Messages in this thread | | | Date | Wed, 27 Jan 2010 22:59:59 +0100 | From | Sebastian Andrzej Siewior <> | Subject | Re: [PATCH] Flush dcache before writing into page to avoid alias |
| |
* 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
| |