[PATCH 1/1] dma-buf: heaps: Map system heap pages as managed by linux vm

[Suren Baghdasaryan]

Currently system heap maps its buffers with VM_PFNMAP flag using
remap_pfn_range. This results in such buffers not being accounted
for in PSS calculations because vm treats this memory as having no
page structs. Without page structs there are no counters representing
how many processes are mapping a page and therefore PSS calculation
is impossible.
Historically, ION driver used to map its buffers as VM_PFNMAP areas
due to memory carveouts that did not have page structs [1]. That
is not the case anymore and it seems there was desire to move away
from remap_pfn_range [2].
Dmabuf system heap design inherits this ION behavior and maps its
pages using remap_pfn_range even though allocated pages are backed
by page structs.
Clear VM_IO and VM_PFNMAP flags when mapping memory allocated by the
system heap and replace remap_pfn_range with vm_insert_page, following
Laura's suggestion in [1]. This would allow correct PSS calculation
for dmabufs.

[1] https://driverdev-devel.linuxdriverproject.narkive.com/v0fJGpaD/using-ion-memory-for-direct-io
[2] http://driverdev.linuxdriverproject.org/pipermail/driverdev-devel/2018-October/127519.html
(sorry, could not find lore links for these discussions)

Suggested-by: Laura Abbott <labbott at kernel.org>
Signed-off-by: Suren Baghdasaryan <surenb at google.com>
---
 drivers/dma-buf/heaps/system_heap.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/dma-buf/heaps/system_heap.c b/drivers/dma-buf/heaps/system_heap.c
index 17e0e9a68baf..0e92e42b2251 100644
--- a/drivers/dma-buf/heaps/system_heap.c
+++ b/drivers/dma-buf/heaps/system_heap.c
@@ -200,11 +200,13 @@ static int system_heap_mmap(struct dma_buf *dmabuf, struct vm_area_struct *vma)
 	struct sg_page_iter piter;
 	int ret;
 
+	/* All pages are backed by a "struct page" */
+	vma->vm_flags &= ~VM_PFNMAP;
+
 	for_each_sgtable_page(table, &piter, vma->vm_pgoff) {
 		struct page *page = sg_page_iter_page(&piter);
 
-		ret = remap_pfn_range(vma, addr, page_to_pfn(page), PAGE_SIZE,
-				      vma->vm_page_prot);
+		ret = vm_insert_page(vma, addr, page);
 		if (ret)
 			return ret;
 		addr += PAGE_SIZE;
-- 
2.30.0.280.ga3ce27912f-goog