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

[Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>]

On 3/26/25 10:39 AM, Orzel, Michal wrote:

> On 20/03/2025 08:32, Jan Beulich wrote:
> > 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@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?
> > > >           
> > > 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, @Oleksii, is there anything blocking this patch to be committed (Luca
> question does not seem to be answered)? Other patches in the series are ready to
> be merged.
>     
I think the change in xen/arch/riscv/Kconfig should be dropped with dropping
arch_{get,set}_paging_mempool_size() in riscv/stubs.c as they are defined in
xen/domain.h for the case when CONFIG_ARCH_PAGING_MEMPOOL=n.

~ Oleksii