linux-kernel - Re: [RFC PATCH v3 2/2] arm: kernel: fix pci_mmap_page

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Message-ID: <20150126095757.GB23384@e102568-lin.cambridge.arm.com>
Date:	Mon, 26 Jan 2015 09:57:57 +0000
From:	Lorenzo Pieralisi <lorenzo.pieralisi@....com>
To:	Bjorn Helgaas <bhelgaas@...gle.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Arnd Bergmann <arnd@...db.de>,
	Russell King <linux@....linux.org.uk>,
	LAKML <linux-arm-kernel@...ts.infradead.org>,
	Linux PCI <linux-pci@...r.kernel.org>
Subject: Re: [RFC PATCH v3 2/2] arm: kernel: fix pci_mmap_page_range() offset
 calculation

On Fri, Jan 23, 2015 at 11:59:11PM +0000, Bjorn Helgaas wrote:
> On Thu, Nov 13, 2014 at 11:19:16AM +0000, Lorenzo Pieralisi wrote:
> > The pci_mmap_page_range() API should be written to expect offset
> > values representing PCI memory resource addresses as seen by user
> > space, through the pci_resource_to_user() API.
> > 
> > ARM relies on the standard implementation of pci_resource_to_user()
> > which actually is an identity map and exports to user space
> > PCI memory resources as they are stored in PCI devices resources
> > structures, which represent CPU physical addresses (fixed-up using
> > BUS to CPU address conversions) not PCI bus addresses.
> > 
> > Therefore, on ARM platforms where the mapping between CPU and BUS
> > address is not a 1:1 the current pci_mmap_page_range() implementation is
> > erroneous, in that an additional shift is applied to an already fixed-up
> > offset passed from userspace.
> > 
> > Hence, this patch removes the mem_offset from the pgoff calculation
> > since the offset as passed from user space already represents the CPU
> > physical address corresponding to the resource to be mapped, ie no
> > additional offset should be applied.
> > 
> > Cc: Arnd Bergmann <arnd@...db.de>
> > Cc: Russell King <linux@....linux.org.uk>
> > Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@....com>
> 
> Acked-by: Bjorn Helgaas <bhelgaas@...gle.com>

Thank you, I will ask Russell to merge it.

Lorenzo

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