Messages in this thread | | | Date | Tue, 26 Jan 2010 09:01:10 +0800 | Subject | Re: [PATCH] Flush dcache before writing into page to avoid alias | From | anfei zhou <> |
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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. > > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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