[5.10.y,1/2] mm: add remap_pfn_range_notrack

Commit Message

Harshvardhan Jha Nov. 5, 2024, 3:50 p.m. UTC

From: Christoph Hellwig <[e-mail]>

commit 74ffa5a3e68504dd289135b1cf0422c19ffb3f2e

Patch series "add remap_pfn_range_notrack instead of reinventing it in i915", v2.

i915 has some reason to want to avoid the track_pfn_remap overhead in
remap_pfn_range.  Add a function to the core VM to do just that rather
than reinventing the functionality poorly in the driver.

Note that the remap_io_sg path does get exercises when using Xorg on my
Thinkpad X1, so this should be considered lightly tested, I've not managed
to hit the remap_io_mapping path at all.

This patch (of 4):

Add a version of remap_pfn_range that does not call track_pfn_range.  This
will be used to fix horrible abuses of VM internals in the i915 driver.

Link: https://lkml.kernel.org/r/[e-mail]
Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Christoph Hellwig <[e-mail]>
Acked-by: Daniel Vetter <[e-mail]>
Cc: Jani Nikula <[e-mail]>
Cc: Joonas Lahtinen <[e-mail]>
Cc: Rodrigo Vivi <[e-mail]>
Cc: Chris Wilson <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>
(cherry picked from commit 74ffa5a3e68504dd289135b1cf0422c19ffb3f2e)
Signed-off-by: Harshvardhan Jha <[e-mail]>
---
 include/linux/mm.h |  2 ++
 mm/memory.c        | 51 ++++++++++++++++++++++++++++------------------
 2 files changed, 33 insertions(+), 20 deletions(-)

Patch

diff --git a/include/linux/mm.h b/include/linux/mm.h
index b8b677f47a8da..94e630862d58c 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2749,6 +2749,8 @@  unsigned long change_prot_numa(struct vm_area_struct *vma,
 struct vm_area_struct *find_extend_vma(struct mm_struct *, unsigned long addr);
 int remap_pfn_range(struct vm_area_struct *, unsigned long addr,
 			unsigned long pfn, unsigned long size, pgprot_t);
+int remap_pfn_range_notrack(struct vm_area_struct *vma, unsigned long addr,
+		unsigned long pfn, unsigned long size, pgprot_t prot);
 int vm_insert_page(struct vm_area_struct *, unsigned long addr, struct page *);
 int vm_insert_pages(struct vm_area_struct *vma, unsigned long addr,
 			struct page **pages, unsigned long *num);
diff --git a/mm/memory.c b/mm/memory.c
index 2183003687cec..40a6cc6df9003 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2290,26 +2290,17 @@  static inline int remap_p4d_range(struct mm_struct *mm, pgd_t *pgd,
 	return 0;
 }
 
-/**
- * remap_pfn_range - remap kernel memory to userspace
- * @vma: user vma to map to
- * @addr: target page aligned user address to start at
- * @pfn: page frame number of kernel physical memory address
- * @size: size of mapping area
- * @prot: page protection flags for this mapping
- *
- * Note: this is only safe if the mm semaphore is held when called.
- *
- * Return: %0 on success, negative error code otherwise.
+/*
+ * Variant of remap_pfn_range that does not call track_pfn_remap.  The caller
+ * must have pre-validated the caching bits of the pgprot_t.
  */
-int remap_pfn_range(struct vm_area_struct *vma, unsigned long addr,
-		    unsigned long pfn, unsigned long size, pgprot_t prot)
+int remap_pfn_range_notrack(struct vm_area_struct *vma, unsigned long addr,
+		unsigned long pfn, unsigned long size, pgprot_t prot)
 {
 	pgd_t *pgd;
 	unsigned long next;
 	unsigned long end = addr + PAGE_ALIGN(size);
 	struct mm_struct *mm = vma->vm_mm;
-	unsigned long remap_pfn = pfn;
 	int err;
 
 	if (WARN_ON_ONCE(!PAGE_ALIGNED(addr)))
@@ -2339,10 +2330,6 @@  int remap_pfn_range(struct vm_area_struct *vma, unsigned long addr,
 		vma->vm_pgoff = pfn;
 	}
 
-	err = track_pfn_remap(vma, &prot, remap_pfn, addr, PAGE_ALIGN(size));
-	if (err)
-		return -EINVAL;
-
 	vma->vm_flags |= VM_IO | VM_PFNMAP | VM_DONTEXPAND | VM_DONTDUMP;
 
 	BUG_ON(addr >= end);
@@ -2354,12 +2341,36 @@  int remap_pfn_range(struct vm_area_struct *vma, unsigned long addr,
 		err = remap_p4d_range(mm, pgd, addr, next,
 				pfn + (addr >> PAGE_SHIFT), prot);
 		if (err)
-			break;
+			return err;
 	} while (pgd++, addr = next, addr != end);
 
+	return 0;
+}
+
+/**
+ * remap_pfn_range - remap kernel memory to userspace
+ * @vma: user vma to map to
+ * @addr: target page aligned user address to start at
+ * @pfn: page frame number of kernel physical memory address
+ * @size: size of mapping area
+ * @prot: page protection flags for this mapping
+ *
+ * Note: this is only safe if the mm semaphore is held when called.
+ *
+ * Return: %0 on success, negative error code otherwise.
+ */
+int remap_pfn_range(struct vm_area_struct *vma, unsigned long addr,
+		    unsigned long pfn, unsigned long size, pgprot_t prot)
+{
+	int err;
+
+	err = track_pfn_remap(vma, &prot, pfn, addr, PAGE_ALIGN(size));
 	if (err)
-		untrack_pfn(vma, remap_pfn, PAGE_ALIGN(size));
+		return -EINVAL;
 
+	err = remap_pfn_range_notrack(vma, addr, pfn, size, prot);
+	if (err)
+		untrack_pfn(vma, pfn, PAGE_ALIGN(size));
 	return err;
 }
 EXPORT_SYMBOL(remap_pfn_range);