Re: [PATCH] xen/arm: skip holes in physical address space when setting up frametable

["Orzel, Michal" <michal.orzel@xxxxxxx>]

On 21/04/2026 15:30, Oleksii Kurochko wrote:
> Hello Michał,
> 
> On 4/17/26 11:11 AM, Michal Orzel wrote:
>> Refactor setup_frametable_mappings() into init_frametable(), modeled
>> after x86's implementation. Instead of mapping one contiguous frametable
>> covering ram_start to ram_end (including holes), iterate the
>> pdx_group_valid bitmap to allocate and map frametable memory only for
>> valid PDX groups, skipping gaps in the physical address space. At the
>> moment we don't really take into account pdx_group_valid bitmap.
>>
>> This reduces memory consumption on systems with sparse RAM layouts by
>> not allocating frametable entries for non-existent memory regions.
>>
>> A file-local pdx_to_page() override is needed because the generic macro
>> in xen/include/xen/pdx.h does not account for ARM's non-zero
>> frametable_base_pdx.
>>
>> Update the MPU implementation to match the new init_frametable()
>> signature. Since MPU has no virtual address translation (ma == va),
>> hole-skipping is not possible and the frametable remains a single
>> contiguous allocation.
>>
>> Signed-off-by: Michal Orzel<michal.orzel@xxxxxxx>
>> ---
>> We've been using this approach at AMD for a while now. Without this we would 
>> not
>> be able to boot some of our boards that have huge holes in the PA space, so I
>> consider this patch a great improvement.
>>
>> Two things to consider as a follow-up in the future:
>>   - change generic pdx_to_page, page_to_pdx to take into account offset that
>>     on x86 is zero but on other arches it is not. The page list code is
>>     for now unaffected because the offset cancels out,
>>   - use the same on RISCV.
> 
> Do you have such plans to do that for RISC-V?
My plan for this release cycle is to do this for Arm as we can observe great
improvement in space management. Other things that I mentioned I planned for the
future. I don't want to add new things on our plate in this release.

~Michal