Re: flush_kernel_dcache_page fixes and removal

From: Guo Ren
Date: Tue Jul 13 2021 - 23:13:26 EST


Acked-by for csky abiv1 part.(No change to our execution path after
the patch set.)

On Mon, Jul 12, 2021 at 2:10 PM Christoph Hellwig <hch@xxxxxx> wrote:
>
> Hi all,
>
> while looking to convert the block layer away from kmap_atomic towards
> kmap_local_page and prefeably the helpers that abstract it away I noticed
> that a few block drivers directly or implicitly call
> flush_kernel_dcache_page before kunmapping a page that has been written
> to. flush_kernel_dcache_page is documented to to be used in such cases,
> but flush_dcache_page is actually required when the page could be in
> the page cache and mapped to userspace, which is pretty much always the
> case when kmapping an arbitrary page. Unfortunately the documentation
> doesn't exactly make that clear, which lead to this misused. And it turns
> out that only the copy_strings / copy_string_kernel in the exec code
> were actually correct users of flush_kernel_dcache_page, which is why
> I think we should just remove it and eat the very minor overhead in
> exec rather than confusing poor driver writers.
>
> Diffstat:
> Documentation/core-api/cachetlb.rst | 86 +++++++----------
> Documentation/translations/zh_CN/core-api/cachetlb.rst | 9 -
> arch/arm/include/asm/cacheflush.h | 4
> arch/arm/mm/flush.c | 33 ------
> arch/arm/mm/nommu.c | 6 -
> arch/csky/abiv1/cacheflush.c | 11 --
> arch/csky/abiv1/inc/abi/cacheflush.h | 4
> arch/mips/include/asm/cacheflush.h | 8 -
> arch/nds32/include/asm/cacheflush.h | 3
> arch/nds32/mm/cacheflush.c | 9 -
> arch/parisc/include/asm/cacheflush.h | 8 -
> arch/parisc/kernel/cache.c | 3
> arch/sh/include/asm/cacheflush.h | 8 -
> block/blk-map.c | 2
> drivers/block/ps3disk.c | 2
> drivers/mmc/host/jz4740_mmc.c | 4
> drivers/mmc/host/mmc_spi.c | 2
> drivers/scsi/aacraid/aachba.c | 1
> fs/exec.c | 6 -
> include/linux/highmem.h | 5
> lib/scatterlist.c | 5
> tools/testing/scatterlist/linux/mm.h | 1
> 22 files changed, 55 insertions(+), 165 deletions(-)



--
Best Regards
Guo Ren

ML: https://lore.kernel.org/linux-csky/