[PATCH 4/4] i915: fix remap_io_sg to verify the pgprot

[Christoph Hellwig <hch@xxxxxx>]

remap_io_sg claims that that the pgprot is pre-verified using an
io_mapping, but actually does not get passed an io_mapping and just
uses the pgprot in the VMA.  Remove the apply_to_page_range abuse
and just loop over remap_pfn_range for each segment.

Note: this could use io_mapping_map_user by passing an iomap to
remap_io_sg if the maintainers can verify that the pgprot in the
iomap in the only caller is indeed the desired one here.

Signed-off-by: Christoph Hellwig <hch@xxxxxx>
---
 drivers/gpu/drm/i915/i915_mm.c | 73 +++++++++++-----------------------
 1 file changed, 23 insertions(+), 50 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_mm.c b/drivers/gpu/drm/i915/i915_mm.c
index 9a777b0ff59b05..4c8cd08c672d2d 100644
--- a/drivers/gpu/drm/i915/i915_mm.c
+++ b/drivers/gpu/drm/i915/i915_mm.c
@@ -28,46 +28,10 @@
 
 #include "i915_drv.h"
 
-struct remap_pfn {
-	struct mm_struct *mm;
-	unsigned long pfn;
-	pgprot_t prot;
-
-	struct sgt_iter sgt;
-	resource_size_t iobase;
-};
+#define EXPECTED_FLAGS (VM_PFNMAP | VM_DONTEXPAND | VM_DONTDUMP)
 
 #define use_dma(io) ((io) != -1)
 
-static inline unsigned long sgt_pfn(const struct remap_pfn *r)
-{
-	if (use_dma(r->iobase))
-		return (r->sgt.dma + r->sgt.curr + r->iobase) >> PAGE_SHIFT;
-	else
-		return r->sgt.pfn + (r->sgt.curr >> PAGE_SHIFT);
-}
-
-static int remap_sg(pte_t *pte, unsigned long addr, void *data)
-{
-	struct remap_pfn *r = data;
-
-	if (GEM_WARN_ON(!r->sgt.sgp))
-		return -EINVAL;
-
-	/* Special PTE are not associated with any struct page */
-	set_pte_at(r->mm, addr, pte,
-		   pte_mkspecial(pfn_pte(sgt_pfn(r), r->prot)));
-	r->pfn++; /* track insertions in case we need to unwind later */
-
-	r->sgt.curr += PAGE_SIZE;
-	if (r->sgt.curr >= r->sgt.max)
-		r->sgt = __sgt_iter(__sg_next(r->sgt.sgp), use_dma(r->iobase));
-
-	return 0;
-}
-
-#define EXPECTED_FLAGS (VM_PFNMAP | VM_DONTEXPAND | VM_DONTDUMP)
-
 /**
  * remap_io_sg - remap an IO mapping to userspace
  * @vma: user vma to map to
@@ -82,12 +46,7 @@ int remap_io_sg(struct vm_area_struct *vma,
 		unsigned long addr, unsigned long size,
 		struct scatterlist *sgl, resource_size_t iobase)
 {
-	struct remap_pfn r = {
-		.mm = vma->vm_mm,
-		.prot = vma->vm_page_prot,
-		.sgt = __sgt_iter(sgl, use_dma(iobase)),
-		.iobase = iobase,
-	};
+	unsigned long pfn, len, remapped = 0;
 	int err;
 
 	/* We rely on prevalidation of the io-mapping to skip track_pfn(). */
@@ -96,11 +55,25 @@ int remap_io_sg(struct vm_area_struct *vma,
 	if (!use_dma(iobase))
 		flush_cache_range(vma, addr, size);
 
-	err = apply_to_page_range(r.mm, addr, size, remap_sg, &r);
-	if (unlikely(err)) {
-		zap_vma_ptes(vma, addr, r.pfn << PAGE_SHIFT);
-		return err;
-	}
-
-	return 0;
+	do {
+		if (use_dma(iobase)) {
+			if (!sg_dma_len(sgl))
+				break;
+			pfn = (sg_dma_address(sgl) + iobase) >> PAGE_SHIFT;
+			len = sg_dma_len(sgl);
+		} else {
+			pfn = page_to_pfn(sg_page(sgl));
+			len = sgl->length;
+		}
+
+		err = remap_pfn_range(vma, addr + remapped, pfn, len,
+				      vma->vm_page_prot);
+		if (err)
+			break;
+		remapped += len;
+	} while ((sgl = __sg_next(sgl)));
+
+	if (err)
+		zap_vma_ptes(vma, addr, remapped);
+	return err;
 }
-- 
2.30.1