linux/arch/x86/mm/hugetlbpage.c
Mel Gorman 32b154c0b0 x86: ignore VM_LOCKED when determining if hugetlb-backed page tables can be shared or not
Addresses http://bugzilla.kernel.org/show_bug.cgi?id=13302

On x86 and x86-64, it is possible that page tables are shared beween
shared mappings backed by hugetlbfs.  As part of this,
page_table_shareable() checks a pair of vma->vm_flags and they must match
if they are to be shared.  All VMA flags are taken into account, including
VM_LOCKED.

The problem is that VM_LOCKED is cleared on fork().  When a process with a
shared memory segment forks() to exec() a helper, there will be shared
VMAs with different flags.  The impact is that the shared segment is
sometimes considered shareable and other times not, depending on what
process is checking.

What happens is that the segment page tables are being shared but the
count is inaccurate depending on the ordering of events.  As the page
tables are freed with put_page(), bad pmd's are found when some of the
children exit.  The hugepage counters also get corrupted and the Total and
Free count will no longer match even when all the hugepage-backed regions
are freed.  This requires a reboot of the machine to "fix".

This patch addresses the problem by comparing all flags except VM_LOCKED
when deciding if pagetables should be shared or not for hugetlbfs-backed
mapping.

Signed-off-by: Mel Gorman <mel@csn.ul.ie>
Acked-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: <stable@kernel.org>
Cc: Lee Schermerhorn <Lee.Schermerhorn@hp.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: <starlight@binnacle.cx>
Cc: Eric B Munson <ebmunson@us.ibm.com>
Cc: Adam Litke <agl@us.ibm.com>
Cc: Andy Whitcroft <apw@canonical.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-05-29 08:40:03 -07:00

449 lines
10 KiB
C

/*
* IA-32 Huge TLB Page Support for Kernel.
*
* Copyright (C) 2002, Rohit Seth <rohit.seth@intel.com>
*/
#include <linux/init.h>
#include <linux/fs.h>
#include <linux/mm.h>
#include <linux/hugetlb.h>
#include <linux/pagemap.h>
#include <linux/slab.h>
#include <linux/err.h>
#include <linux/sysctl.h>
#include <asm/mman.h>
#include <asm/tlb.h>
#include <asm/tlbflush.h>
#include <asm/pgalloc.h>
static unsigned long page_table_shareable(struct vm_area_struct *svma,
struct vm_area_struct *vma,
unsigned long addr, pgoff_t idx)
{
unsigned long saddr = ((idx - svma->vm_pgoff) << PAGE_SHIFT) +
svma->vm_start;
unsigned long sbase = saddr & PUD_MASK;
unsigned long s_end = sbase + PUD_SIZE;
/* Allow segments to share if only one is marked locked */
unsigned long vm_flags = vma->vm_flags & ~VM_LOCKED;
unsigned long svm_flags = svma->vm_flags & ~VM_LOCKED;
/*
* match the virtual addresses, permission and the alignment of the
* page table page.
*/
if (pmd_index(addr) != pmd_index(saddr) ||
vm_flags != svm_flags ||
sbase < svma->vm_start || svma->vm_end < s_end)
return 0;
return saddr;
}
static int vma_shareable(struct vm_area_struct *vma, unsigned long addr)
{
unsigned long base = addr & PUD_MASK;
unsigned long end = base + PUD_SIZE;
/*
* check on proper vm_flags and page table alignment
*/
if (vma->vm_flags & VM_MAYSHARE &&
vma->vm_start <= base && end <= vma->vm_end)
return 1;
return 0;
}
/*
* search for a shareable pmd page for hugetlb.
*/
static void huge_pmd_share(struct mm_struct *mm, unsigned long addr, pud_t *pud)
{
struct vm_area_struct *vma = find_vma(mm, addr);
struct address_space *mapping = vma->vm_file->f_mapping;
pgoff_t idx = ((addr - vma->vm_start) >> PAGE_SHIFT) +
vma->vm_pgoff;
struct prio_tree_iter iter;
struct vm_area_struct *svma;
unsigned long saddr;
pte_t *spte = NULL;
if (!vma_shareable(vma, addr))
return;
spin_lock(&mapping->i_mmap_lock);
vma_prio_tree_foreach(svma, &iter, &mapping->i_mmap, idx, idx) {
if (svma == vma)
continue;
saddr = page_table_shareable(svma, vma, addr, idx);
if (saddr) {
spte = huge_pte_offset(svma->vm_mm, saddr);
if (spte) {
get_page(virt_to_page(spte));
break;
}
}
}
if (!spte)
goto out;
spin_lock(&mm->page_table_lock);
if (pud_none(*pud))
pud_populate(mm, pud, (pmd_t *)((unsigned long)spte & PAGE_MASK));
else
put_page(virt_to_page(spte));
spin_unlock(&mm->page_table_lock);
out:
spin_unlock(&mapping->i_mmap_lock);
}
/*
* unmap huge page backed by shared pte.
*
* Hugetlb pte page is ref counted at the time of mapping. If pte is shared
* indicated by page_count > 1, unmap is achieved by clearing pud and
* decrementing the ref count. If count == 1, the pte page is not shared.
*
* called with vma->vm_mm->page_table_lock held.
*
* returns: 1 successfully unmapped a shared pte page
* 0 the underlying pte page is not shared, or it is the last user
*/
int huge_pmd_unshare(struct mm_struct *mm, unsigned long *addr, pte_t *ptep)
{
pgd_t *pgd = pgd_offset(mm, *addr);
pud_t *pud = pud_offset(pgd, *addr);
BUG_ON(page_count(virt_to_page(ptep)) == 0);
if (page_count(virt_to_page(ptep)) == 1)
return 0;
pud_clear(pud);
put_page(virt_to_page(ptep));
*addr = ALIGN(*addr, HPAGE_SIZE * PTRS_PER_PTE) - HPAGE_SIZE;
return 1;
}
pte_t *huge_pte_alloc(struct mm_struct *mm,
unsigned long addr, unsigned long sz)
{
pgd_t *pgd;
pud_t *pud;
pte_t *pte = NULL;
pgd = pgd_offset(mm, addr);
pud = pud_alloc(mm, pgd, addr);
if (pud) {
if (sz == PUD_SIZE) {
pte = (pte_t *)pud;
} else {
BUG_ON(sz != PMD_SIZE);
if (pud_none(*pud))
huge_pmd_share(mm, addr, pud);
pte = (pte_t *) pmd_alloc(mm, pud, addr);
}
}
BUG_ON(pte && !pte_none(*pte) && !pte_huge(*pte));
return pte;
}
pte_t *huge_pte_offset(struct mm_struct *mm, unsigned long addr)
{
pgd_t *pgd;
pud_t *pud;
pmd_t *pmd = NULL;
pgd = pgd_offset(mm, addr);
if (pgd_present(*pgd)) {
pud = pud_offset(pgd, addr);
if (pud_present(*pud)) {
if (pud_large(*pud))
return (pte_t *)pud;
pmd = pmd_offset(pud, addr);
}
}
return (pte_t *) pmd;
}
#if 0 /* This is just for testing */
struct page *
follow_huge_addr(struct mm_struct *mm, unsigned long address, int write)
{
unsigned long start = address;
int length = 1;
int nr;
struct page *page;
struct vm_area_struct *vma;
vma = find_vma(mm, addr);
if (!vma || !is_vm_hugetlb_page(vma))
return ERR_PTR(-EINVAL);
pte = huge_pte_offset(mm, address);
/* hugetlb should be locked, and hence, prefaulted */
WARN_ON(!pte || pte_none(*pte));
page = &pte_page(*pte)[vpfn % (HPAGE_SIZE/PAGE_SIZE)];
WARN_ON(!PageHead(page));
return page;
}
int pmd_huge(pmd_t pmd)
{
return 0;
}
int pud_huge(pud_t pud)
{
return 0;
}
struct page *
follow_huge_pmd(struct mm_struct *mm, unsigned long address,
pmd_t *pmd, int write)
{
return NULL;
}
#else
struct page *
follow_huge_addr(struct mm_struct *mm, unsigned long address, int write)
{
return ERR_PTR(-EINVAL);
}
int pmd_huge(pmd_t pmd)
{
return !!(pmd_val(pmd) & _PAGE_PSE);
}
int pud_huge(pud_t pud)
{
return !!(pud_val(pud) & _PAGE_PSE);
}
struct page *
follow_huge_pmd(struct mm_struct *mm, unsigned long address,
pmd_t *pmd, int write)
{
struct page *page;
page = pte_page(*(pte_t *)pmd);
if (page)
page += ((address & ~PMD_MASK) >> PAGE_SHIFT);
return page;
}
struct page *
follow_huge_pud(struct mm_struct *mm, unsigned long address,
pud_t *pud, int write)
{
struct page *page;
page = pte_page(*(pte_t *)pud);
if (page)
page += ((address & ~PUD_MASK) >> PAGE_SHIFT);
return page;
}
#endif
/* x86_64 also uses this file */
#ifdef HAVE_ARCH_HUGETLB_UNMAPPED_AREA
static unsigned long hugetlb_get_unmapped_area_bottomup(struct file *file,
unsigned long addr, unsigned long len,
unsigned long pgoff, unsigned long flags)
{
struct hstate *h = hstate_file(file);
struct mm_struct *mm = current->mm;
struct vm_area_struct *vma;
unsigned long start_addr;
if (len > mm->cached_hole_size) {
start_addr = mm->free_area_cache;
} else {
start_addr = TASK_UNMAPPED_BASE;
mm->cached_hole_size = 0;
}
full_search:
addr = ALIGN(start_addr, huge_page_size(h));
for (vma = find_vma(mm, addr); ; vma = vma->vm_next) {
/* At this point: (!vma || addr < vma->vm_end). */
if (TASK_SIZE - len < addr) {
/*
* Start a new search - just in case we missed
* some holes.
*/
if (start_addr != TASK_UNMAPPED_BASE) {
start_addr = TASK_UNMAPPED_BASE;
mm->cached_hole_size = 0;
goto full_search;
}
return -ENOMEM;
}
if (!vma || addr + len <= vma->vm_start) {
mm->free_area_cache = addr + len;
return addr;
}
if (addr + mm->cached_hole_size < vma->vm_start)
mm->cached_hole_size = vma->vm_start - addr;
addr = ALIGN(vma->vm_end, huge_page_size(h));
}
}
static unsigned long hugetlb_get_unmapped_area_topdown(struct file *file,
unsigned long addr0, unsigned long len,
unsigned long pgoff, unsigned long flags)
{
struct hstate *h = hstate_file(file);
struct mm_struct *mm = current->mm;
struct vm_area_struct *vma, *prev_vma;
unsigned long base = mm->mmap_base, addr = addr0;
unsigned long largest_hole = mm->cached_hole_size;
int first_time = 1;
/* don't allow allocations above current base */
if (mm->free_area_cache > base)
mm->free_area_cache = base;
if (len <= largest_hole) {
largest_hole = 0;
mm->free_area_cache = base;
}
try_again:
/* make sure it can fit in the remaining address space */
if (mm->free_area_cache < len)
goto fail;
/* either no address requested or cant fit in requested address hole */
addr = (mm->free_area_cache - len) & huge_page_mask(h);
do {
/*
* Lookup failure means no vma is above this address,
* i.e. return with success:
*/
if (!(vma = find_vma_prev(mm, addr, &prev_vma)))
return addr;
/*
* new region fits between prev_vma->vm_end and
* vma->vm_start, use it:
*/
if (addr + len <= vma->vm_start &&
(!prev_vma || (addr >= prev_vma->vm_end))) {
/* remember the address as a hint for next time */
mm->cached_hole_size = largest_hole;
return (mm->free_area_cache = addr);
} else {
/* pull free_area_cache down to the first hole */
if (mm->free_area_cache == vma->vm_end) {
mm->free_area_cache = vma->vm_start;
mm->cached_hole_size = largest_hole;
}
}
/* remember the largest hole we saw so far */
if (addr + largest_hole < vma->vm_start)
largest_hole = vma->vm_start - addr;
/* try just below the current vma->vm_start */
addr = (vma->vm_start - len) & huge_page_mask(h);
} while (len <= vma->vm_start);
fail:
/*
* if hint left us with no space for the requested
* mapping then try again:
*/
if (first_time) {
mm->free_area_cache = base;
largest_hole = 0;
first_time = 0;
goto try_again;
}
/*
* A failed mmap() very likely causes application failure,
* so fall back to the bottom-up function here. This scenario
* can happen with large stack limits and large mmap()
* allocations.
*/
mm->free_area_cache = TASK_UNMAPPED_BASE;
mm->cached_hole_size = ~0UL;
addr = hugetlb_get_unmapped_area_bottomup(file, addr0,
len, pgoff, flags);
/*
* Restore the topdown base:
*/
mm->free_area_cache = base;
mm->cached_hole_size = ~0UL;
return addr;
}
unsigned long
hugetlb_get_unmapped_area(struct file *file, unsigned long addr,
unsigned long len, unsigned long pgoff, unsigned long flags)
{
struct hstate *h = hstate_file(file);
struct mm_struct *mm = current->mm;
struct vm_area_struct *vma;
if (len & ~huge_page_mask(h))
return -EINVAL;
if (len > TASK_SIZE)
return -ENOMEM;
if (flags & MAP_FIXED) {
if (prepare_hugepage_range(file, addr, len))
return -EINVAL;
return addr;
}
if (addr) {
addr = ALIGN(addr, huge_page_size(h));
vma = find_vma(mm, addr);
if (TASK_SIZE - len >= addr &&
(!vma || addr + len <= vma->vm_start))
return addr;
}
if (mm->get_unmapped_area == arch_get_unmapped_area)
return hugetlb_get_unmapped_area_bottomup(file, addr, len,
pgoff, flags);
else
return hugetlb_get_unmapped_area_topdown(file, addr, len,
pgoff, flags);
}
#endif /*HAVE_ARCH_HUGETLB_UNMAPPED_AREA*/
#ifdef CONFIG_X86_64
static __init int setup_hugepagesz(char *opt)
{
unsigned long ps = memparse(opt, &opt);
if (ps == PMD_SIZE) {
hugetlb_add_hstate(PMD_SHIFT - PAGE_SHIFT);
} else if (ps == PUD_SIZE && cpu_has_gbpages) {
hugetlb_add_hstate(PUD_SHIFT - PAGE_SHIFT);
} else {
printk(KERN_ERR "hugepagesz: Unsupported page size %lu M\n",
ps >> 20);
return 0;
}
return 1;
}
__setup("hugepagesz=", setup_hugepagesz);
#endif