Query: Multiple Mappings to Mem and ARMV6+
catalin.marinas at arm.com
Thu Feb 16 17:29:28 UTC 2012
On Thu, Feb 16, 2012 at 05:22:42PM +0000, Russell King - ARM Linux wrote:
> On Thu, Feb 16, 2012 at 05:15:20PM +0000, Catalin Marinas wrote:
> > On Thu, Feb 16, 2012 at 04:41:02PM +0000, viresh kumar wrote:
> > > Sorry for starting the long old thread again, but i have to start it as i
> > > was a bit confused. :(
> > >
> > > We know that we can't have multiple mappings with different attributes
> > > to the same physical memory on ARMv6+ machines due to speculative
> > > prefetch.
> > >
> > > So, we have following kind of mappings in kernel now (please correct me
> > > if i am wrong):
> > > - Low Mem: Mapped at boot time to - Normal Cacheable - Bufferable
> > > - ioremap() - blocked on Low Mem, so that we don't create Device type mapping
> > > to same mem
> > > - dma_alloc_coherent() and others:
> > > - Without DMA_MEM_BUFFERABLE selected - gives strongly ordered mem
> > > (i.e. Non cacheable - Non Bufferable)
> > > - With DMA_MEM_BUFFERABLE selected - gives Normal - Non cacheable -
> > > Bufferable mapping
> > > - Maybe some other too...
> > >
> > > I have a doubt with the last mapping mentioned above. We have two
> > > mappings possibly to the same physical memory, with different
> > > attributes: One is Cacheable and other one is not.
> > >
> > > Is this allowed by ARM? Because the patch in which Russell blocked
> > > ioremap on Low Mem, he clearly mentioned that these attributes are
> > > also important and they should be same.
> > Section A3.5.7 in the latest ARM ARM (revC) clarifies the mismatched
> There's a new version?
Rev C has been available for a while. I thought you got it already:
It contains the LPAE and virtualisation extensions.
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