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Subject[PATCH] x86: fix ref-counting bug in change_page_attr()
When either calling change_page_attr() with the default attributes
pages in the direct mapping have and a page's attributes already were
set to the default or when changing the attributes from one non-default
value to another, the reference counting broke, leading to either
premature restoration of a large page or missing the opportunity to do
so.

At the same time, make __PHYSICAL_MASK_SHIFT on 64-bits the value it
architecturally ought to have.

Signed-off-by: Jan Beulich <jbeulich@novell.com>
Cc: Andi Kleen <ak@suse.de>

arch/x86/mm/ioremap_64.c | 4 +-
arch/x86/mm/pageattr_32.c | 84 +++++++++++++++++++++++++++++--------------
arch/x86/mm/pageattr_64.c | 57 +++++++++++++++++++----------
include/asm-x86/page_32.h | 10 +++++
include/asm-x86/page_64.h | 2 -
include/asm-x86/pgtable_32.h | 3 +
include/asm-x86/pgtable_64.h | 4 +-
7 files changed, 114 insertions(+), 50 deletions(-)
--- linux-2.6.24-rc5/arch/x86/mm/ioremap_64.c 2007-12-12 11:28:18.000000000 +0100
+++ 2.6.24-rc5-x86-change_page_attr/arch/x86/mm/ioremap_64.c 2007-12-04 16:01:11.000000000 +0100
@@ -48,7 +48,7 @@ ioremap_change_attr(unsigned long phys_a
* Must use a address here and not struct page because the phys addr
* can be a in hole between nodes and not have an memmap entry.
*/
- err = change_page_attr_addr(vaddr,npages,__pgprot(__PAGE_KERNEL|flags));
+ err = change_page_attr_addr(vaddr,npages,MAKE_GLOBAL(__PAGE_KERNEL|flags));
if (!err)
global_flush_tlb();
}
@@ -199,7 +199,7 @@ void iounmap(volatile void __iomem *addr

/* Reset the direct mapping. Can block */
if (p->flags >> 20)
- ioremap_change_attr(p->phys_addr, p->size, 0);
+ ioremap_change_attr(p->phys_addr, get_vm_area_size(p), 0);

/* Finally remove it */
o = remove_vm_area((void *)addr);
--- linux-2.6.24-rc5/arch/x86/mm/pageattr_32.c 2007-12-12 11:28:18.000000000 +0100
+++ 2.6.24-rc5-x86-change_page_attr/arch/x86/mm/pageattr_32.c 2007-12-04 16:01:11.000000000 +0100
@@ -116,24 +116,22 @@ static void set_pmd_pte(pte_t *kpte, uns
spin_unlock_irqrestore(&pgd_lock, flags);
}

+static pgprot_t _ref_prot[KERNEL_PGD_PTRS * PTRS_PER_PMD];
+#define ref_prot(addr) _ref_prot[__pa(addr) >> PMD_SHIFT]
+
/*
* No more special protections in this 2/4MB area - revert to a
* large page again.
*/
static inline void revert_page(struct page *kpte_page, unsigned long address)
{
- pgprot_t ref_prot;
pte_t *linear;

- ref_prot =
- ((address & LARGE_PAGE_MASK) < (unsigned long)&_etext)
- ? PAGE_KERNEL_LARGE_EXEC : PAGE_KERNEL_LARGE;
-
linear = (pte_t *)
pmd_offset(pud_offset(pgd_offset_k(address), address), address);
set_pmd_pte(linear, address,
- pfn_pte((__pa(address) & LARGE_PAGE_MASK) >> PAGE_SHIFT,
- ref_prot));
+ pte_mkhuge(pfn_pte((__pa(address) & LARGE_PAGE_MASK) >> PAGE_SHIFT,
+ ref_prot(address))));
}

static inline void save_page(struct page *kpte_page)
@@ -142,12 +140,22 @@ static inline void save_page(struct page
list_add(&kpte_page->lru, &df_list);
}

+static inline int pgprot_match(pgprot_t prot1, pgprot_t prot2)
+{
+ return !((pgprot_val(prot1) ^ pgprot_val(prot2))
+#ifdef CONFIG_X86_PAE
+ & __supported_pte_mask
+#endif
+ & ~(_PAGE_ACCESSED|_PAGE_DIRTY));
+}
+
static int
__change_page_attr(struct page *page, pgprot_t prot)
{
pte_t *kpte;
unsigned long address;
struct page *kpte_page;
+ pgprot_t old_prot, ref_prot;

BUG_ON(PageHighMem(page));
address = (unsigned long)page_address(page);
@@ -159,29 +167,31 @@ __change_page_attr(struct page *page, pg
BUG_ON(PageLRU(kpte_page));
BUG_ON(PageCompound(kpte_page));

- if (pgprot_val(prot) != pgprot_val(PAGE_KERNEL)) {
+ old_prot = pte_pgprot(pte_clrhuge(*kpte));
+ ref_prot = ref_prot(address);
+ if (!pgprot_match(prot, ref_prot)) {
if (!pte_huge(*kpte)) {
set_pte_atomic(kpte, mk_pte(page, prot));
} else {
- pgprot_t ref_prot;
- struct page *split;
-
- ref_prot =
- ((address & LARGE_PAGE_MASK) < (unsigned long)&_etext)
- ? PAGE_KERNEL_EXEC : PAGE_KERNEL;
- split = split_large_page(address, prot, ref_prot);
- if (!split)
+ BUG_ON(!pgprot_match(old_prot, ref_prot));
+ kpte_page = split_large_page(address, prot, ref_prot);
+ if (!kpte_page)
return -ENOMEM;
- set_pmd_pte(kpte,address,mk_pte(split, ref_prot));
- kpte_page = split;
+ set_pmd_pte(kpte, address,
+ mk_pte(kpte_page, PAGE_KERNEL_EXEC));
+ }
+ if (!PageReserved(kpte_page)
+ && pgprot_match(old_prot, ref_prot))
+ page_private(kpte_page)++;
+ } else if (!pgprot_match(ref_prot, old_prot)) {
+ BUG_ON(pte_huge(*kpte));
+ set_pte_atomic(kpte, mk_pte(page, ref_prot));
+ if (!PageReserved(kpte_page)) {
+ BUG_ON(page_private(kpte_page) == 0);
+ page_private(kpte_page)--;
}
- page_private(kpte_page)++;
- } else if (!pte_huge(*kpte)) {
- set_pte_atomic(kpte, mk_pte(page, PAGE_KERNEL));
- BUG_ON(page_private(kpte_page) == 0);
- page_private(kpte_page)--;
} else
- BUG();
+ return 0;

/*
* If the pte was reserved, it means it was created at boot
@@ -190,8 +200,17 @@ __change_page_attr(struct page *page, pg
*/

save_page(kpte_page);
- if (!PageReserved(kpte_page)) {
- if (cpu_has_pse && (page_private(kpte_page) == 0)) {
+ if (!PageReserved(kpte_page) && cpu_has_pse) {
+ if (page_private(kpte_page) == PTRS_PER_PTE) {
+ unsigned i;
+
+ kpte = page_address(kpte_page);
+ for (i = 0; i < PTRS_PER_PTE; ++i, ++kpte)
+ if (pgprot_match(pte_pgprot(*kpte), prot))
+ page_private(kpte_page)--;
+ ref_prot(address) = prot;
+ }
+ if (page_private(kpte_page) == 0) {
paravirt_release_pt(page_to_pfn(kpte_page));
revert_page(kpte_page, address);
}
@@ -222,8 +241,21 @@ int change_page_attr(struct page *page,
int err = 0;
int i;
unsigned long flags;
+ static char first = 1;

spin_lock_irqsave(&cpa_lock, flags);
+
+ if (unlikely(first)) {
+ unsigned long addr = PAGE_OFFSET & PMD_MASK;
+
+ /* This must match is_kernel_text(). */
+ for (; addr <= (unsigned long)__init_end; addr += PMD_SIZE)
+ ref_prot(addr) = PAGE_KERNEL_EXEC;
+ for (; addr > PAGE_OFFSET; addr += PMD_SIZE)
+ ref_prot(addr) = PAGE_KERNEL;
+ first = 0;
+ }
+
for (i = 0; i < numpages; i++, page++) {
err = __change_page_attr(page, prot);
if (err)
--- linux-2.6.24-rc5/arch/x86/mm/pageattr_64.c 2007-12-12 11:28:18.000000000 +0100
+++ 2.6.24-rc5-x86-change_page_attr/arch/x86/mm/pageattr_64.c 2007-12-04 16:01:11.000000000 +0100
@@ -98,8 +98,14 @@ static inline void save_page(struct page
list_add(&fpage->lru, &deferred_pages);
}

+/* protected by init_mm.mmap_sem */
+static pgprot_t kref_prot[] = {
+ [0 ... (KERNEL_TEXT_SIZE - 1) >> PMD_SHIFT] = PAGE_KERNEL_EXEC
+};
+#define kref_prot(kaddr) kref_prot[((kaddr) - __START_KERNEL_map) >> PMD_SHIFT]
+
/*
- * No more special protections in this 2/4MB area - revert to a
+ * No more special protections in this 2MB area - revert to a
* large page again.
*/
static void revert_page(unsigned long address, pgprot_t ref_prot)
@@ -122,55 +128,68 @@ static void revert_page(unsigned long ad
set_pte((pte_t *)pmd, large_pte);
}

+static inline int pgprot_match(pgprot_t prot1, pgprot_t prot2)
+{
+ return !((pgprot_val(prot1) ^ pgprot_val(prot2))
+ & __supported_pte_mask & ~(_PAGE_ACCESSED|_PAGE_DIRTY));
+}
+
static int
__change_page_attr(unsigned long address, unsigned long pfn, pgprot_t prot,
pgprot_t ref_prot)
{
pte_t *kpte;
struct page *kpte_page;
- pgprot_t ref_prot2;
+ pgprot_t old_prot;

kpte = lookup_address(address);
if (!kpte) return 0;
- kpte_page = virt_to_page(((unsigned long)kpte) & PAGE_MASK);
+ kpte_page = virt_to_page(kpte);
BUG_ON(PageLRU(kpte_page));
BUG_ON(PageCompound(kpte_page));
- if (pgprot_val(prot) != pgprot_val(ref_prot)) {
+ old_prot = pte_pgprot(pte_clrhuge(*kpte));
+ if (!pgprot_match(prot, ref_prot)) {
if (!pte_huge(*kpte)) {
set_pte(kpte, pfn_pte(pfn, prot));
} else {
- /*
- * split_large_page will take the reference for this
- * change_page_attr on the split page.
- */
- struct page *split;
- ref_prot2 = pte_pgprot(pte_clrhuge(*kpte));
- split = split_large_page(address, prot, ref_prot2);
- if (!split)
+ BUG_ON(!pgprot_match(old_prot, ref_prot));
+ kpte_page = split_large_page(address, prot, ref_prot);
+ if (!kpte_page)
return -ENOMEM;
- pgprot_val(ref_prot2) &= ~_PAGE_NX;
- set_pte(kpte, mk_pte(split, ref_prot2));
- kpte_page = split;
+ set_pte(kpte, mk_pte(kpte_page, PAGE_KERNEL_EXEC));
}
- page_private(kpte_page)++;
- } else if (!pte_huge(*kpte)) {
+ if (pgprot_match(old_prot, ref_prot))
+ page_private(kpte_page)++;
+ } else if (!pgprot_match(ref_prot, old_prot)) {
+ BUG_ON(pte_huge(*kpte));
set_pte(kpte, pfn_pte(pfn, ref_prot));
BUG_ON(page_private(kpte_page) == 0);
page_private(kpte_page)--;
} else
- BUG();
+ return 0;

/* on x86-64 the direct mapping set at boot is not using 4k pages */
BUG_ON(PageReserved(kpte_page));

save_page(kpte_page);
+ if (page_private(kpte_page) == PTRS_PER_PTE
+ && address >= __START_KERNEL_map
+ && address < __START_KERNEL_map + KERNEL_TEXT_SIZE) {
+ unsigned i;
+
+ kpte = page_address(kpte_page);
+ for (i = 0; i < PTRS_PER_PTE; ++i, ++kpte)
+ if (pgprot_match(pte_pgprot(*kpte), prot))
+ page_private(kpte_page)--;
+ kref_prot(address) = ref_prot = prot;
+ }
if (page_private(kpte_page) == 0)
revert_page(address, ref_prot);
return 0;
}

/*
- * Change the page attributes of an page in the linear mapping.
+ * Change the page attributes of a page in the linear mapping.
*
* This should be used when a page is mapped with a different caching policy
* than write-back somewhere - some CPUs do not like it when mappings with
--- linux-2.6.24-rc5/include/asm-x86/page_32.h 2007-12-12 11:29:30.000000000 +0100
+++ 2.6.24-rc5-x86-change_page_attr/include/asm-x86/page_32.h 2007-12-04 16:01:11.000000000 +0100
@@ -6,6 +6,16 @@
#define PAGE_SIZE (1UL << PAGE_SHIFT)
#define PAGE_MASK (~(PAGE_SIZE-1))

+#ifdef CONFIG_X86_PAE
+#define __PHYSICAL_MASK_SHIFT 52
+#define __PHYSICAL_MASK ((1ULL << __PHYSICAL_MASK_SHIFT) - 1)
+#define PHYSICAL_PAGE_MASK (~(PAGE_SIZE - 1ULL) & __PHYSICAL_MASK)
+#else
+#define __PHYSICAL_MASK_SHIFT 32
+#define __PHYSICAL_MASK (~0UL)
+#define PHYSICAL_PAGE_MASK (PAGE_MASK & __PHYSICAL_MASK)
+#endif
+
#define LARGE_PAGE_MASK (~(LARGE_PAGE_SIZE-1))
#define LARGE_PAGE_SIZE (1UL << PMD_SHIFT)

--- linux-2.6.24-rc5/include/asm-x86/page_64.h 2007-12-12 11:29:30.000000000 +0100
+++ 2.6.24-rc5-x86-change_page_attr/include/asm-x86/page_64.h 2007-12-04 16:01:11.000000000 +0100
@@ -98,7 +98,7 @@ extern unsigned long phys_base;
#define PAGE_ALIGN(addr) (((addr)+PAGE_SIZE-1)&PAGE_MASK)

/* See Documentation/x86_64/mm.txt for a description of the memory map. */
-#define __PHYSICAL_MASK_SHIFT 46
+#define __PHYSICAL_MASK_SHIFT 52
#define __PHYSICAL_MASK ((_AC(1,UL) << __PHYSICAL_MASK_SHIFT) - 1)
#define __VIRTUAL_MASK_SHIFT 48
#define __VIRTUAL_MASK ((_AC(1,UL) << __VIRTUAL_MASK_SHIFT) - 1)
--- linux-2.6.24-rc5/include/asm-x86/pgtable_32.h 2007-12-12 11:29:30.000000000 +0100
+++ 2.6.24-rc5-x86-change_page_attr/include/asm-x86/pgtable_32.h 2007-12-04 16:01:11.000000000 +0100
@@ -228,11 +228,14 @@ static inline int pte_file(pte_t pte) {
static inline pte_t pte_mkclean(pte_t pte) { (pte).pte_low &= ~_PAGE_DIRTY; return pte; }
static inline pte_t pte_mkold(pte_t pte) { (pte).pte_low &= ~_PAGE_ACCESSED; return pte; }
static inline pte_t pte_wrprotect(pte_t pte) { (pte).pte_low &= ~_PAGE_RW; return pte; }
+static inline pte_t pte_clrhuge(pte_t pte) { (pte).pte_low &= ~_PAGE_PSE; return pte; }
static inline pte_t pte_mkdirty(pte_t pte) { (pte).pte_low |= _PAGE_DIRTY; return pte; }
static inline pte_t pte_mkyoung(pte_t pte) { (pte).pte_low |= _PAGE_ACCESSED; return pte; }
static inline pte_t pte_mkwrite(pte_t pte) { (pte).pte_low |= _PAGE_RW; return pte; }
static inline pte_t pte_mkhuge(pte_t pte) { (pte).pte_low |= _PAGE_PSE; return pte; }

+#define pte_pgprot(pte) (__pgprot(pte_val(pte) & ~PHYSICAL_PAGE_MASK))
+
#ifdef CONFIG_X86_PAE
# include <asm/pgtable-3level.h>
#else
--- linux-2.6.24-rc5/include/asm-x86/pgtable_64.h 2007-12-12 11:29:30.000000000 +0100
+++ 2.6.24-rc5-x86-change_page_attr/include/asm-x86/pgtable_64.h 2007-12-04 16:01:11.000000000 +0100
@@ -344,9 +344,9 @@ static inline int pmd_large(pmd_t pte) {
#define pfn_pmd(nr,prot) (__pmd(((nr) << PAGE_SHIFT) | pgprot_val(prot)))
#define pmd_pfn(x) ((pmd_val(x) & __PHYSICAL_MASK) >> PAGE_SHIFT)

-#define pte_to_pgoff(pte) ((pte_val(pte) & PHYSICAL_PAGE_MASK) >> PAGE_SHIFT)
+#define pte_to_pgoff(pte) (pte_val(pte) >> PAGE_SHIFT)
#define pgoff_to_pte(off) ((pte_t) { ((off) << PAGE_SHIFT) | _PAGE_FILE })
-#define PTE_FILE_MAX_BITS __PHYSICAL_MASK_SHIFT
+#define PTE_FILE_MAX_BITS (64 - PAGE_SHIFT)

/* PTE - Level 1 access. */




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