linux-kernel - Re: [PATCH V2 1/3] mm/hotplug: Prevalidate the address range being added with platform

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Date:   Mon, 11 Jan 2021 11:51:47 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Anshuman Khandual <anshuman.khandual@....com>, linux-mm@...ck.org,
        akpm@...ux-foundation.org, hca@...ux.ibm.com,
        catalin.marinas@....com
Cc:     linux-arm-kernel@...ts.infradead.org, linux-s390@...r.kernel.org,
        linux-kernel@...r.kernel.org, Vasily Gorbik <gor@...ux.ibm.com>,
        Will Deacon <will@...nel.org>,
        Ard Biesheuvel <ardb@...nel.org>,
        Mark Rutland <mark.rutland@....com>
Subject: Re: [PATCH V2 1/3] mm/hotplug: Prevalidate the address range being
 added with platform

On 17.12.20 16:28, Anshuman Khandual wrote:
> This introduces memhp_range_allowed() which can be called in various memory
> hotplug paths to prevalidate the address range which is being added, with
> the platform. Then memhp_range_allowed() calls memhp_get_pluggable_range()
> which provides applicable address range depending on whether linear mapping
> is required or not. For ranges that require linear mapping, it calls a new
> arch callback arch_get_mappable_range() which the platform can override. So
> the new callback, in turn provides the platform an opportunity to configure
> acceptable memory hotplug address ranges in case there are constraints.
> 
> This mechanism will help prevent platform specific errors deep down during
> hotplug calls. This drops now redundant check_hotplug_memory_addressable()
> check in __add_pages() but instead adds a VM_BUG_ON() check which would
> ensure that the range has been validated with memhp_range_allowed() earlier
> in the call chain. Besides memhp_get_pluggable_range() also can be used by
> potential memory hotplug callers to avail the allowed physical range which
> would go through on a given platform.
> 
> This does not really add any new range check in generic memory hotplug but
> instead compensates for lost checks in arch_add_memory() where applicable
> and check_hotplug_memory_addressable(), with unified memhp_range_allowed().
> 

Subject s/mm\/hotplug/mm\/memory_hotplug/

Everywhere in this patch: Use "true/false" for boolean values.

> Cc: David Hildenbrand <david@...hat.com>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: linux-mm@...ck.org
> Cc: linux-kernel@...r.kernel.org
> Suggested-by: David Hildenbrand <david@...hat.com>
> Signed-off-by: Anshuman Khandual <anshuman.khandual@....com>
> ---
>  include/linux/memory_hotplug.h | 10 +++++
>  mm/memory_hotplug.c            | 79 +++++++++++++++++++++++++---------
>  mm/memremap.c                  |  6 +++
>  3 files changed, 75 insertions(+), 20 deletions(-)
> 
> diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h
> index 551093b74596..8d72354758c8 100644
> --- a/include/linux/memory_hotplug.h
> +++ b/include/linux/memory_hotplug.h
> @@ -70,6 +70,9 @@ typedef int __bitwise mhp_t;
>   */
>  #define MEMHP_MERGE_RESOURCE	((__force mhp_t)BIT(0))
>  
> +bool memhp_range_allowed(u64 start, u64 size, bool need_mapping);
> +struct range memhp_get_pluggable_range(bool need_mapping);

AFAIKs, all memhp_get_pluggable_range() users pass "1".

What about the "add_pages()-only" path?

-- 
Thanks,

David / dhildenb