From: Toshi Kani <toshi.kani@hpe.com>
To: "Luis R. Rodriguez" <mcgrof@kernel.org>,
"Maciej W. Rozycki" <macro@linux-mips.org>
Cc: Julia Lawall <julia.lawall@lip6.fr>,
Ingo Molnar <mingo@kernel.org>, Toshi Kani <toshi.kani@hp.com>,
Paul McKenney <paulmck@linux.vnet.ibm.com>,
Dave Airlie <airlied@redhat.com>,
Benjamin Herrenschmidt <benh@kernel.crashing.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
linux-arch@vger.kernel.org, X86 ML <x86@kernel.org>,
Daniel Vetter <daniel.vetter@intel.com>,
Thomas Gleixner <tglx@linutronix.de>,
"H. Peter Anvin" <hpa@zytor.com>,
Peter Zijlstra <a.p.zijlstra@chello.nl>,
Borislav Petkov <bp@alien8.de>,
Linus Torvalds <torvalds@linux-foundation.org>,
Andrew Morton <akpm@linux-foundation.org>,
Andy Lutomirski <luto@kernel.org>,
Brian Gerst <brgerst@gmail.com>
Subject: Re: Overlapping ioremap() calls, set_memory_*() semantics
Date: Fri, 15 Apr 2016 08:47:29 -0600 [thread overview]
Message-ID: <1460731649.24985.86.camel@hpe.com> (raw)
In-Reply-To: <20160413211638.GF1990@wotan.suse.de>
On Wed, 2016-04-13 at 23:16 +0200, Luis R. Rodriguez wrote:
> On Thu, Mar 17, 2016 at 04:44:53PM -0600, Toshi Kani wrote:
> > On Wed, 2016-03-16 at 02:45 +0100, Luis R. Rodriguez wrote:
> > > On Fri, Mar 11, 2016 at 03:13:52PM -0700, Toshi Kani wrote:
:
> > >
> > > If aliasing with different cache attributes is not allowed for x86
> > > and if its also rare for other architectures that just leaves the
> > > hunt for valid aliasing uses. That still may be hard to hunt for, but
> > > I also suspect it may be rare.
> >
> > Yes, I'd fail the different cache attribute case if we are to place
> > more strict check.
>
> OK it seems this is a good starting point. How can we get a general
> architecture consensus aliasing with different cache attributes is a
> terrible idea ? Perhaps a patch to WARN/error out and let architectures
> opt in to this piece of code?
I expect aliasing with different cache attributes is a bad idea on most
architectures. Given the fact that track_pfn_remap(), track_pfn_insert(),
etc. are only implemented on x86, I suspect that other architectures would
not be able to implement such check easily, though.
On x86, ioremap() and remap_pfn_range() already fail on a conflicting cache
type if it is not allowed by the rule defined in is_new_memtype_allowed().
This exception handling is necessary for remap_pfn_range() called by
/dev/mem, but I do not think it's necessary for ioremap(). I think we can
start from adding a warning message to ioremap().
> > > > > Are there cases where we change the caching attribute of RAM for
> > > > > valid reasons, outside of legacy quirks?
> > > >
> > > > ati_create_page_map() is one example that it gets a RAM page
> > > > by __get_free_page(), and changes it to UC by calling set_memory_uc
> > > > ().
> > >
> > > Should we instead have an API that lets it ask for RAM and of UC
> > > type? That would seem a bit cleaner. BTW do you happen to know *why*
> > > it needs UC RAM types?
> >
> > This RAM page is then shared between graphic card and CPU. I think
> > this is because graphic card cannot snoop the cache.
>
> Was this reason alone sufficient to open such APIs broadly for RAM?
According to commit 75cbade8ea3, such APIs were introduced because drivers
previously had to deal with low-level staff. So, I think we need to keep
them as long as we have such drivers...
Thanks,
-Toshi
next prev parent reply other threads:[~2016-04-15 14:47 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-03-03 21:28 Overlapping ioremap() calls, set_memory_*() semantics Luis R. Rodriguez
2016-03-03 21:28 ` Luis R. Rodriguez
2016-03-04 9:44 ` Ingo Molnar
2016-03-04 18:18 ` Toshi Kani
2016-03-04 18:18 ` Toshi Kani
2016-03-04 18:51 ` Luis R. Rodriguez
2016-03-04 21:39 ` Toshi Kani
2016-03-05 11:42 ` Ingo Molnar
2016-03-05 11:40 ` Ingo Molnar
2016-03-07 17:03 ` Toshi Kani
2016-03-07 17:03 ` Toshi Kani
2016-03-08 12:16 ` Ingo Molnar
2016-03-09 0:29 ` Toshi Kani
2016-03-09 9:15 ` Ingo Molnar
2016-03-11 22:13 ` Toshi Kani
2016-03-16 1:45 ` Luis R. Rodriguez
2016-03-16 1:45 ` Luis R. Rodriguez
2016-03-17 22:44 ` Toshi Kani
2016-04-13 21:16 ` Luis R. Rodriguez
2016-04-15 14:47 ` Toshi Kani [this message]
2016-04-15 14:47 ` Toshi Kani
2016-04-16 9:20 ` Ingo Molnar
2016-04-16 9:20 ` Ingo Molnar
2016-03-21 17:38 ` Maciej W. Rozycki
2016-04-13 21:03 ` Luis R. Rodriguez
2016-03-11 6:47 ` Andy Lutomirski
2016-03-11 22:36 ` Toshi Kani
2016-03-13 1:02 ` Andy Lutomirski
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