From: catalin.marinas@arm.com (Catalin Marinas)
To: linux-arm-kernel@lists.infradead.org
Subject: arm64 ioremap question
Date: Tue, 15 Oct 2013 16:55:08 +0100 [thread overview]
Message-ID: <20131015155508.GD1591@arm.com> (raw)
In-Reply-To: <20131015155216.GD25034@n2100.arm.linux.org.uk>
On Tue, Oct 15, 2013 at 04:52:16PM +0100, Russell King - ARM Linux wrote:
> On Tue, Oct 15, 2013 at 11:20:04AM -0400, Mark Salter wrote:
> > ioremap() has a test to prevent RAM from being remapped:
> >
> > /*
> > * Don't allow RAM to be mapped.
> > */
> > if (WARN_ON(pfn_valid(__phys_to_pfn(phys_addr))))
> > return NULL;
> >
> >
> > Is this really necessary even for reserved pages which are not being
> > used for anything else?
>
> It helps to stop the abuse of using ioremap() on normal memory, which has
> happened soo much in Aarch32 for years. Unfortuantely, bad habbits die
> hard.
>
> "Reserved pages not being used for anything else" are still mapped, and
> still subject to speculative fetches.
Indeed. The architecture does not guarantee the semantics of the
ioremap-returned memory (e.g. Device) as long as there are other aliases
with different memory attributes.
--
Catalin
next prev parent reply other threads:[~2013-10-15 15:55 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-10-15 15:20 arm64 ioremap question Mark Salter
2013-10-15 15:52 ` Russell King - ARM Linux
2013-10-15 15:55 ` Catalin Marinas [this message]
2013-10-15 16:14 ` Lucas Stach
2013-10-15 16:53 ` Russell King - ARM Linux
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