linux-kernel - Re: [PATCH 0/2] "big hammer" for DAX msync/fsync correctness

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAPcyv4jYc_Ai+9st_QgzuWNMMHCQ-j6pe4R0XEWy5-mEb1_X5Q@mail.gmail.com>
Date:	Thu, 5 Nov 2015 15:59:46 -0800
From:	Dan Williams <dan.j.williams@...el.com>
To:	Ross Zwisler <ross.zwisler@...ux.intel.com>
Cc:	Jeff Moyer <jmoyer@...hat.com>,
	linux-nvdimm <linux-nvdimm@...1.01.org>, X86 ML <x86@...nel.org>,
	Dave Chinner <david@...morbit.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>, Jan Kara <jack@...e.com>
Subject: Re: [PATCH 0/2] "big hammer" for DAX msync/fsync correctness

On Wed, Oct 28, 2015 at 3:51 PM, Ross Zwisler
<ross.zwisler@...ux.intel.com> wrote:
> On Wed, Oct 28, 2015 at 06:24:29PM -0400, Jeff Moyer wrote:
>> Ross Zwisler <ross.zwisler@...ux.intel.com> writes:
>>
>> > This series implements the very slow but correct handling for
>> > blkdev_issue_flush() with DAX mappings, as discussed here:
>> >
>> > https://lkml.org/lkml/2015/10/26/116
>> >
>> > I don't think that we can actually do the
>> >
>> >     on_each_cpu(sync_cache, ...);
>> >
>> > ...where sync_cache is something like:
>> >
>> >     cache_disable();
>> >     wbinvd();
>> >     pcommit();
>> >     cache_enable();
>> >
>> > solution as proposed by Dan because WBINVD + PCOMMIT doesn't guarantee that
>> > your writes actually make it durably onto the DIMMs.  I believe you really do
>> > need to loop through the cache lines, flush them with CLWB, then fence and
>> > PCOMMIT.
>>
>> *blink*
>> *blink*
>>
>> So much for not violating the principal of least surprise.  I suppose
>> you've asked the hardware folks, and they've sent you down this path?
>
> Sadly, yes, this was the guidance from the hardware folks.

So it turns out we weren't asking the right question.  wbinvd may
indeed be viable... we're still working through the caveats.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/