Re: [PATCH v2 1/9] xen/x86: introduce a helper to update memory hotplug end

[Jan Beulich <jbeulich@xxxxxxxx>]

On 08.07.2022 16:54, Wei Chen wrote:
> x86 provides a mem_hotplug variable to maintain the memory hotplug
> end address. We want to move some codes from x86 to common, so that
> it can be reused by other architectures. But not all architectures
> have supported memory hotplug. So in this patch, we introduce this
> helper to replace mem_hotplug direct access in these codes. This
> will give the ability of stubbing this helper to those architectures
> without memory hotplug support.

What remains unclear to me is why Arm can't simply gain the necessary
variable. Sooner or later you'll want to support hotplug there anyway,
I suppose. Mechanically the change is fine. Albeit maybe "top" instead
of "boundary", and maybe also pass "node" even if x86 doesn't need it?

Jan

> Signed-off-by: Wei Chen <wei.chen@xxxxxxx>
> ---
> v1 -> v2:
> 1. Refine the commit message.
> 2. Merge v1 patch#9,10 into one patch. Introduce the new functions
>    in the same patch that this patch will be used first time.
> 3. Fold if ( end > mem_hotplug ) to mem_hotplug_update_boundary,
>    in this case, we can drop mem_hotplug_boundary.
> ---
>  xen/arch/x86/include/asm/mm.h | 6 ++++++
>  xen/arch/x86/srat.c           | 3 +--
>  2 files changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/xen/arch/x86/include/asm/mm.h b/xen/arch/x86/include/asm/mm.h
> index 07b59c982b..b3dfbdb52b 100644
> --- a/xen/arch/x86/include/asm/mm.h
> +++ b/xen/arch/x86/include/asm/mm.h
> @@ -476,6 +476,12 @@ static inline int get_page_and_type(struct page_info 
> *page,
>  
>  extern paddr_t mem_hotplug;
>  
> +static inline void mem_hotplug_update_boundary(paddr_t end)
> +{
> +    if ( end > mem_hotplug )
> +        mem_hotplug = end;
> +}
> +
>  
> /******************************************************************************
>   * With shadow pagetables, the different kinds of address start
>   * to get get confusing.
> diff --git a/xen/arch/x86/srat.c b/xen/arch/x86/srat.c
> index b62a152911..f53431f5e8 100644
> --- a/xen/arch/x86/srat.c
> +++ b/xen/arch/x86/srat.c
> @@ -418,8 +418,7 @@ acpi_numa_memory_affinity_init(const struct 
> acpi_srat_mem_affinity *ma)
>       memblk_nodeid[num_node_memblks] = node;
>       if (ma->flags & ACPI_SRAT_MEM_HOT_PLUGGABLE) {
>               __set_bit(num_node_memblks, memblk_hotplug);
> -             if (end > mem_hotplug)
> -                     mem_hotplug = end;
> +             mem_hotplug_update_boundary(end);
>       }
>       num_node_memblks++;
>  }