From: Jamie Lokier <jamie@shareable.org>
To: Catalin Marinas <catalin.marinas@arm.com>
Cc: Nick Piggin <npiggin@suse.de>,
Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Ralf Baechle <ralf@linux-mips.org>,
Paul Mackerras <paulus@samba.org>,
linux-arch@vger.kernel.org, Russell King <rmk@arm.linux.org.uk>,
Francois Romieu <romieu@fr.zoreil.com>
Subject: Re: SMP barriers semantics
Date: Sat, 24 Apr 2010 02:45:36 +0100 [thread overview]
Message-ID: <20100424014536.GD15349@shareable.org> (raw)
In-Reply-To: <1272043500.15107.87.camel@e102109-lin.cambridge.arm.com>
Catalin Marinas wrote:
> On recent ARM cores, it's only the Strongly Ordered memory that can have
> the write buffering disabled. But using such mapping for
> dma_alloc_coherent() introduces other problems like cache attribute
> aliases for a physical location (since the kernel maps the RAM as Normal
> memory already). Such aliases are not allowed hence we moved to Normal
> Non-cacheable for dma_alloc_coherent().
I'm surprised aliases between Normal-Cached and Normal-Uncached are ok,
while aliases between Normal-Cached and SO-Uncached are not ok.
Is it theoretically ok by the ARM specs, or just optimistic programming? :-)
If optimism, it's easy to imagine an implementation where
(unrequested) speculative reads populate the cached mapping, and then
accesses to the Normal-Uncached alias of it get a cache hit and use
that, wrongly. Or, conversely, if it definitely does not treat that
as a cache hit, it's hard to imagine why SO-Uncached would be different.
-- Jamie
next prev parent reply other threads:[~2010-04-24 1:45 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-03-02 10:52 SMP barriers semantics Catalin Marinas
2010-03-03 0:55 ` Paul Mackerras
2010-03-03 12:03 ` Catalin Marinas
2010-03-12 12:31 ` Ralf Baechle
2010-03-12 20:38 ` Jamie Lokier
2010-03-17 2:25 ` Benjamin Herrenschmidt
2010-03-17 10:31 ` Catalin Marinas
2010-03-17 13:42 ` Jamie Lokier
2010-03-22 12:02 ` Nick Piggin
2010-03-23 3:42 ` Nick Piggin
2010-03-23 10:24 ` Catalin Marinas
2010-04-06 14:20 ` Nick Piggin
2010-04-06 15:43 ` Jamie Lokier
2010-04-06 16:04 ` Nick Piggin
2010-04-23 16:23 ` Catalin Marinas
2010-04-23 16:56 ` Jamie Lokier
2010-04-23 17:25 ` Catalin Marinas
2010-04-24 1:45 ` Jamie Lokier [this message]
2010-04-26 9:21 ` Catalin Marinas
2010-03-04 2:23 ` David Dillow
2010-03-04 9:33 ` Russell King
2010-03-04 9:48 ` Catalin Marinas
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