On Fri, 2017-03-24 at 17:05 +0100, Arnd Bergmann wrote: > On Wed, Mar 22, 2017 at 2:25 PM, David Woodhouse <dwmw2@xxxxxxxxxxxxx> wrote: > > > > From: David Woodhouse <dwmw@xxxxxxxxxxxx> > > > > The /proc/bus/pci mmap interface allows the user to specify whether they > > want WC or not. Don't let them do so on non-prefetchable BARs. > > > > Signed-off-by: David Woodhouse <dwmw@xxxxxxxxxxxx> > > Cc: stable@xxxxxxxxxxxxxxx > Can you explain this a little more? I understand that we usually want to use > WC mappings on prefetchable BARs, and uncached non-WC on > non-prefetchable, but why do we have to force an error here? > > Couldn't there be some hardware that allows write-combining access > but no prefetches? Note that this is only for the procfs interface. The sysfs interface already imposes the same restriction by just *not* creating the 'resourceX_wc' attr when the resource isn't prefetchable. So this just brings procfs into line.
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