[RFC PATCH 0/2] arm64: Add support for 48-bit Physical Addresses

[Will Deacon]

On Wed, Nov 27, 2013 at 03:33:45PM +0000, Radha Mohan wrote:
> On Wed, Nov 27, 2013 at 4:34 PM, Marc Zyngier <marc.zyngier at arm.com> wrote:
> > [CC-ing the maintainers - seems odd they were not cc-ed the first place]
> >
> > On 27/11/13 07:34, mohun106 at gmail.com wrote:
> >> From: Radha Mohan Chintakuntla <rchintakuntla at cavium.com>
> >>
> >> This patch series provides an implementation of supporting 48-bit
> >> Physical Addresses for ARMv8 platforms. It is the maximum width that
> >> any ARMv8 based processor can support.
> >>
> >> The implementation extends the existing support of 40-bit PA.The kernel
> >> and user space will now be able to access 128TB each. With 4KB page size
> >> the Linux now will be using 4 levels of page tables by making use of
> >> 'pud'. And with 64KB page size the Linux will be using 3 levels of page
> >> tables.
> >>
> >> The code has been tested with LTP.
> >
> > Aside from finding out whether or not this is a useful change, this
> > breaks KVM, more specifically the way kernel pages are mapped into HYP.
> > Also, guests will still be limited to 40-bit IPAs, and the stage-2
> > output range needs to be addressed as well.
> 
> This is useful for platforms (like ours) that will use 48-bit PAs.
> Sooner or later there will
> be such processors.
> And yes, I haven't checked on KVM.

It may well break the ARM SMMU driver without further changes there, too.

Will