linux-kernel - Re: [PATCH v4 2/6] dax: fix cache flush on PMD-mapped pages

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Date:   Wed, 9 Mar 2022 16:06:05 -0800
From:   Dan Williams <dan.j.williams@...el.com>
To:     Muchun Song <songmuchun@...edance.com>
Cc:     Matthew Wilcox <willy@...radead.org>, Jan Kara <jack@...e.cz>,
        Al Viro <viro@...iv.linux.org.uk>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Alistair Popple <apopple@...dia.com>,
        Yang Shi <shy828301@...il.com>,
        Ralph Campbell <rcampbell@...dia.com>,
        Hugh Dickins <hughd@...gle.com>, xiyuyang19@...an.edu.cn,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Ross Zwisler <zwisler@...nel.org>,
        Christoph Hellwig <hch@...radead.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Linux NVDIMM <nvdimm@...ts.linux.dev>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux MM <linux-mm@...ck.org>, duanxiongchun@...edance.com,
        Muchun Song <smuchun@...il.com>
Subject: Re: [PATCH v4 2/6] dax: fix cache flush on PMD-mapped pages

On Wed, Mar 2, 2022 at 12:29 AM Muchun Song <songmuchun@...edance.com> 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 needs to clarify that 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:

d92576f1167c dax: does not work correctly with virtual aliasing caches

Otherwise, you can add:

Reviewed-by: Dan Williams <dan.j.williams@...el.com>