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

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Date:	Fri, 14 Aug 2015 15:07:21 -0600
From:	Ross Zwisler <ross.zwisler@...ux.intel.com>
To:	Dan Williams <dan.j.williams@...el.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Christoph Jaeger <cj@...ux.com>,
	Juergen Gross <jgross@...e.com>, X86 ML <x86@...nel.org>,
	Yalin Wang <Yalin.Wang@...ymobile.com>,
	"linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>,
	Will Deacon <will.deacon@....com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Linux ACPI <linux-acpi@...r.kernel.org>,
	Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Russell King <rmk+kernel@....linux.org.uk>,
	Borislav Petkov <bp@...e.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Dan Streetman <ddstreet@...e.org>, Len Brown <lenb@...nel.org>
Subject: Re: [PATCH] nd_blk: add support for "read flush" DSM flag

On Fri, 2015-08-14 at 14:05 -0700, Dan Williams wrote:
> On Fri, Aug 14, 2015 at 1:43 PM, Ross Zwisler
> <ross.zwisler@...ux.intel.com> 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.
> >
> > By supporting the "read flush" flag we can also change the ND BLK
> > aperture mapping from write-combining to write-back via memremap().
> >
> > In order to add support for the "read flush" flag I needed to add a
> > generic routine to invalidate cache lines, mmio_flush_range().  This is
> > protected by the ARCH_HAS_MMIO_FLUSH Kconfig variable, and is currently
> > only supported on x86.
> >
> > Signed-off-by: Ross Zwisler <ross.zwisler@...ux.intel.com>
> > ---
> >  arch/x86/Kconfig                  |  1 +
> >  arch/x86/include/asm/cacheflush.h |  2 ++
> >  drivers/acpi/Kconfig              |  1 +
> >  drivers/acpi/nfit.c               | 55 ++++++++++++++++++++++-----------------
> >  drivers/acpi/nfit.h               | 16 ++++++++----
> >  lib/Kconfig                       |  3 +++
> >  6 files changed, 49 insertions(+), 29 deletions(-)
> >
> [..]
> > diff --git a/drivers/acpi/nfit.c b/drivers/acpi/nfit.c
> > index 628a42c..816c778 100644
> > --- a/drivers/acpi/nfit.c
> > +++ b/drivers/acpi/nfit.c
> [..]
> > @@ -1206,20 +1214,19 @@ static void __iomem *__nfit_spa_map(struct acpi_nfit_desc *acpi_desc,
> >         if (!res)
> >                 goto err_mem;
> >
> > -       if (type == SPA_MAP_APERTURE) {
> > -               /*
> > -                * TODO: memremap_pmem() support, but that requires cache
> > -                * flushing when the aperture is moved.
> > -                */
> > -               spa_map->iomem = ioremap_wc(start, n);
> > -       } else
> > -               spa_map->iomem = ioremap_nocache(start, n);
> > +       spa_map->type = type;
> > +       if (type == SPA_MAP_APERTURE)
> > +               spa_map->addr.aperture = (void __pmem *)memremap(start, n,
> > +                                                               MEMREMAP_WB);
> 
> This should be s/MEMREMAP_WB/ARCH_MEMREMAP_PMEM/, but other than that
> looks good to me.
> 
> I also should go move ARCH_MEMREMAP_PMEM over to
> arch/x86/include/asm/pmem.h and fold it in to your other pending
> pmem-api cleanups.

Sounds good.  Would you like a v2 with those changes, or would you rather
fix it as you apply it to the nvdimm tree?


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