mm: re-architect the VM_UNPAGED logic
This replaces the (in my opinion horrible) VM_UNMAPPED logic with very
explicit support for a "remapped page range" aka VM_PFNMAP. It allows a
VM area to contain an arbitrary range of page table entries that the VM
never touches, and never considers to be normal pages.
Any user of "remap_pfn_range()" automatically gets this new
functionality, and doesn't even have to mark the pages reserved or
indeed mark them any other way. It just works. As a side effect, doing
mmap() on /dev/mem works for arbitrary ranges.
Sparc update from David in the next commit.
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
diff --git a/mm/memory.c b/mm/memory.c
index d1f46f4..b57fbc6 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -333,9 +333,9 @@
}
/*
- * This function is called to print an error when a pte in a
- * !VM_UNPAGED region is found pointing to an invalid pfn (which
- * is an error.
+ * This function is called to print an error when a bad pte
+ * is found. For example, we might have a PFN-mapped pte in
+ * a region that doesn't allow it.
*
* The calling function must still handle the error.
*/
@@ -350,19 +350,56 @@
}
/*
- * page_is_anon applies strict checks for an anonymous page belonging to
- * this vma at this address. It is used on VM_UNPAGED vmas, which are
- * usually populated with shared originals (which must not be counted),
- * but occasionally contain private COWed copies (when !VM_SHARED, or
- * perhaps via ptrace when VM_SHARED). An mmap of /dev/mem might window
- * free pages, pages from other processes, or from other parts of this:
- * it's tricky, but try not to be deceived by foreign anonymous pages.
+ * This function gets the "struct page" associated with a 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
+ * 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
+ * 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).
*/
-static inline int page_is_anon(struct page *page,
- struct vm_area_struct *vma, unsigned long addr)
+struct page *vm_normal_page(struct vm_area_struct *vma, unsigned long addr, pte_t pte)
{
- return page && PageAnon(page) && page_mapped(page) &&
- page_address_in_vma(page, vma) == addr;
+ unsigned long pfn = pte_pfn(pte);
+
+ if (vma->vm_flags & VM_PFNMAP) {
+ unsigned long off = (addr - vma->vm_start) >> PAGE_SHIFT;
+ if (pfn == vma->vm_pgoff + off)
+ return NULL;
+ }
+
+ /*
+ * Add some anal sanity checks for now. Eventually,
+ * we should just do "return pfn_to_page(pfn)", but
+ * in the meantime we check that we get a valid pfn,
+ * and that the resulting page looks ok.
+ *
+ * Remove this test eventually!
+ */
+ if (unlikely(!pfn_valid(pfn))) {
+ print_bad_pte(vma, pte, addr);
+ return NULL;
+ }
+
+ /*
+ * NOTE! We still have PageReserved() pages in the page
+ * tables.
+ *
+ * The PAGE_ZERO() pages and various VDSO mappings can
+ * cause them to exist.
+ */
+ return pfn_to_page(pfn);
}
/*
@@ -379,7 +416,6 @@
unsigned long vm_flags = vma->vm_flags;
pte_t pte = *src_pte;
struct page *page;
- unsigned long pfn;
/* pte contains position in swap or file, so copy. */
if (unlikely(!pte_present(pte))) {
@@ -397,22 +433,6 @@
goto out_set_pte;
}
- pfn = pte_pfn(pte);
- page = pfn_valid(pfn)? pfn_to_page(pfn): NULL;
-
- if (unlikely(vm_flags & VM_UNPAGED))
- if (!page_is_anon(page, vma, addr))
- goto out_set_pte;
-
- /*
- * If the pte points outside of valid memory but
- * the region is not VM_UNPAGED, we have a problem.
- */
- if (unlikely(!page)) {
- print_bad_pte(vma, pte, addr);
- goto out_set_pte; /* try to do something sane */
- }
-
/*
* If it's a COW mapping, write protect it both
* in the parent and the child
@@ -429,9 +449,13 @@
if (vm_flags & VM_SHARED)
pte = pte_mkclean(pte);
pte = pte_mkold(pte);
- get_page(page);
- page_dup_rmap(page);
- rss[!!PageAnon(page)]++;
+
+ page = vm_normal_page(vma, addr, pte);
+ if (page) {
+ get_page(page);
+ page_dup_rmap(page);
+ rss[!!PageAnon(page)]++;
+ }
out_set_pte:
set_pte_at(dst_mm, addr, dst_pte, pte);
@@ -543,7 +567,7 @@
* readonly mappings. The tradeoff is that copy_page_range is more
* efficient than faulting.
*/
- if (!(vma->vm_flags & (VM_HUGETLB|VM_NONLINEAR|VM_UNPAGED))) {
+ if (!(vma->vm_flags & (VM_HUGETLB|VM_NONLINEAR|VM_PFNMAP))) {
if (!vma->anon_vma)
return 0;
}
@@ -584,19 +608,10 @@
}
if (pte_present(ptent)) {
struct page *page;
- unsigned long pfn;
(*zap_work) -= PAGE_SIZE;
- pfn = pte_pfn(ptent);
- page = pfn_valid(pfn)? pfn_to_page(pfn): NULL;
-
- if (unlikely(vma->vm_flags & VM_UNPAGED)) {
- if (!page_is_anon(page, vma, addr))
- page = NULL;
- } else if (unlikely(!page))
- print_bad_pte(vma, ptent, addr);
-
+ page = vm_normal_page(vma, addr, ptent);
if (unlikely(details) && page) {
/*
* unmap_shared_mapping_pages() wants to
@@ -852,7 +867,7 @@
/*
* Do a quick page-table lookup for a single page.
*/
-struct page *follow_page(struct mm_struct *mm, unsigned long address,
+struct page *follow_page(struct vm_area_struct *vma, unsigned long address,
unsigned int flags)
{
pgd_t *pgd;
@@ -860,8 +875,8 @@
pmd_t *pmd;
pte_t *ptep, pte;
spinlock_t *ptl;
- unsigned long pfn;
struct page *page;
+ struct mm_struct *mm = vma->vm_mm;
page = follow_huge_addr(mm, address, flags & FOLL_WRITE);
if (!IS_ERR(page)) {
@@ -897,11 +912,10 @@
goto unlock;
if ((flags & FOLL_WRITE) && !pte_write(pte))
goto unlock;
- pfn = pte_pfn(pte);
- if (!pfn_valid(pfn))
+ page = vm_normal_page(vma, address, pte);
+ if (unlikely(!page))
goto unlock;
- page = pfn_to_page(pfn);
if (flags & FOLL_GET)
get_page(page);
if (flags & FOLL_TOUCH) {
@@ -974,8 +988,10 @@
return i ? : -EFAULT;
}
if (pages) {
- pages[i] = pte_page(*pte);
- get_page(pages[i]);
+ struct page *page = vm_normal_page(vma, start, *pte);
+ pages[i] = page;
+ if (page)
+ get_page(page);
}
pte_unmap(pte);
if (vmas)
@@ -1010,7 +1026,7 @@
foll_flags |= FOLL_WRITE;
cond_resched();
- while (!(page = follow_page(mm, start, foll_flags))) {
+ while (!(page = follow_page(vma, start, foll_flags))) {
int ret;
ret = __handle_mm_fault(mm, vma, start,
foll_flags & FOLL_WRITE);
@@ -1214,11 +1230,12 @@
* in 2.6 the LRU scan won't even find its pages, so this
* flag means no more than count its pages in reserved_vm,
* and omit it from core dump, even when VM_IO turned off.
- * VM_UNPAGED tells the core MM not to "manage" these pages
- * (e.g. refcount, mapcount, try to swap them out): in
- * particular, zap_pte_range does not try to free them.
+ * VM_PFNMAP tells the core MM that the base pages are just
+ * raw PFN mappings, and do not have a "struct page" associated
+ * with them.
*/
- vma->vm_flags |= VM_IO | VM_RESERVED | VM_UNPAGED;
+ vma->vm_flags |= VM_IO | VM_RESERVED | VM_PFNMAP;
+ vma->vm_pgoff = pfn;
BUG_ON(addr >= end);
pfn -= addr >> PAGE_SHIFT;
@@ -1273,6 +1290,26 @@
return pte;
}
+static inline void cow_user_page(struct page *dst, struct page *src, unsigned long va)
+{
+ /*
+ * If the source page was a PFN mapping, we don't have
+ * a "struct page" for it. We do a best-effort copy by
+ * just copying from the original user address. If that
+ * fails, we just zero-fill it. Live with it.
+ */
+ if (unlikely(!src)) {
+ void *kaddr = kmap_atomic(dst, KM_USER0);
+ unsigned long left = __copy_from_user_inatomic(kaddr, (void __user *)va, PAGE_SIZE);
+ if (left)
+ memset(kaddr, 0, PAGE_SIZE);
+ kunmap_atomic(kaddr, KM_USER0);
+ return;
+
+ }
+ copy_user_highpage(dst, src, va);
+}
+
/*
* This routine handles present pages, when users try to write
* to a shared page. It is done by copying the page to a new address
@@ -1296,28 +1333,13 @@
spinlock_t *ptl, pte_t orig_pte)
{
struct page *old_page, *src_page, *new_page;
- unsigned long pfn = pte_pfn(orig_pte);
pte_t entry;
int ret = VM_FAULT_MINOR;
- if (unlikely(!pfn_valid(pfn))) {
- /*
- * Page table corrupted: show pte and kill process.
- * Or it's an attempt to COW an out-of-map VM_UNPAGED
- * entry, which copy_user_highpage does not support.
- */
- print_bad_pte(vma, orig_pte, address);
- ret = VM_FAULT_OOM;
- goto unlock;
- }
- old_page = pfn_to_page(pfn);
+ old_page = vm_normal_page(vma, address, orig_pte);
src_page = old_page;
-
- if (unlikely(vma->vm_flags & VM_UNPAGED))
- if (!page_is_anon(old_page, vma, address)) {
- old_page = NULL;
- goto gotten;
- }
+ if (!old_page)
+ goto gotten;
if (PageAnon(old_page) && !TestSetPageLocked(old_page)) {
int reuse = can_share_swap_page(old_page);
@@ -1351,7 +1373,7 @@
new_page = alloc_page_vma(GFP_HIGHUSER, vma, address);
if (!new_page)
goto oom;
- copy_user_highpage(new_page, src_page, address);
+ cow_user_page(new_page, src_page, address);
}
/*
@@ -1812,16 +1834,7 @@
spinlock_t *ptl;
pte_t entry;
- /*
- * A VM_UNPAGED vma will normally be filled with present ptes
- * by remap_pfn_range, and never arrive here; but it might have
- * holes, or if !VM_DONTEXPAND, mremap might have expanded it.
- * It's weird enough handling anon pages in unpaged vmas, we do
- * not want to worry about ZERO_PAGEs too (it may or may not
- * matter if their counts wrap): just give them anon pages.
- */
-
- if (write_access || (vma->vm_flags & VM_UNPAGED)) {
+ if (write_access) {
/* Allocate our own private page. */
pte_unmap(page_table);
@@ -1896,8 +1909,6 @@
int anon = 0;
pte_unmap(page_table);
- BUG_ON(vma->vm_flags & VM_UNPAGED);
-
if (vma->vm_file) {
mapping = vma->vm_file->f_mapping;
sequence = mapping->truncate_count;
@@ -1930,7 +1941,7 @@
page = alloc_page_vma(GFP_HIGHUSER, vma, address);
if (!page)
goto oom;
- copy_user_highpage(page, new_page, address);
+ cow_user_page(page, new_page, address);
page_cache_release(new_page);
new_page = page;
anon = 1;