linux-kernel - Re: [PATCH 0/2] Fix BTT data corruptions after crash

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Message-ID: <CAPcyv4hsa-DCYO-YxMCKat5y-dDvGMMgJ5D-cib2TjhyNan4NA@mail.gmail.com>
Date:	Sat, 30 Jan 2016 09:44:17 -0800
From:	Dan Williams <dan.j.williams@...el.com>
To:	Toshi Kani <toshi.kani@....com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, Borislav Petkov <bp@...e.de>,
	Ross Zwisler <ross.zwisler@...ux.intel.com>,
	Vishal L Verma <vishal.l.verma@...el.com>,
	micah.parrish@....com, brian.boylston@....com,
	X86 ML <x86@...nel.org>,
	"linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/2] Fix BTT data corruptions after crash

On Thu, Jan 28, 2016 at 12:43 PM, Toshi Kani <toshi.kani@....com> wrote:
> On Thu, 2016-01-28 at 12:12 -0800, Dan Williams wrote:
[..]
>> I'm wondering if we should just document that this routine does not
>> support unaligned transfers?  Maybe backed by a debug mode that does
>> the alignment check.
>
> Yes, I agree.  For this debug mode, do you have something in mind?  Or
> should we add a new CONFIG option like CONFIG_PMEM_DEBUG?
>

I hesitated to say yes to this since some simple alignment checks
seems like a thin reason to add a new Kconfig symbol.  However, one
way we can test that memcpy_to_pmem() properly bypasses the cache is
to invalidate the cache contents that it touches.  This would have
caught this bug without needing to do a power cycle test.  In
otherwords in debug mode run an 'invd' loop after the copy.