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

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Message-ID: <CAMZfGtUNRAb3qnx5-ZV1uPEx1aLNbkzjJw5JrUzX8tMbR9AGNg@mail.gmail.com>
Date:   Thu, 10 Mar 2022 21:48:01 +0800
From:   Muchun Song <songmuchun@...edance.com>
To:     Dan Williams <dan.j.williams@...el.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>,
        Xiyu Yang <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>,
        Xiongchun duan <duanxiongchun@...edance.com>,
        Muchun Song <smuchun@...il.com>
Subject: Re: [PATCH v4 2/6] dax: fix cache flush on PMD-mapped pages

On Thu, Mar 10, 2022 at 8:06 AM Dan Williams <dan.j.williams@...el.com> wrote:
>
> 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:

Right. I'll add this into the commit log.

>
> d92576f1167c dax: does not work correctly with virtual aliasing caches
>
> Otherwise, you can add:
>
> Reviewed-by: Dan Williams <dan.j.williams@...el.com>

Thanks.