linux-kernel - Re: [PATCH v5 2/6] dax: fix cache flush on PMD-mapped pages

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Date:   Tue, 22 Mar 2022 01:34:24 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Muchun Song <songmuchun@...edance.com>
Cc:     dan.j.williams@...el.com, willy@...radead.org, jack@...e.cz,
        viro@...iv.linux.org.uk, akpm@...ux-foundation.org,
        apopple@...dia.com, shy828301@...il.com, rcampbell@...dia.com,
        hughd@...gle.com, xiyuyang19@...an.edu.cn,
        kirill.shutemov@...ux.intel.com, zwisler@...nel.org,
        hch@...radead.org, linux-fsdevel@...r.kernel.org,
        nvdimm@...ts.linux.dev, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, duanxiongchun@...edance.com, smuchun@...il.com
Subject: Re: [PATCH v5 2/6] dax: fix cache flush on PMD-mapped pages

On Fri, Mar 18, 2022 at 03:45:25PM +0800, Muchun Song wrote:
> The flush_cache_page() only remove a PAGE_SIZE sized range from the cache.
> However, it does not cover the full pages in a THP except a head page.
> Replace it with flush_cache_range() to fix this issue.  This is just a
> documentation issue with the respect to properly documenting the expected
> usage of cache flushing before modifying the pmd.  However, in practice
> this is not a problem due to the fact that DAX is not available on
> architectures with virtually indexed caches per:
> 
>   commit d92576f1167c ("dax: does not work correctly with virtual aliasing caches")
> 
> Fixes: f729c8c9b24f ("dax: wrprotect pmd_t in dax_mapping_entry_mkclean")
> Signed-off-by: Muchun Song <songmuchun@...edance.com>
> Reviewed-by: Dan Williams <dan.j.williams@...el.com>

Looks good:

Reviewed-by: Christoph Hellwig <hch@....de>