[PATCH v2 2/2] 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.
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>
---
v1 posted at: https://lore.kernel.org/patchwork/patch/1372409/

changes in v2:
- removed VM_PFNMAP clearing part of the patch, per Minchan and Christoph
- created prerequisite patch to replace BUG_ON with WARN_ON_ONCE, per Christoph

 drivers/dma-buf/heaps/system_heap.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/dma-buf/heaps/system_heap.c b/drivers/dma-buf/heaps/system_heap.c
index 17e0e9a68baf..4983f18cc2ce 100644
--- a/drivers/dma-buf/heaps/system_heap.c
+++ b/drivers/dma-buf/heaps/system_heap.c
@@ -203,8 +203,7 @@ static int system_heap_mmap(struct dma_buf *dmabuf, struct vm_area_struct *vma)
 	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;
-- 
2.30.0.365.g02bc693789-goog