mm: add remap_pfn_range_notrack

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/20210326055505.1424432-1-hch@lst.de
Link: https://lkml.kernel.org/r/20210326055505.1424432-2-hch@lst.de
Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 64be3ba..a8335ce 100644 (file)
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2732,6 +2732,8 @@ 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 f95d120..8dc6947 100644 (file)
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2260,26 +2260,17 @@ 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)))
@@ -2309,10 +2300,6 @@ 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);
@@ -2324,12 +2311,36 @@ 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);