linux-kernel - Re: DAX filesystem support on ARMv8

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Message-ID: <CAPcyv4j75cQ4dSqyKGuioyyf0O9r0BG0TjFgv+w=64gLah5z6w@mail.gmail.com>
Date:   Tue, 12 Nov 2019 09:15:18 -0800
From:   Dan Williams <dan.j.williams@...el.com>
To:     Bharat Kumar Gogada <bharatku@...inx.com>
Cc:     "linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "willy@...radead.org" <willy@...radead.org>,
        "viro@...iv.linux.org.uk" <viro@...iv.linux.org.uk>,
        "jack@...e.cz" <jack@...e.cz>
Subject: Re: DAX filesystem support on ARMv8

On Mon, Nov 11, 2019 at 6:12 PM Bharat Kumar Gogada <bharatku@...inx.com> wrote:
>
> Hi All,
>
> As per Documentation/filesystems/dax.txt
>
> The DAX code does not work correctly on architectures which have virtually
> mapped caches such as ARM, MIPS and SPARC.
>
> Can anyone please shed light on dax filesystem issue w.r.t ARM architecture ?

The concern is VIVT caches since the kernel will want to flush pmem
addresses with different virtual addresses than what userspace is
using. As far as I know, ARMv8 has VIPT caches, so should not have an
issue. Willy initially wrote those restrictions, but I am assuming
that the concern was managing the caches in the presence of virtual
aliases.