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

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Message-ID: <CAPcyv4jxw5rP2UoBF5gKW4tWtcKCj6Z0iXqwbWSCNv9TpjRGEQ@mail.gmail.com>
Date:	Fri, 14 Aug 2015 14:05:23 -0700
From:	Dan Williams <dan.j.williams@...el.com>
To:	Ross Zwisler <ross.zwisler@...ux.intel.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, 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.
--
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