linux/mm/filemap_xip.c
Ingo Molnar f180053694 x86, mm: dont use non-temporal stores in pagecache accesses
Impact: standardize IO on cached ops

On modern CPUs it is almost always a bad idea to use non-temporal stores,
as the regression in this commit has shown it:

  30d697f: x86: fix performance regression in write() syscall

The kernel simply has no good information about whether using non-temporal
stores is a good idea or not - and trying to add heuristics only increases
complexity and inserts fragility.

The regression on cached write()s took very long to be found - over two
years. So dont take any chances and let the hardware decide how it makes
use of its caches.

The only exception is drivers/gpu/drm/i915/i915_gem.c: there were we are
absolutely sure that another entity (the GPU) will pick up the dirty
data immediately and that the CPU will not touch that data before the
GPU will.

Also, keep the _nocache() primitives to make it easier for people to
experiment with these details. There may be more clear-cut cases where
non-cached copies can be used, outside of filemap.c.

Cc: Salman Qazi <sqazi@google.com>
Cc: Nick Piggin <npiggin@suse.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2009-03-02 11:06:49 +01:00

475 lines
11 KiB
C

/*
* linux/mm/filemap_xip.c
*
* Copyright (C) 2005 IBM Corporation
* Author: Carsten Otte <cotte@de.ibm.com>
*
* derived from linux/mm/filemap.c - Copyright (C) Linus Torvalds
*
*/
#include <linux/fs.h>
#include <linux/pagemap.h>
#include <linux/module.h>
#include <linux/uio.h>
#include <linux/rmap.h>
#include <linux/mmu_notifier.h>
#include <linux/sched.h>
#include <linux/seqlock.h>
#include <linux/mutex.h>
#include <asm/tlbflush.h>
#include <asm/io.h>
/*
* We do use our own empty page to avoid interference with other users
* of ZERO_PAGE(), such as /dev/zero
*/
static DEFINE_MUTEX(xip_sparse_mutex);
static seqcount_t xip_sparse_seq = SEQCNT_ZERO;
static struct page *__xip_sparse_page;
/* called under xip_sparse_mutex */
static struct page *xip_sparse_page(void)
{
if (!__xip_sparse_page) {
struct page *page = alloc_page(GFP_HIGHUSER | __GFP_ZERO);
if (page)
__xip_sparse_page = page;
}
return __xip_sparse_page;
}
/*
* This is a file read routine for execute in place files, and uses
* the mapping->a_ops->get_xip_mem() function for the actual low-level
* stuff.
*
* Note the struct file* is not used at all. It may be NULL.
*/
static ssize_t
do_xip_mapping_read(struct address_space *mapping,
struct file_ra_state *_ra,
struct file *filp,
char __user *buf,
size_t len,
loff_t *ppos)
{
struct inode *inode = mapping->host;
pgoff_t index, end_index;
unsigned long offset;
loff_t isize, pos;
size_t copied = 0, error = 0;
BUG_ON(!mapping->a_ops->get_xip_mem);
pos = *ppos;
index = pos >> PAGE_CACHE_SHIFT;
offset = pos & ~PAGE_CACHE_MASK;
isize = i_size_read(inode);
if (!isize)
goto out;
end_index = (isize - 1) >> PAGE_CACHE_SHIFT;
do {
unsigned long nr, left;
void *xip_mem;
unsigned long xip_pfn;
int zero = 0;
/* nr is the maximum number of bytes to copy from this page */
nr = PAGE_CACHE_SIZE;
if (index >= end_index) {
if (index > end_index)
goto out;
nr = ((isize - 1) & ~PAGE_CACHE_MASK) + 1;
if (nr <= offset) {
goto out;
}
}
nr = nr - offset;
if (nr > len)
nr = len;
error = mapping->a_ops->get_xip_mem(mapping, index, 0,
&xip_mem, &xip_pfn);
if (unlikely(error)) {
if (error == -ENODATA) {
/* sparse */
zero = 1;
} else
goto out;
}
/* If users can be writing to this page using arbitrary
* virtual addresses, take care about potential aliasing
* before reading the page on the kernel side.
*/
if (mapping_writably_mapped(mapping))
/* address based flush */ ;
/*
* Ok, we have the mem, so now we can copy it to user space...
*
* The actor routine returns how many bytes were actually used..
* NOTE! This may not be the same as how much of a user buffer
* we filled up (we may be padding etc), so we can only update
* "pos" here (the actor routine has to update the user buffer
* pointers and the remaining count).
*/
if (!zero)
left = __copy_to_user(buf+copied, xip_mem+offset, nr);
else
left = __clear_user(buf + copied, nr);
if (left) {
error = -EFAULT;
goto out;
}
copied += (nr - left);
offset += (nr - left);
index += offset >> PAGE_CACHE_SHIFT;
offset &= ~PAGE_CACHE_MASK;
} while (copied < len);
out:
*ppos = pos + copied;
if (filp)
file_accessed(filp);
return (copied ? copied : error);
}
ssize_t
xip_file_read(struct file *filp, char __user *buf, size_t len, loff_t *ppos)
{
if (!access_ok(VERIFY_WRITE, buf, len))
return -EFAULT;
return do_xip_mapping_read(filp->f_mapping, &filp->f_ra, filp,
buf, len, ppos);
}
EXPORT_SYMBOL_GPL(xip_file_read);
/*
* __xip_unmap is invoked from xip_unmap and
* xip_write
*
* This function walks all vmas of the address_space and unmaps the
* __xip_sparse_page when found at pgoff.
*/
static void
__xip_unmap (struct address_space * mapping,
unsigned long pgoff)
{
struct vm_area_struct *vma;
struct mm_struct *mm;
struct prio_tree_iter iter;
unsigned long address;
pte_t *pte;
pte_t pteval;
spinlock_t *ptl;
struct page *page;
unsigned count;
int locked = 0;
count = read_seqcount_begin(&xip_sparse_seq);
page = __xip_sparse_page;
if (!page)
return;
retry:
spin_lock(&mapping->i_mmap_lock);
vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, pgoff, pgoff) {
mm = vma->vm_mm;
address = vma->vm_start +
((pgoff - vma->vm_pgoff) << PAGE_SHIFT);
BUG_ON(address < vma->vm_start || address >= vma->vm_end);
pte = page_check_address(page, mm, address, &ptl, 1);
if (pte) {
/* Nuke the page table entry. */
flush_cache_page(vma, address, pte_pfn(*pte));
pteval = ptep_clear_flush_notify(vma, address, pte);
page_remove_rmap(page);
dec_mm_counter(mm, file_rss);
BUG_ON(pte_dirty(pteval));
pte_unmap_unlock(pte, ptl);
page_cache_release(page);
}
}
spin_unlock(&mapping->i_mmap_lock);
if (locked) {
mutex_unlock(&xip_sparse_mutex);
} else if (read_seqcount_retry(&xip_sparse_seq, count)) {
mutex_lock(&xip_sparse_mutex);
locked = 1;
goto retry;
}
}
/*
* xip_fault() is invoked via the vma operations vector for a
* mapped memory region to read in file data during a page fault.
*
* This function is derived from filemap_fault, but used for execute in place
*/
static int xip_file_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
{
struct file *file = vma->vm_file;
struct address_space *mapping = file->f_mapping;
struct inode *inode = mapping->host;
pgoff_t size;
void *xip_mem;
unsigned long xip_pfn;
struct page *page;
int error;
/* XXX: are VM_FAULT_ codes OK? */
again:
size = (i_size_read(inode) + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
if (vmf->pgoff >= size)
return VM_FAULT_SIGBUS;
error = mapping->a_ops->get_xip_mem(mapping, vmf->pgoff, 0,
&xip_mem, &xip_pfn);
if (likely(!error))
goto found;
if (error != -ENODATA)
return VM_FAULT_OOM;
/* sparse block */
if ((vma->vm_flags & (VM_WRITE | VM_MAYWRITE)) &&
(vma->vm_flags & (VM_SHARED | VM_MAYSHARE)) &&
(!(mapping->host->i_sb->s_flags & MS_RDONLY))) {
int err;
/* maybe shared writable, allocate new block */
mutex_lock(&xip_sparse_mutex);
error = mapping->a_ops->get_xip_mem(mapping, vmf->pgoff, 1,
&xip_mem, &xip_pfn);
mutex_unlock(&xip_sparse_mutex);
if (error)
return VM_FAULT_SIGBUS;
/* unmap sparse mappings at pgoff from all other vmas */
__xip_unmap(mapping, vmf->pgoff);
found:
err = vm_insert_mixed(vma, (unsigned long)vmf->virtual_address,
xip_pfn);
if (err == -ENOMEM)
return VM_FAULT_OOM;
BUG_ON(err);
return VM_FAULT_NOPAGE;
} else {
int err, ret = VM_FAULT_OOM;
mutex_lock(&xip_sparse_mutex);
write_seqcount_begin(&xip_sparse_seq);
error = mapping->a_ops->get_xip_mem(mapping, vmf->pgoff, 0,
&xip_mem, &xip_pfn);
if (unlikely(!error)) {
write_seqcount_end(&xip_sparse_seq);
mutex_unlock(&xip_sparse_mutex);
goto again;
}
if (error != -ENODATA)
goto out;
/* not shared and writable, use xip_sparse_page() */
page = xip_sparse_page();
if (!page)
goto out;
err = vm_insert_page(vma, (unsigned long)vmf->virtual_address,
page);
if (err == -ENOMEM)
goto out;
ret = VM_FAULT_NOPAGE;
out:
write_seqcount_end(&xip_sparse_seq);
mutex_unlock(&xip_sparse_mutex);
return ret;
}
}
static struct vm_operations_struct xip_file_vm_ops = {
.fault = xip_file_fault,
};
int xip_file_mmap(struct file * file, struct vm_area_struct * vma)
{
BUG_ON(!file->f_mapping->a_ops->get_xip_mem);
file_accessed(file);
vma->vm_ops = &xip_file_vm_ops;
vma->vm_flags |= VM_CAN_NONLINEAR | VM_MIXEDMAP;
return 0;
}
EXPORT_SYMBOL_GPL(xip_file_mmap);
static ssize_t
__xip_file_write(struct file *filp, const char __user *buf,
size_t count, loff_t pos, loff_t *ppos)
{
struct address_space * mapping = filp->f_mapping;
const struct address_space_operations *a_ops = mapping->a_ops;
struct inode *inode = mapping->host;
long status = 0;
size_t bytes;
ssize_t written = 0;
BUG_ON(!mapping->a_ops->get_xip_mem);
do {
unsigned long index;
unsigned long offset;
size_t copied;
void *xip_mem;
unsigned long xip_pfn;
offset = (pos & (PAGE_CACHE_SIZE -1)); /* Within page */
index = pos >> PAGE_CACHE_SHIFT;
bytes = PAGE_CACHE_SIZE - offset;
if (bytes > count)
bytes = count;
status = a_ops->get_xip_mem(mapping, index, 0,
&xip_mem, &xip_pfn);
if (status == -ENODATA) {
/* we allocate a new page unmap it */
mutex_lock(&xip_sparse_mutex);
status = a_ops->get_xip_mem(mapping, index, 1,
&xip_mem, &xip_pfn);
mutex_unlock(&xip_sparse_mutex);
if (!status)
/* unmap page at pgoff from all other vmas */
__xip_unmap(mapping, index);
}
if (status)
break;
copied = bytes -
__copy_from_user_nocache(xip_mem + offset, buf, bytes);
if (likely(copied > 0)) {
status = copied;
if (status >= 0) {
written += status;
count -= status;
pos += status;
buf += status;
}
}
if (unlikely(copied != bytes))
if (status >= 0)
status = -EFAULT;
if (status < 0)
break;
} while (count);
*ppos = pos;
/*
* No need to use i_size_read() here, the i_size
* cannot change under us because we hold i_mutex.
*/
if (pos > inode->i_size) {
i_size_write(inode, pos);
mark_inode_dirty(inode);
}
return written ? written : status;
}
ssize_t
xip_file_write(struct file *filp, const char __user *buf, size_t len,
loff_t *ppos)
{
struct address_space *mapping = filp->f_mapping;
struct inode *inode = mapping->host;
size_t count;
loff_t pos;
ssize_t ret;
mutex_lock(&inode->i_mutex);
if (!access_ok(VERIFY_READ, buf, len)) {
ret=-EFAULT;
goto out_up;
}
pos = *ppos;
count = len;
vfs_check_frozen(inode->i_sb, SB_FREEZE_WRITE);
/* We can write back this queue in page reclaim */
current->backing_dev_info = mapping->backing_dev_info;
ret = generic_write_checks(filp, &pos, &count, S_ISBLK(inode->i_mode));
if (ret)
goto out_backing;
if (count == 0)
goto out_backing;
ret = file_remove_suid(filp);
if (ret)
goto out_backing;
file_update_time(filp);
ret = __xip_file_write (filp, buf, count, pos, ppos);
out_backing:
current->backing_dev_info = NULL;
out_up:
mutex_unlock(&inode->i_mutex);
return ret;
}
EXPORT_SYMBOL_GPL(xip_file_write);
/*
* truncate a page used for execute in place
* functionality is analog to block_truncate_page but does use get_xip_mem
* to get the page instead of page cache
*/
int
xip_truncate_page(struct address_space *mapping, loff_t from)
{
pgoff_t index = from >> PAGE_CACHE_SHIFT;
unsigned offset = from & (PAGE_CACHE_SIZE-1);
unsigned blocksize;
unsigned length;
void *xip_mem;
unsigned long xip_pfn;
int err;
BUG_ON(!mapping->a_ops->get_xip_mem);
blocksize = 1 << mapping->host->i_blkbits;
length = offset & (blocksize - 1);
/* Block boundary? Nothing to do */
if (!length)
return 0;
length = blocksize - length;
err = mapping->a_ops->get_xip_mem(mapping, index, 0,
&xip_mem, &xip_pfn);
if (unlikely(err)) {
if (err == -ENODATA)
/* Hole? No need to truncate */
return 0;
else
return err;
}
memset(xip_mem + offset, 0, length);
return 0;
}
EXPORT_SYMBOL_GPL(xip_truncate_page);