linux-kernel - Re: [PATCH v12 3/5] arm64: pgtable: Add p*d_page

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Date:   Mon, 4 Jun 2018 19:13:48 +0530
From:   Chintan Pandya <cpandya@...eaurora.org>
To:     Will Deacon <will.deacon@....com>
Cc:     catalin.marinas@....com, mark.rutland@....com,
        akpm@...ux-foundation.org, toshi.kani@....com,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v12 3/5] arm64: pgtable: Add p*d_page_vaddr helper macros



On 6/4/2018 5:43 PM, Will Deacon wrote:
> On Fri, Jun 01, 2018 at 06:09:16PM +0530, Chintan Pandya wrote:
>> Add helper macros to give virtual references to page
>> tables. These will be used while freeing dangling
>> page tables.
>>
>> Signed-off-by: Chintan Pandya <cpandya@...eaurora.org>
>> ---
>>   arch/arm64/include/asm/pgtable.h | 3 +++
>>   1 file changed, 3 insertions(+)
>>
>> diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
>> index 7c4c8f3..ef4047f 100644
>> --- a/arch/arm64/include/asm/pgtable.h
>> +++ b/arch/arm64/include/asm/pgtable.h
>> @@ -580,6 +580,9 @@ static inline phys_addr_t pgd_page_paddr(pgd_t pgd)
>>   
>>   #endif  /* CONFIG_PGTABLE_LEVELS > 3 */
>>   
>> +#define pmd_page_vaddr(pmd) __va(pmd_page_paddr(pmd))
>> +#define pud_page_vaddr(pud) __va(pud_page_paddr(pud))
> 
> Are these actually needed, or do pte_offset_kernel and pmd_offset do the
> job already?
> 

I introduced these macros for consistency across different arch.

Looking at pte_offset_kernel, it seems to use READ_ONCE() which looks
little costly for its intended use (in next patch) where we already have
dereferenced value. Do you still suggest to remove this ?

> Will
> 

Chintan
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