linux-kernel - Re: [PATCH v2] nd_blk: add support for "read flush" DSM flag

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Message-ID: <20150820102147.GB19328@arm.com>
Date:	Thu, 20 Aug 2015 11:21:47 +0100
From:	Will Deacon <will.deacon@....com>
To:	Ross Zwisler <ross.zwisler@...ux.intel.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	"Luis R. Rodriguez" <mcgrof@...e.com>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Borislav Petkov <bp@...e.de>, Christoph Hellwig <hch@....de>,
	Christoph Jaeger <cj@...ux.com>,
	Dan Streetman <ddstreet@...e.org>,
	Dan Williams <dan.j.williams@...el.com>,
	Ingo Molnar <mingo@...hat.com>,
	Juergen Gross <jgross@...e.com>, Len Brown <lenb@...nel.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	Thierry Reding <treding@...dia.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Toshi Kani <toshi.kani@...com>,
	Vishal Verma <vishal.l.verma@...el.com>,
	Yalin Wang <Yalin.Wang@...ymobile.com>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
	"linux-nvdimm@...1.01.org" <linux-nvdimm@...1.01.org>,
	"x86@...nel.org" <x86@...nel.org>
Subject: Re: [PATCH v2] nd_blk: add support for "read flush" DSM flag

On Wed, Aug 19, 2015 at 11:48:04PM +0100, Ross Zwisler wrote:
> Add support for the "read flush" _DSM flag, as outlined in the DSM spec:
> 
> http://pmem.io/documents/NVDIMM_DSM_Interface_Example.pdf
> 
> This flag tells the ND BLK driver that it needs to flush the cache lines
> associated with the aperture after the aperture is moved but before any
> new data is read.  This ensures that any stale cache lines from the
> previous contents of the aperture will be discarded from the processor
> cache, and the new data will be read properly from the DIMM.  We know
> that the cache lines are clean and will be discarded without any
> writeback because either a) the previous aperture operation was a read,
> and we never modified the contents of the aperture, or b) the previous
> aperture operation was a write and we must have written back the dirtied
> contents of the aperture to the DIMM before the I/O was completed.

Is this operation expected to be implemented as a destructive invalidation
(i.e. discarding any dirty lines from the cache) or also a writeback of any
dirtylines as part of the invalidation?

If its the former, we might want to give it a scarier name to ensure that
it doesn't grow users outside of NVDIMM scenarios, since "flush" is used
elsewhere for things like flush_dcache_page.

Will
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