get_anon_name(vma));
 			if (prev)
 				vma = prev;
 			else
@@ -1462,7 +1463,8 @@ static int userfaultfd_register(struct userfaultfd_ctx *ctx,
 		prev = vma_merge(mm, prev, start, vma_end, new_flags,
 				 vma->anon_vma, vma->vm_file, vma->vm_pgoff,
 				 vma_policy(vma),
-				 ((struct vm_userfaultfd_ctx){ ctx }));
+				 ((struct vm_userfaultfd_ctx){ ctx }),
+				 vma_get_anon_name(vma));
 		if (prev) {
 			vma = prev;
 			goto next;
@@ -1634,7 +1636,8 @@ static int userfaultfd_unregister(struct userfaultfd_ctx *ctx,
 		prev = vma_merge(mm, prev, start, vma_end, new_flags,
 				 vma->anon_vma, vma->vm_file, vma->vm_pgoff,
 				 vma_policy(vma),
-				 NULL_VM_UFFD_CTX);
+				 NULL_VM_UFFD_CTX,
+				 vma_get_anon_name(vma));
 		if (prev) {
 			vma = prev;
 			goto next;