From: Jon Masters <jcm@jonmasters.org>
To: Bharat Kumar Gogada <bharatku@xilinx.com>,
Matthew Wilcox <willy@infradead.org>,
Dan Williams <dan.j.williams@intel.com>
Cc: "linux-nvdimm@lists.01.org" <linux-nvdimm@lists.01.org>,
"linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"viro@zeniv.linux.org.uk" <viro@zeniv.linux.org.uk>,
"jack@suse.cz" <jack@suse.cz>
Subject: Re: DAX filesystem support on ARMv8
Date: Sun, 1 Dec 2019 13:54:45 -0500 [thread overview]
Message-ID: <e01ee855-cb11-d059-6c46-836283b9e251@jonmasters.org> (raw)
In-Reply-To: <MN2PR02MB6336070627E66ED8AE646BACA5710@MN2PR02MB6336.namprd02.prod.outlook.com>
On 11/14/19 1:54 AM, Bharat Kumar Gogada wrote:
>>
>> On Tue, Nov 12, 2019 at 09:15:18AM -0800, Dan Williams wrote:
>>> On Mon, Nov 11, 2019 at 6:12 PM Bharat Kumar Gogada
>> <bharatku@xilinx.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.
>>
>> The kernel will also access data at different virtual addresses from userspace.
>> So VIVT CPUs will be mmap/read/write incoherent, as well as being flush
>> incoherent.
>
> Thanks a lot Wilcox and Dan for clarification.
> So the above restriction only applies to ARM architectures with VIVT caches and not
> for VIPT caches.
VMSAv8-64 (Armv8) requires that data caches behave as if they were PIPT.
Meaning there is not a situation as described above.
Jon.
--
Computer Architect
prev parent reply other threads:[~2019-12-01 21:58 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-11-12 2:12 DAX filesystem support on ARMv8 Bharat Kumar Gogada
2019-11-12 9:49 ` Jan Kara
2019-11-12 17:15 ` Dan Williams
2019-11-12 22:02 ` Matthew Wilcox
2019-11-14 6:54 ` Bharat Kumar Gogada
2019-12-01 18:54 ` Jon Masters [this message]
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