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Subject: Re: [RFC V2 2/3] arm64/mm: Define arch_get_mappable_range()
To:     Anshuman Khandual <anshuman.khandual@arm.com>, linux-mm@kvack.org,
        akpm@linux-foundation.org
Cc:     linux-arm-kernel@lists.infradead.org, linux-s390@vger.kernel.org,
        linux-kernel@vger.kernel.org,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>,
        Ard Biesheuvel <ardb@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>
References: <1606706992-26656-1-git-send-email-anshuman.khandual@arm.com>
 <1606706992-26656-3-git-send-email-anshuman.khandual@arm.com>
From:   David Hildenbrand <david@redhat.com>
Organization: Red Hat GmbH
Message-ID: <1861413c-fd23-f3e2-14f3-00feec6ff2fb@redhat.com>
Date:   Wed, 2 Dec 2020 10:26:38 +0100
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On 30.11.20 04:29, Anshuman Khandual wrote:
> This overrides arch_get_mappable_range() on arm64 platform which will be
> used with recently added generic framework. It drops inside_linear_region()
> and subsequent check in arch_add_memory() which are no longer required.
> 
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> Cc: Will Deacon <will@kernel.org>
> Cc: Ard Biesheuvel <ardb@kernel.org>
> Cc: Mark Rutland <mark.rutland@arm.com>
> Cc: David Hildenbrand <david@redhat.com>
> Cc: linux-arm-kernel@lists.infradead.org
> Cc: linux-kernel@vger.kernel.org
> Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
> ---
>  arch/arm64/mm/mmu.c | 14 ++++++--------
>  1 file changed, 6 insertions(+), 8 deletions(-)
> 
> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
> index ca692a815731..49ec8f2838f2 100644
> --- a/arch/arm64/mm/mmu.c
> +++ b/arch/arm64/mm/mmu.c
> @@ -1444,16 +1444,19 @@ static void __remove_pgd_mapping(pgd_t *pgdir, unsigned long start, u64 size)
>  	free_empty_tables(start, end, PAGE_OFFSET, PAGE_END);
>  }
>  
> -static bool inside_linear_region(u64 start, u64 size)
> +struct range arch_get_mappable_range(void)
>  {
> +	struct range memhp_range;
> +
>  	/*
>  	 * Linear mapping region is the range [PAGE_OFFSET..(PAGE_END - 1)]
>  	 * accommodating both its ends but excluding PAGE_END. Max physical
>  	 * range which can be mapped inside this linear mapping range, must
>  	 * also be derived from its end points.
>  	 */
> -	return start >= __pa(_PAGE_OFFSET(vabits_actual)) &&
> -	       (start + size - 1) <= __pa(PAGE_END - 1);
> +	memhp_range.start = __pa(_PAGE_OFFSET(vabits_actual));
> +	memhp_range.end =  __pa(PAGE_END - 1);
> +	return memhp_range;
>  }
>  
>  int arch_add_memory(int nid, u64 start, u64 size,
> @@ -1461,11 +1464,6 @@ int arch_add_memory(int nid, u64 start, u64 size,
>  {
>  	int ret, flags = 0;
>  
> -	if (!inside_linear_region(start, size)) {
> -		pr_err("[%llx %llx] is outside linear mapping region\n", start, start + size);
> -		return -EINVAL;
> -	}

As discussed, I think something like a VM_BUG_ON() here might makes
sense, indicating that we require the caller to validate upfront. Same
applies to the s390x variant.

Thanks!

> -
>  	if (rodata_full || debug_pagealloc_enabled())
>  		flags = NO_BLOCK_MAPPINGS | NO_CONT_MAPPINGS;
>  
> 


-- 
Thanks,

David / dhildenb