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Re: [PATCH 2/8] pdx: introduce function to calculate max PFN based on PDX compression
- To: Julien Grall <julien@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Michal Orzel <michal.orzel@xxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Thu, 12 Jun 2025 14:02:13 +0200
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- Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Anthony PERARD <anthony.perard@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx, Roger Pau Monné <roger.pau@xxxxxxxxxx>
- Delivery-date: Thu, 12 Jun 2025 12:02:26 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 12.06.2025 12:48, Roger Pau Monné wrote:
> 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?
Question goes to Arm folks.
Jan
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