* [PATCH] Flush dcache before writing into page to avoid alias [not found] ` <20100125133308.GA26799@desktop> @ 2010-01-25 19:58 ` Andrew Morton 2010-01-25 20:00 ` Russell King - ARM Linux 2010-01-26 1:01 ` anfei zhou 0 siblings, 2 replies; 5+ messages in thread From: Andrew Morton @ 2010-01-25 19:58 UTC (permalink / raw) To: linux-arm-kernel On Mon, 25 Jan 2010 21:33:08 +0800 anfei <anfei.zhou@gmail.com> wrote: > Hi Andrew, > > On Thu, Jan 21, 2010 at 01:07:57PM +0800, anfei zhou wrote: > > The cache alias problem will happen if the changes of user shared mapping > > is not flushed before copying, then user and kernel mapping may be mapped > > into two different cache line, it is impossible to guarantee the coherence > > after iov_iter_copy_from_user_atomic. So the right steps should be: > > flush_dcache_page(page); > > kmap_atomic(page); > > write to page; > > kunmap_atomic(page); > > flush_dcache_page(page); > > More precisely, we might create two new APIs flush_dcache_user_page and > > flush_dcache_kern_page to replace the two flush_dcache_page accordingly. > > > > Here is a snippet tested on omap2430 with VIPT cache, and I think it is > > not ARM-specific: > > int val = 0x11111111; > > fd = open("abc", O_RDWR); > > addr = mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0); > > *(addr+0) = 0x44444444; > > tmp = *(addr+0); > > *(addr+1) = 0x77777777; > > write(fd, &val, sizeof(int)); > > close(fd); > > The results are not always 0x11111111 0x77777777 at the beginning as expected. > > > Is this a real bug or not necessary to support? Bug. If variable `addr' has type int* then the contents of that file should be 0x11111111 0x77777777. You didn't tell us what the contents were in the incorrect case, but I guess it doesn't matter. ^ permalink raw reply [flat|nested] 5+ messages in thread
* [PATCH] Flush dcache before writing into page to avoid alias 2010-01-25 19:58 ` [PATCH] Flush dcache before writing into page to avoid alias Andrew Morton @ 2010-01-25 20:00 ` Russell King - ARM Linux 2010-01-27 21:59 ` Sebastian Andrzej Siewior 2010-01-26 1:01 ` anfei zhou 1 sibling, 1 reply; 5+ messages in thread From: Russell King - ARM Linux @ 2010-01-25 20:00 UTC (permalink / raw) To: linux-arm-kernel On Mon, Jan 25, 2010 at 11:58:14AM -0800, Andrew Morton wrote: > On Mon, 25 Jan 2010 21:33:08 +0800 anfei <anfei.zhou@gmail.com> wrote: > > > Hi Andrew, > > > > On Thu, Jan 21, 2010 at 01:07:57PM +0800, anfei zhou wrote: > > > The cache alias problem will happen if the changes of user shared mapping > > > is not flushed before copying, then user and kernel mapping may be mapped > > > into two different cache line, it is impossible to guarantee the coherence > > > after iov_iter_copy_from_user_atomic. So the right steps should be: > > > flush_dcache_page(page); > > > kmap_atomic(page); > > > write to page; > > > kunmap_atomic(page); > > > flush_dcache_page(page); > > > More precisely, we might create two new APIs flush_dcache_user_page and > > > flush_dcache_kern_page to replace the two flush_dcache_page accordingly. > > > > > > Here is a snippet tested on omap2430 with VIPT cache, and I think it is > > > not ARM-specific: > > > int val = 0x11111111; > > > fd = open("abc", O_RDWR); > > > addr = mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0); > > > *(addr+0) = 0x44444444; > > > tmp = *(addr+0); > > > *(addr+1) = 0x77777777; > > > write(fd, &val, sizeof(int)); > > > close(fd); > > > The results are not always 0x11111111 0x77777777 at the beginning as expected. > > > > > Is this a real bug or not necessary to support? > > Bug. If variable `addr' has type int* then the contents of that file > should be 0x11111111 0x77777777. You didn't tell us what the contents > were in the incorrect case, but I guess it doesn't matter. FYI, from a previous email from anfei: 0x44444444 0x77777777 ^ permalink raw reply [flat|nested] 5+ messages in thread
* [PATCH] Flush dcache before writing into page to avoid alias 2010-01-25 20:00 ` Russell King - ARM Linux @ 2010-01-27 21:59 ` Sebastian Andrzej Siewior 2010-01-27 22:12 ` Andrew Morton 0 siblings, 1 reply; 5+ messages in thread From: Sebastian Andrzej Siewior @ 2010-01-27 21:59 UTC (permalink / raw) To: linux-arm-kernel * Russell King - ARM Linux | 2010-01-25 20:00:04 [+0000]: >On Mon, Jan 25, 2010 at 11:58:14AM -0800, Andrew Morton wrote: >> On Mon, 25 Jan 2010 21:33:08 +0800 anfei <anfei.zhou@gmail.com> wrote: >> >> > Hi Andrew, >> > >> > On Thu, Jan 21, 2010 at 01:07:57PM +0800, anfei zhou wrote: >> > > The cache alias problem will happen if the changes of user shared mapping >> > > is not flushed before copying, then user and kernel mapping may be mapped >> > > into two different cache line, it is impossible to guarantee the coherence >> > > after iov_iter_copy_from_user_atomic. So the right steps should be: >> > > flush_dcache_page(page); >> > > kmap_atomic(page); >> > > write to page; >> > > kunmap_atomic(page); >> > > flush_dcache_page(page); >> > > More precisely, we might create two new APIs flush_dcache_user_page and >> > > flush_dcache_kern_page to replace the two flush_dcache_page accordingly. >> > > >> > > Here is a snippet tested on omap2430 with VIPT cache, and I think it is >> > > not ARM-specific: >> > > int val = 0x11111111; >> > > fd = open("abc", O_RDWR); >> > > addr = mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0); >> > > *(addr+0) = 0x44444444; >> > > tmp = *(addr+0); >> > > *(addr+1) = 0x77777777; >> > > write(fd, &val, sizeof(int)); >> > > close(fd); >> > > The results are not always 0x11111111 0x77777777 at the beginning as expected. >> > > >> > Is this a real bug or not necessary to support? >> >> Bug. If variable `addr' has type int* then the contents of that file >> should be 0x11111111 0x77777777. You didn't tell us what the contents >> were in the incorrect case, but I guess it doesn't matter. > >FYI, from a previous email from anfei: > >0x44444444 0x77777777 I just wanted to query what the status of this patch is. This patch seems to fix a real bug which causes a test suite to fail on ARM [0]. The test suite passes on my VIVT ARM with this patch. [0] http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=524003 Sebastian ^ permalink raw reply [flat|nested] 5+ messages in thread
* [PATCH] Flush dcache before writing into page to avoid alias 2010-01-27 21:59 ` Sebastian Andrzej Siewior @ 2010-01-27 22:12 ` Andrew Morton 0 siblings, 0 replies; 5+ messages in thread From: Andrew Morton @ 2010-01-27 22:12 UTC (permalink / raw) To: linux-arm-kernel On Wed, 27 Jan 2010 22:59:59 +0100 Sebastian Andrzej Siewior <sebastian@breakpoint.cc> wrote: > I just wanted to query what the status of this patch is. This patch > seems to fix a real bug which causes a test suite to fail on ARM [0]. > The test suite passes on my VIVT ARM with this patch. > > [0] http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=524003 I have it queued for 2.6.33, backportable to 2.6.32.x, assuming that nobody sees any issues with it. ^ permalink raw reply [flat|nested] 5+ messages in thread
* [PATCH] Flush dcache before writing into page to avoid alias 2010-01-25 19:58 ` [PATCH] Flush dcache before writing into page to avoid alias Andrew Morton 2010-01-25 20:00 ` Russell King - ARM Linux @ 2010-01-26 1:01 ` anfei zhou 1 sibling, 0 replies; 5+ messages in thread From: anfei zhou @ 2010-01-26 1:01 UTC (permalink / raw) To: linux-arm-kernel On Tue, Jan 26, 2010 at 3:58 AM, Andrew Morton <akpm@linux-foundation.org> wrote: > On Mon, 25 Jan 2010 21:33:08 +0800 anfei <anfei.zhou@gmail.com> wrote: > >> Hi Andrew, >> >> On Thu, Jan 21, 2010 at 01:07:57PM +0800, anfei zhou wrote: >> > The cache alias problem will happen if the changes of user shared mapping >> > is not flushed before copying, then user and kernel mapping may be mapped >> > into two different cache line, it is impossible to guarantee the coherence >> > after iov_iter_copy_from_user_atomic. ?So the right steps should be: >> > ? ? flush_dcache_page(page); >> > ? ? kmap_atomic(page); >> > ? ? write to page; >> > ? ? kunmap_atomic(page); >> > ? ? flush_dcache_page(page); >> > More precisely, we might create two new APIs flush_dcache_user_page and >> > flush_dcache_kern_page to replace the two flush_dcache_page accordingly. >> > >> > Here is a snippet tested on omap2430 with VIPT cache, and I think it is >> > not ARM-specific: >> > ? ? int val = 0x11111111; >> > ? ? fd = open("abc", O_RDWR); >> > ? ? addr = mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0); >> > ? ? *(addr+0) = 0x44444444; >> > ? ? tmp = *(addr+0); >> > ? ? *(addr+1) = 0x77777777; >> > ? ? write(fd, &val, sizeof(int)); >> > ? ? close(fd); >> > The results are not always 0x11111111 0x77777777 at the beginning as expected. >> > >> Is this a real bug or not necessary to support? > > Bug. ?If variable `addr' has type int* then the contents of that file > should be 0x11111111 0x77777777. ?You didn't tell us what the contents > were in the incorrect case, but I guess it doesn't matter. > Sorry, I didn't give the details, here is the old thread with more details: http://linux.derkeiler.com/Mailing-Lists/Kernel/2010-01/msg07124.html Regards, Anfei. > > ^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2010-01-27 22:12 UTC | newest]
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[not found] ` <20100125133308.GA26799@desktop>
2010-01-25 19:58 ` [PATCH] Flush dcache before writing into page to avoid alias Andrew Morton
2010-01-25 20:00 ` Russell King - ARM Linux
2010-01-27 21:59 ` Sebastian Andrzej Siewior
2010-01-27 22:12 ` Andrew Morton
2010-01-26 1:01 ` anfei zhou
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