From: James Bottomley <James.Bottomley@HansenPartnership.com>
To: Paul Mundt <lethal@linux-sh.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>,
FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>,
linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org,
benh@kernel.crashing.org, davem@davemloft.net,
rmk@arm.linux.org.uk
Subject: Re: [RFC PATCH] Update the cachetlb.txt file WRT flush_dcache_page and update_mmu_cache
Date: Mon, 10 May 2010 09:40:08 -0500 [thread overview]
Message-ID: <1273502408.4424.4.camel@mulgrave.site> (raw)
In-Reply-To: <20100510102947.GA14278@linux-sh.org>
On Mon, 2010-05-10 at 19:29 +0900, Paul Mundt wrote:
> On Mon, May 10, 2010 at 11:16:47AM +0100, Catalin Marinas wrote:
> > In most situations, just doing flushing in set_pte_at() would suffice
> > and flush_dcache_page() can be ignored. There are two situations where I
> > still see flush_dcache_page() useful:
> >
> > 1. SMP systems where the cache maintenance operations aren't
> > automatically broadcast in hardware
> > 2. The kernel modifies a page cache page that is already mapped in
> > user space
> >
> > (1) can be worked around on some architectures (though not sure about
> > all of them).
> >
> > Is (2) a valid scenario?
> >
> get_user_pages() ?
Actually, no, not really. get_user_pages() is preparing the pages for
DMA (so it pins and possibly flushes them to make the underlying
physical page in the page cache clean). This means it gathers the
physical pages into a scatter gather list. It actually assumes the
kernel *won't* be touching them (without using kmap), so it doesn't give
the pages an in-kernel mapping.
James
next prev parent reply other threads:[~2010-05-10 14:40 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-05-07 13:24 [RFC PATCH] Update the cachetlb.txt file WRT flush_dcache_page and update_mmu_cache Catalin Marinas
2010-05-10 8:06 ` FUJITA Tomonori
2010-05-10 10:16 ` Catalin Marinas
2010-05-10 10:29 ` Paul Mundt
2010-05-10 14:40 ` James Bottomley [this message]
2010-05-10 14:40 ` James Bottomley
2010-05-10 11:55 ` Matthew Wilcox
2010-05-10 14:00 ` [RFC PATCH] Update the cachetlb.txt file WRT flush_dcache_pageand update_mmu_cache Catalin Marinas
2010-05-10 14:03 ` David Miller
2010-05-10 14:32 ` Catalin Marinas
2010-05-11 11:31 ` [RFC PATCH] Update the cachetlb.txt file WRT flush_dcache_page and update_mmu_cache FUJITA Tomonori
2010-05-11 17:22 ` Catalin Marinas
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