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

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

On 17/03/2025 21:07, 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(-)
> 
> diff --git a/xen/arch/arm/Kconfig b/xen/arch/arm/Kconfig
> index 5ac6ec0212d2..a4af0b85f158 100644
> --- a/xen/arch/arm/Kconfig
> +++ b/xen/arch/arm/Kconfig
> @@ -75,6 +75,7 @@ choice
> 
>  config MMU
>         bool "MMU"
> +       select ARCH_PAGING_MEMPOOL
>         select HAS_LLC_COLORING if !NUMA && ARM_64
>         select HAS_PMAP
>         select HAS_VMAP
> diff --git a/xen/arch/arm/dom0less-build.c b/xen/arch/arm/dom0less-build.c
> index 573b0d25ae41..6eef6ba91444 100644
> --- a/xen/arch/arm/dom0less-build.c
> +++ b/xen/arch/arm/dom0less-build.c
> @@ -673,21 +673,6 @@ static int __init prepare_dtb_domU(struct domain *d, struct kernel_info *kinfo)
>      return -EINVAL;
>  }
> 
> -static unsigned long __init domain_p2m_pages(unsigned long maxmem_kb,
> -                                             unsigned int smp_cpus)
> -{
> -    /*
> -     * Keep in sync with libxl__get_required_paging_memory().
> -     * 256 pages (1MB) per vcpu, plus 1 page per MiB of RAM for the P2M map,
> -     * plus 128 pages to cover extended regions.
> -     */
> -    unsigned long memkb = 4 * (256 * smp_cpus + (maxmem_kb / 1024) + 128);
> -
> -    BUILD_BUG_ON(PAGE_SIZE != SZ_4K);
> -
> -    return DIV_ROUND_UP(memkb, 1024) << (20 - PAGE_SHIFT);
> -}
> -
>  static int __init alloc_xenstore_evtchn(struct domain *d)
>  {
>      evtchn_alloc_unbound_t alloc;
> @@ -841,6 +826,53 @@ static void __init domain_vcpu_affinity(struct domain *d,
>      }
>  }
> 
> +#ifdef CONFIG_ARCH_PAGING_MEMPOOL
> +
NIT: here and elsewhere. We don't usually separate code from #idef/#else/#endif
with empty lines.

For Arm:
Reviewed-by: Michal Orzel <michal.orzel@amd.com>

~Michal