Re: [PATCH v3 6/7] xen: introduce Kconfig ARCH_PAGING_MEMPOOL

[Luca Fancellu <Luca.Fancellu@xxxxxxx>]

Hi Jan,

> On 19 Mar 2025, at 11:35, Jan Beulich <jbeulich@xxxxxxxx> wrote:
> 
> On 18.03.2025 14:05, Oleksii Kurochko wrote:
>> 
>> On 3/17/25 9:07 PM, Luca Fancellu wrote:
>>> From: Penny Zheng<Penny.Zheng@xxxxxxx>
>>> 
>>> ARM MPU system doesn't need to use paging memory pool, as MPU memory
>>> mapping table at most takes only one 4KB page, which is enough to
>>> manage the maximum 255 MPU memory regions, for all EL2 stage 1
>>> translation and EL1 stage 2 translation.
>>> 
>>> Introduce ARCH_PAGING_MEMPOOL Kconfig common symbol, selected for Arm
>>> MMU systems, x86 and RISC-V.
>>> 
>>> Wrap the code inside 'construct_domU' that deal with p2m paging
>>> allocation in a new function 'domain_p2m_set_allocation', protected
>>> by ARCH_PAGING_MEMPOOL, this is done in this way to prevent polluting
>>> the former function with #ifdefs and improve readability
>>> 
>>> Introduce arch_{get,set}_paging_mempool_size stubs for architecture
>>> with !ARCH_PAGING_MEMPOOL.
>>> 
>>> Remove 'struct paging_domain' from Arm 'struct arch_domain' when the
>>> field is not required.
>>> 
>>> Signed-off-by: Penny Zheng<penny.zheng@xxxxxxx>
>>> Signed-off-by: Wei Chen<wei.chen@xxxxxxx>
>>> Signed-off-by: Luca Fancellu<luca.fancellu@xxxxxxx>
>>> ---
>>> v3 changes:
>>>  - Introduced ARCH_PAGING_MEMPOOL instead of HAS_PAGING_MEMPOOL
>>> v2 changes:
>>>  - make Kconfig HAS_PAGING_MEMPOOL common
>>>  - protect also "xen,domain-p2m-mem-mb" reading with HAS_PAGING_MEMPOOL
>>>  - do not define p2m_teardown{_allocation} in this patch
>>>  - change commit message
>>> ---
>>>  xen/arch/arm/Kconfig              |  1 +
>>>  xen/arch/arm/dom0less-build.c     | 74 ++++++++++++++++++++-----------
>>>  xen/arch/arm/include/asm/domain.h |  2 +
>>>  xen/arch/riscv/Kconfig            |  1 +
>>>  xen/arch/x86/Kconfig              |  1 +
>>>  xen/common/Kconfig                |  3 ++
>>>  xen/include/xen/domain.h          | 17 +++++++
>>>  7 files changed, 73 insertions(+), 26 deletions(-)
>> 
>> For RISC-V:
>>  Reviewed-by: Oleksii Kurochko<oleksii.kurochko@xxxxxxxxx>
> 
> Mind me asking then why RISC-V needs this at this point? The stubs surely
> were added to address some build issue, not because they are actively
> meaningful?

sorry I’m not a RISC-V expert, I saw the stub and I thought the architecture 
wanted to have them implemented.

If not, is it possible to let the RISC-V people handle that separately? I’ll be 
off until 31st of March and this patch is
useful for Ayan to introduce a building status for arm32.

Cheers,
Luca

> 
> Jan