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

[Jan Beulich <jbeulich@suse.com>]

On 19.03.2025 17:31, Oleksii Kurochko wrote:
> 
> On 3/19/25 12:35 PM, Jan Beulich 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@arm.com>
>>>>
>>>> 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@arm.com>
>>>> Signed-off-by: Wei Chen<wei.chen@arm.com>
>>>> Signed-off-by: Luca Fancellu<luca.fancellu@arm.com>
>>>> ---
>>>> 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@gmail.com>
>> 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?
> 
> Only because we have stubs and not to have redefinition compilation 
> error. And, yes, they are not actively meaningful now, at least. I am 
> okay with not enabling of this config for RISC-V but then seems to me we 
> have to drop stubs in riscv/stubs.c. ~ Oleksii

Well, I don't think it's "have to", but I agree that dropping them would
make sense then (and be desirable).

Jan