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-rw-r--r--include/linux/mm.h1
-rw-r--r--mm/memory.c79
2 files changed, 59 insertions, 21 deletions
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 526f810367d9..c657ea0bd6aa 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -107,6 +107,7 @@ extern unsigned int kobjsize(const void *objp);
#define VM_ALWAYSDUMP 0x04000000 /* Always include in core dumps */
#define VM_CAN_NONLINEAR 0x08000000 /* Has ->fault & does nonlinear pages */
+#define VM_MIXEDMAP 0x10000000 /* Can contain "struct page" and pure PFN pages */
#ifndef VM_STACK_DEFAULT_FLAGS /* arch can override this */
#define VM_STACK_DEFAULT_FLAGS VM_DATA_DEFAULT_FLAGS
diff --git a/mm/memory.c b/mm/memory.c
index 46958fb97c2d..0da414c383e7 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -371,35 +371,65 @@ static inline int is_cow_mapping(unsigned int flags)
}
/*
- * This function gets the "struct page" associated with a pte.
+ * This function gets the "struct page" associated with a pte or returns
+ * NULL if no "struct page" is associated with the pte.
*
- * NOTE! Some mappings do not have "struct pages". A raw PFN mapping
- * will have each page table entry just pointing to a raw page frame
- * number, and as far as the VM layer is concerned, those do not have
- * pages associated with them - even if the PFN might point to memory
+ * A raw VM_PFNMAP mapping (ie. one that is not COWed) may not have any "struct
+ * page" backing, and even if they do, they are not refcounted. COWed pages of
+ * a VM_PFNMAP do always have a struct page, and they are normally refcounted
+ * (they are _normal_ pages).
+ *
+ * So a raw PFNMAP mapping will have each page table entry just pointing
+ * to a page frame number, and as far as the VM layer is concerned, those do
+ * not have pages associated with them - even if the PFN might point to memory
* that otherwise is perfectly fine and has a "struct page".
*
- * The way we recognize those mappings is through the rules set up
- * by "remap_pfn_range()": the vma will have the VM_PFNMAP bit set,
- * and the vm_pgoff will point to the first PFN mapped: thus every
+ * The way we recognize COWed pages within VM_PFNMAP mappings is through the
+ * rules set up by "remap_pfn_range()": the vma will have the VM_PFNMAP bit
+ * set, and the vm_pgoff will point to the first PFN mapped: thus every
* page that is a raw mapping will always honor the rule
*
* pfn_of_page == vma->vm_pgoff + ((addr - vma->vm_start) >> PAGE_SHIFT)
*
- * and if that isn't true, the page has been COW'ed (in which case it
- * _does_ have a "struct page" associated with it even if it is in a
- * VM_PFNMAP range).
+ * A call to vm_normal_page() will return NULL for such a page.
+ *
+ * If the page doesn't follow the "remap_pfn_range()" rule in a VM_PFNMAP
+ * then the page has been COW'ed. A COW'ed page _does_ have a "struct page"
+ * associated with it even if it is in a VM_PFNMAP range. Calling
+ * vm_normal_page() on such a page will therefore return the "struct page".
+ *
+ *
+ * VM_MIXEDMAP mappings can likewise contain memory with or without "struct
+ * page" backing, however the difference is that _all_ pages with a struct
+ * page (that is, those where pfn_valid is true) are refcounted and considered
+ * normal pages by the VM. The disadvantage is that pages are refcounted
+ * (which can be slower and simply not an option for some PFNMAP users). The
+ * advantage is that we don't have to follow the strict linearity rule of
+ * PFNMAP mappings in order to support COWable mappings.
+ *
+ * A call to vm_normal_page() with a VM_MIXEDMAP mapping will return the
+ * associated "struct page" or NULL for memory not backed by a "struct page".
+ *
+ *
+ * All other mappings should have a valid struct page, which will be
+ * returned by a call to vm_normal_page().
*/
struct page *vm_normal_page(struct vm_area_struct *vma, unsigned long addr, pte_t pte)
{
unsigned long pfn = pte_pfn(pte);
- if (unlikely(vma->vm_flags & VM_PFNMAP)) {
- unsigned long off = (addr - vma->vm_start) >> PAGE_SHIFT;
- if (pfn == vma->vm_pgoff + off)
- return NULL;
- if (!is_cow_mapping(vma->vm_flags))
- return NULL;
+ if (unlikely(vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP))) {
+ if (vma->vm_flags & VM_MIXEDMAP) {
+ if (!pfn_valid(pfn))
+ return NULL;
+ goto out;
+ } else {
+ unsigned long off = (addr-vma->vm_start) >> PAGE_SHIFT;
+ if (pfn == vma->vm_pgoff + off)
+ return NULL;
+ if (!is_cow_mapping(vma->vm_flags))
+ return NULL;
+ }
}
#ifdef CONFIG_DEBUG_VM
@@ -422,6 +452,7 @@ struct page *vm_normal_page(struct vm_area_struct *vma, unsigned long addr, pte_
* The PAGE_ZERO() pages and various VDSO mappings can
* cause them to exist.
*/
+out:
return pfn_to_page(pfn);
}
@@ -1232,8 +1263,11 @@ int vm_insert_pfn(struct vm_area_struct *vma, unsigned long addr,
pte_t *pte, entry;
spinlock_t *ptl;
- BUG_ON(!(vma->vm_flags & VM_PFNMAP));
- BUG_ON(is_cow_mapping(vma->vm_flags));
+ BUG_ON(!(vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP)));
+ BUG_ON((vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP)) ==
+ (VM_PFNMAP|VM_MIXEDMAP));
+ BUG_ON((vma->vm_flags & VM_PFNMAP) && is_cow_mapping(vma->vm_flags));
+ BUG_ON((vma->vm_flags & VM_MIXEDMAP) && pfn_valid(pfn));
retval = -ENOMEM;
pte = get_locked_pte(mm, addr, &ptl);
@@ -2365,10 +2399,13 @@ static noinline int do_no_pfn(struct mm_struct *mm, struct vm_area_struct *vma,
unsigned long pfn;
pte_unmap(page_table);
- BUG_ON(!(vma->vm_flags & VM_PFNMAP));
- BUG_ON(is_cow_mapping(vma->vm_flags));
+ BUG_ON(!(vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP)));
+ BUG_ON((vma->vm_flags & VM_PFNMAP) && is_cow_mapping(vma->vm_flags));
pfn = vma->vm_ops->nopfn(vma, address & PAGE_MASK);
+
+ BUG_ON((vma->vm_flags & VM_MIXEDMAP) && pfn_valid(pfn));
+
if (unlikely(pfn == NOPFN_OOM))
return VM_FAULT_OOM;
else if (unlikely(pfn == NOPFN_SIGBUS))