From: Arnd Bergmann <arnd@arndb.de>
To: Dan Williams <dan.j.williams@intel.com>
Cc: Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
"H. Peter Anvin" <hpa@zytor.com>,
Thomas Gleixner <tglx@linutronix.de>,
Ross Zwisler <ross.zwisler@linux.intel.com>,
Andrew Morton <akpm@linux-foundation.org>,
Juergen Gross <jgross@suse.com>, X86 ML <x86@kernel.org>,
"Kani, Toshimitsu" <toshi.kani@hp.com>,
"linux-nvdimm@lists.01.org" <linux-nvdimm@lists.01.org>,
Luis Rodriguez <mcgrof@suse.com>,
Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Stefan Bader <stefan.bader@canonical.com>,
Andy Lutomirski <luto@amacapital.net>,
linux-mm@kvack.org, geert@linux-m68k.org,
Henrique de Moraes Holschuh <hmh@hmh.eng.br>,
Tejun Heo <tj@kernel.org>, Christoph Hellwig <hch@lst.de>
Subject: Re: [PATCH v2 3/4] arch: introduce memremap()
Date: Mon, 01 Jun 2015 16:29:55 +0200 [thread overview]
Message-ID: <2979323.pqVEGrEfg7@wuerfel> (raw)
In-Reply-To: <CAPcyv4hqQaabcOsOZA9emT5f+UF9GgD-PiYupng4HYwymcvYmQ@mail.gmail.com>
On Saturday 30 May 2015 14:39:48 Dan Williams wrote:
> On Sat, May 30, 2015 at 2:00 PM, Arnd Bergmann <arnd@arndb.de> wrote:
> > On Saturday 30 May 2015, Dan Williams wrote:
> >>
> >> +/*
> >> + * memremap() is "ioremap" for cases where it is known that the resource
> >> + * being mapped does not have i/o side effects and the __iomem
> >> + * annotation is not applicable.
> >> + */
> >> +
> >> +static inline void *memremap(resource_size_t offset, size_t size)
> >> +{
> >> + return (void __force *) ioremap(offset, size);
> >> +}
> >> +
> >> +static inline void *memremap_nocache(resource_size_t offset, size_t size)
> >> +{
> >> + return (void __force *) ioremap_nocache(offset, size);
> >> +}
> >> +
> >> +static inline void *memremap_cache(resource_size_t offset, size_t size)
> >> +{
> >> + return (void __force *) ioremap_cache(offset, size);
> >> +}
> >> +
> >
> > There are architectures on which the result of ioremap is not necessarily
> > a pointer, but instead indicates that the access is to be done through
> > some other indirect access, or require special instructions. I think implementing
> > the memremap() interfaces is generally helpful, but don't rely on the
> > ioremap implementation.
>
> Is it enough to detect the archs where ioremap() does return an
> otherwise usable pointer and set ARCH_HAS_MEMREMAP, in the first take
> of this introduction? Regardless, it seems that drivers should have
> Kconfig dependency checks for archs where ioremap can not be used in
> this manner.
Yes, that should work.
> > Adding both cached an uncached versions is also dangerous, because you
> > typically get either undefined behavior or a system checkstop when a
> > single page is mapped both cached and uncached at the same time. This
> > means that doing memremap() or memremap_nocache() on something that
> > may be part of the linear kernel mapping is a bug, and we should probably
> > check for that here.
>
> Part of the reason for relying on ioremap() was to borrow its internal
> checks to fail attempts that try to remap ranges that are already in
> the kernel linear map. Hmm, that's a guarantee x86 ioremap gives, but
> maybe that's not universal?
I haven't seen that check elsewhere. IIRC what ioremap() guarantees on ARM
is that if there is an existing boot-time mapping (similar to x86 fixmap,
but more commonly used), we use the same flags in the new ioremap and
override the ones that are provided by the caller.
Arnd
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next prev parent reply other threads:[~2015-06-01 14:32 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-05-30 18:59 [PATCH v2 0/4] pmem api, generic ioremap_cache, and memremap Dan Williams
2015-05-30 18:59 ` [PATCH v2 1/4] arch/*/asm/io.h: add ioremap_cache() to all architectures Dan Williams
2015-06-01 22:36 ` Toshi Kani
2015-06-02 8:20 ` Arnd Bergmann
2015-06-02 8:38 ` Geert Uytterhoeven
2015-05-30 18:59 ` [PATCH v2 2/4] devm: fix ioremap_cache() usage Dan Williams
2015-05-30 20:52 ` Arnd Bergmann
2015-05-30 21:16 ` Dan Williams
2015-06-01 14:26 ` Arnd Bergmann
2015-05-30 18:59 ` [PATCH v2 3/4] arch: introduce memremap() Dan Williams
2015-05-30 21:00 ` Arnd Bergmann
2015-05-30 21:39 ` Dan Williams
2015-06-01 14:29 ` Arnd Bergmann [this message]
2015-05-30 18:59 ` [PATCH v2 4/4] arch, x86: cache management apis for persistent memory Dan Williams
2015-06-01 9:19 ` Paul Bolle
2015-06-01 11:39 ` Boaz Harrosh
2015-06-01 11:44 ` Boaz Harrosh
2015-06-01 16:07 ` Dan Williams
2015-06-01 16:22 ` Dan Williams
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