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![Linus Torvalds](/assets/img/avatar_default.png)
Don't try to "optimize" rds_page_copy_user() by using kmap_atomic() and the unsafe atomic user mode accessor functions. It's actually slower than the straightforward code on any reasonable modern CPU. Back when the code was written (although probably not by the time it was actually merged, though), 32-bit x86 may have been the dominant architecture. And there kmap_atomic() can be a lot faster than kmap() (unless you have very good locality, in which case the virtual address caching by kmap() can overcome all the downsides). But these days, x86-64 may not be more populous, but it's getting there (and if you care about performance, it's definitely already there - you'd have upgraded your CPU's already in the last few years). And on x86-64, the non-kmap_atomic() version is faster, simply because the code is simpler and doesn't have the "re-try page fault" case. People with old hardware are not likely to care about RDS anyway, and the optimization for the 32-bit case is simply buggy, since it doesn't verify the user addresses properly. Reported-by: Dan Rosenberg <drosenberg@vsecurity.com> Acked-by: Andrew Morton <akpm@linux-foundation.org> Cc: stable@kernel.org Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
210 lines
5.7 KiB
C
210 lines
5.7 KiB
C
/*
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* Copyright (c) 2006 Oracle. All rights reserved.
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*
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* This software is available to you under a choice of one of two
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* licenses. You may choose to be licensed under the terms of the GNU
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* General Public License (GPL) Version 2, available from the file
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* COPYING in the main directory of this source tree, or the
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* OpenIB.org BSD license below:
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*
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* Redistribution and use in source and binary forms, with or
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* without modification, are permitted provided that the following
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* conditions are met:
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*
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* - Redistributions of source code must retain the above
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* copyright notice, this list of conditions and the following
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* disclaimer.
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*
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* - Redistributions in binary form must reproduce the above
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* copyright notice, this list of conditions and the following
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* disclaimer in the documentation and/or other materials
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* provided with the distribution.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
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* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
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* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
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* NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
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* BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
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* ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
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* CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
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* SOFTWARE.
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*
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*/
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#include <linux/highmem.h>
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#include <linux/gfp.h>
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#include "rds.h"
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struct rds_page_remainder {
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struct page *r_page;
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unsigned long r_offset;
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};
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DEFINE_PER_CPU_SHARED_ALIGNED(struct rds_page_remainder, rds_page_remainders);
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/*
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* returns 0 on success or -errno on failure.
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*
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* We don't have to worry about flush_dcache_page() as this only works
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* with private pages. If, say, we were to do directed receive to pinned
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* user pages we'd have to worry more about cache coherence. (Though
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* the flush_dcache_page() in get_user_pages() would probably be enough).
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*/
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int rds_page_copy_user(struct page *page, unsigned long offset,
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void __user *ptr, unsigned long bytes,
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int to_user)
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{
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unsigned long ret;
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void *addr;
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addr = kmap(page);
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if (to_user) {
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rds_stats_add(s_copy_to_user, bytes);
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ret = copy_to_user(ptr, addr + offset, bytes);
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} else {
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rds_stats_add(s_copy_from_user, bytes);
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ret = copy_from_user(addr + offset, ptr, bytes);
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}
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kunmap(page);
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return ret ? -EFAULT : 0;
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}
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EXPORT_SYMBOL_GPL(rds_page_copy_user);
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/*
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* Message allocation uses this to build up regions of a message.
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*
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* @bytes - the number of bytes needed.
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* @gfp - the waiting behaviour of the allocation
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*
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* @gfp is always ored with __GFP_HIGHMEM. Callers must be prepared to
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* kmap the pages, etc.
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*
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* If @bytes is at least a full page then this just returns a page from
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* alloc_page().
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*
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* If @bytes is a partial page then this stores the unused region of the
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* page in a per-cpu structure. Future partial-page allocations may be
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* satisfied from that cached region. This lets us waste less memory on
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* small allocations with minimal complexity. It works because the transmit
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* path passes read-only page regions down to devices. They hold a page
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* reference until they are done with the region.
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*/
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int rds_page_remainder_alloc(struct scatterlist *scat, unsigned long bytes,
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gfp_t gfp)
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{
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struct rds_page_remainder *rem;
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unsigned long flags;
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struct page *page;
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int ret;
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gfp |= __GFP_HIGHMEM;
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/* jump straight to allocation if we're trying for a huge page */
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if (bytes >= PAGE_SIZE) {
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page = alloc_page(gfp);
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if (page == NULL) {
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ret = -ENOMEM;
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} else {
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sg_set_page(scat, page, PAGE_SIZE, 0);
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ret = 0;
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}
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goto out;
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}
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rem = &per_cpu(rds_page_remainders, get_cpu());
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local_irq_save(flags);
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while (1) {
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/* avoid a tiny region getting stuck by tossing it */
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if (rem->r_page && bytes > (PAGE_SIZE - rem->r_offset)) {
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rds_stats_inc(s_page_remainder_miss);
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__free_page(rem->r_page);
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rem->r_page = NULL;
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}
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/* hand out a fragment from the cached page */
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if (rem->r_page && bytes <= (PAGE_SIZE - rem->r_offset)) {
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sg_set_page(scat, rem->r_page, bytes, rem->r_offset);
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get_page(sg_page(scat));
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if (rem->r_offset != 0)
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rds_stats_inc(s_page_remainder_hit);
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rem->r_offset += bytes;
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if (rem->r_offset == PAGE_SIZE) {
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__free_page(rem->r_page);
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rem->r_page = NULL;
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}
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ret = 0;
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break;
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}
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/* alloc if there is nothing for us to use */
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local_irq_restore(flags);
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put_cpu();
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page = alloc_page(gfp);
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rem = &per_cpu(rds_page_remainders, get_cpu());
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local_irq_save(flags);
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if (page == NULL) {
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ret = -ENOMEM;
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break;
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}
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/* did someone race to fill the remainder before us? */
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if (rem->r_page) {
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__free_page(page);
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continue;
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}
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/* otherwise install our page and loop around to alloc */
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rem->r_page = page;
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rem->r_offset = 0;
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}
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local_irq_restore(flags);
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put_cpu();
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out:
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rdsdebug("bytes %lu ret %d %p %u %u\n", bytes, ret,
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ret ? NULL : sg_page(scat), ret ? 0 : scat->offset,
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ret ? 0 : scat->length);
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return ret;
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}
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static int rds_page_remainder_cpu_notify(struct notifier_block *self,
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unsigned long action, void *hcpu)
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{
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struct rds_page_remainder *rem;
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long cpu = (long)hcpu;
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rem = &per_cpu(rds_page_remainders, cpu);
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rdsdebug("cpu %ld action 0x%lx\n", cpu, action);
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switch (action) {
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case CPU_DEAD:
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if (rem->r_page)
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__free_page(rem->r_page);
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rem->r_page = NULL;
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break;
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}
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return 0;
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}
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static struct notifier_block rds_page_remainder_nb = {
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.notifier_call = rds_page_remainder_cpu_notify,
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};
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void rds_page_exit(void)
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{
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int i;
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for_each_possible_cpu(i)
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rds_page_remainder_cpu_notify(&rds_page_remainder_nb,
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(unsigned long)CPU_DEAD,
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(void *)(long)i);
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}
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