linux-kernel - Re: [RFC][PATCH 1/4] arm64: Drop alloc function from create

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Date:	Tue, 26 Jan 2016 13:26:02 -0800
From:	Laura Abbott <labbott@...hat.com>
To:	Mark Rutland <mark.rutland@....com>,
	Laura Abbott <labbott@...oraproject.org>
Cc:	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	Ard Biesheuvel <ard.biesheuvel@...aro.org>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCH 1/4] arm64: Drop alloc function from create_mapping

On 01/26/2016 03:22 AM, Mark Rutland wrote:
> On Mon, Jan 25, 2016 at 08:52:12AM -0800, Laura Abbott wrote:
>> create_mapping is only used in fixmap_remap_fdt. All the create_mapping
>> calls need to happen on existing translation table pages without
>> additional allocations. Rather than have an alloc function be called
>> and fail, just set it to NULL and catch it's use.
>
> This looks sensible to me, though I think we should rename
> create_mapping to something that makes it clear that not allocating
> pages is a deliberate design decision, and thus it must be called with
> care.
>
> Perhaps create_mapping_noalloc?

I was wondering about that. That name sounds clearer.

>
> Thanks,
> Mark.
>
>> Signed-off-by: Laura Abbott <labbott@...oraproject.org>
>> ---
>>   arch/arm64/mm/mmu.c | 14 ++++++++++----
>>   1 file changed, 10 insertions(+), 4 deletions(-)
>>
>> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
>> index e141762..2d6e7cf 100644
>> --- a/arch/arm64/mm/mmu.c
>> +++ b/arch/arm64/mm/mmu.c
>> @@ -116,7 +116,9 @@ static void alloc_init_pte(pmd_t *pmd, unsigned long addr,
>>   	pte_t *pte;
>>
>>   	if (pmd_none(*pmd) || pmd_sect(*pmd)) {
>> -		phys_addr_t pte_phys = pgtable_alloc();
>> +		phys_addr_t pte_phys;
>> +		BUG_ON(!pgtable_alloc);
>> +		pte_phys = pgtable_alloc();
>>   		pte = pte_fixmap(pte_phys);
>>   		if (pmd_sect(*pmd))
>>   			split_pmd(pmd, pte);
>> @@ -158,7 +160,9 @@ static void alloc_init_pmd(pud_t *pud, unsigned long addr, unsigned long end,
>>   	 * Check for initial section mappings in the pgd/pud and remove them.
>>   	 */
>>   	if (pud_none(*pud) || pud_sect(*pud)) {
>> -		phys_addr_t pmd_phys = pgtable_alloc();
>> +		phys_addr_t pmd_phys;
>> +		BUG_ON(!pgtable_alloc);
>> +		pmd_phys = pgtable_alloc();
>>   		pmd = pmd_fixmap(pmd_phys);
>>   		if (pud_sect(*pud)) {
>>   			/*
>> @@ -223,7 +227,9 @@ static void alloc_init_pud(pgd_t *pgd, unsigned long addr, unsigned long end,
>>   	unsigned long next;
>>
>>   	if (pgd_none(*pgd)) {
>> -		phys_addr_t pud_phys = pgtable_alloc();
>> +		phys_addr_t pud_phys;
>> +		BUG_ON(!pgtable_alloc);
>> +		pud_phys = pgtable_alloc();
>>   		__pgd_populate(pgd, pud_phys, PUD_TYPE_TABLE);
>>   	}
>>   	BUG_ON(pgd_bad(*pgd));
>> @@ -319,7 +325,7 @@ static void __init create_mapping(phys_addr_t phys, unsigned long virt,
>>   		return;
>>   	}
>>   	__create_pgd_mapping(init_mm.pgd, phys, virt, size, prot,
>> -			     early_pgtable_alloc);
>> +			     NULL);
>>   }
>>
>>   void __init create_pgd_mapping(struct mm_struct *mm, phys_addr_t phys,
>> --
>> 2.5.0
>>