From mboxrd@z Thu Jan 1 00:00:00 1970 From: gmbnomis@gmail.com (Simon Baatz) Date: Wed, 26 Sep 2012 23:40:57 +0200 Subject: [PATCH 0/2] fix and improvement of flush(_kernel)_dcache_page() Message-ID: <1348695659-27603-1-git-send-email-gmbnomis@gmail.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org Hi, another attempt to fix the regression caused by patch f8b63c1 "ARM: 6382/1" in 2.6.37 (see [2]). The problem occurs on VIVT (and probably VIPT aliasing) cache architectures for drivers that use flush_kernel_dcache_page(). For example, 3.6-rc6 (as any kernel beginning with 2.6.37) on kirkwood using mv_cesa produces data corruption when using direct I/O: ~# cryptsetup luksOpen /dev/sda2 c_sda2 Enter passphrase for /dev/sda2: ~# dd if=/dev/mapper/c_sda2 iflag=direct bs=4k count=16 2>/dev/null | sha1sum 9ae4997ec85ad9b7ab4b10341e42ace80f0ea5d6 - ~# dd if=/dev/mapper/c_sda2 bs=4k count=16 2>/dev/null | sha1sum ca39c5d4950b3704eff952c48e383bf1db20532e - (The mv_cesa driver uses the scatterlist memory iterator, which uses flush_kernel_dcache_page() before kunmap()). As described in [1], both flush_dcache_page() and flush_kernel_dcache_page() need to handle the following cases: - page cache pages with no user space mapping - page cache pages with user space mapping(s) - flush the kernel mapping of anonymous pages The last one is contradictory to documentation for flush_dcache_page(), but many uses in the kernel require it (drivers use it to flush modifications via the kernel mapping). In the proposed patch the implementation of flush_kernel_dcache_page() follows the one of flush_dcache_page(), but only flushes the kernel mapping, not the user mapping(s). The second patch optimizes these two functions for non-aliasing VIPT caches. On these the flush of the kernel mapping for the anon case is actually not needed. It may be needed to ensure I/D coherency, but this can be handled by __sync_icache_dcache() later and more effectively (similar to arm64, see [3]). Thus, we should be lazy as well here and just clear the PG_dcache_clean bit. I could only test this on kirkwood (ARMv5, VIVT) and raspberry pi BCM2835 (ARMv6, PIPT / VIPT nonaliasing data cache). More testing would probably be a good thing... Especially, I could not test the non-aliasing cache case with a real driver using flush_kernel_dcache_page() (mv_cesa on dove could be a test case for this). - Simon [1] http://lists.infradead.org/pipermail/linux-arm-kernel/2012-August/113908.html [2] http://lists.infradead.org/pipermail/linux-arm-kernel/2012-May/101795.html [3] https://lkml.org/lkml/2012/9/12/121 Simon Baatz (2): ARM: Handle user space mapped pages in flush_kernel_dcache_page ARM: remove unnecessary flush of anon pages in flush(_kernel)_dcache_page() arch/arm/include/asm/cacheflush.h | 4 ++ arch/arm/mm/flush.c | 83 +++++++++++++++++++++++++++++-------- 2 files changed, 70 insertions(+), 17 deletions(-) -- 1.7.9.5