79 lines
2.6 KiB
Diff
79 lines
2.6 KiB
Diff
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From 799c10559d60f159ab2232203f222f18fa3c4a5f Mon Sep 17 00:00:00 2001
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From: Linus Torvalds <torvalds@linux-foundation.org>
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Date: Fri, 15 Oct 2010 11:09:28 -0700
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Subject: [PATCH] De-pessimize rds_page_copy_user
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Don't try to "optimize" rds_page_copy_user() by using kmap_atomic() and
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the unsafe atomic user mode accessor functions. It's actually slower
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than the straightforward code on any reasonable modern CPU.
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Back when the code was written (although probably not by the time it was
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actually merged, though), 32-bit x86 may have been the dominant
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architecture. And there kmap_atomic() can be a lot faster than kmap()
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(unless you have very good locality, in which case the virtual address
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caching by kmap() can overcome all the downsides).
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But these days, x86-64 may not be more populous, but it's getting there
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(and if you care about performance, it's definitely already there -
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you'd have upgraded your CPU's already in the last few years). And on
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x86-64, the non-kmap_atomic() version is faster, simply because the code
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is simpler and doesn't have the "re-try page fault" case.
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People with old hardware are not likely to care about RDS anyway, and
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the optimization for the 32-bit case is simply buggy, since it doesn't
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verify the user addresses properly.
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Reported-by: Dan Rosenberg <drosenberg@vsecurity.com>
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Acked-by: Andrew Morton <akpm@linux-foundation.org>
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Cc: stable@kernel.org
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Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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---
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net/rds/page.c | 27 +++++++--------------------
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1 files changed, 7 insertions(+), 20 deletions(-)
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diff --git a/net/rds/page.c b/net/rds/page.c
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index 595a952..1dfbfea 100644
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--- a/net/rds/page.c
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+++ b/net/rds/page.c
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@@ -57,30 +57,17 @@ int rds_page_copy_user(struct page *page, unsigned long offset,
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unsigned long ret;
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void *addr;
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- if (to_user)
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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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- else
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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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-
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- addr = kmap_atomic(page, KM_USER0);
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- if (to_user)
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- ret = __copy_to_user_inatomic(ptr, addr + offset, bytes);
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- else
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- ret = __copy_from_user_inatomic(addr + offset, ptr, bytes);
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- kunmap_atomic(addr, KM_USER0);
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-
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- if (ret) {
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- addr = kmap(page);
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- if (to_user)
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- ret = copy_to_user(ptr, addr + offset, bytes);
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- else
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- ret = copy_from_user(addr + offset, ptr, bytes);
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- kunmap(page);
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- if (ret)
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- return -EFAULT;
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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 0;
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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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1.7.3.2
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