Re: [PATCH 2/8] pdx: introduce function to calculate max PFN based on PDX compression

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Thu, Jun 12, 2025 at 11:11:14AM +0200, Jan Beulich wrote:
> On 11.06.2025 19:16, Roger Pau Monne wrote:
> > This is the code already present and used by x86 in setup_max_pdx(), which
> > takes into account the current PDX compression, plus the limitation of the
> > virtual memory layout to return the maximum usable PFN in the system,
> > possibly truncating the input PFN provided by the caller.
> > 
> > This helper will be used by upcoming PDX related changes that introduce a
> > new compression algorithm.
> > 
> > Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
> > ---
> >  xen/arch/x86/setup.c  | 19 ++-----------------
> >  xen/common/pdx.c      | 25 +++++++++++++++++++++++++
> >  xen/include/xen/pdx.h |  8 ++++++++
> >  3 files changed, 35 insertions(+), 17 deletions(-)
> 
> This is all fine for x86, but on Arm you introduce unreachable code, which
> Misra dislikes. Yet then it feels like it's wrong anyway that the function
> isn't used there.

I was also concerned regarding why ARM doesn't have an equivalent
function.  Is the frametable there supposed to cover up to the maximum
physical address?  In which case there's likely no need for any PDX
compression in the first place?

Thanks, Roger.