linux-kernel - Re: [PATCH 2/2] arm64/mm: Use CONT_SHIFT to define CONT_PTE

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Message-ID: <966505a6-16f6-8129-804b-fcf890429fb8@arm.com>
Date:   Thu, 10 Sep 2020 14:58:22 +0530
From:   Anshuman Khandual <anshuman.khandual@....com>
To:     Gavin Shan <gshan@...hat.com>, linux-arm-kernel@...ts.infradead.org
Cc:     linux-kernel@...r.kernel.org, catalin.marinas@....com,
        will@...nel.org, shan.gavin@...il.com
Subject: Re: [PATCH 2/2] arm64/mm: Use CONT_SHIFT to define CONT_PTE_SHIFT



On 09/10/2020 02:01 PM, Gavin Shan wrote:
> Hi Anshuman,
> 
> On 9/10/20 4:17 PM, Anshuman Khandual wrote:
>> On 09/08/2020 12:49 PM, Gavin Shan wrote:
>>> The macro CONT_PTE_SHIFT actually depends on CONT_SHIFT, which has
>>> been defined in page-def.h, based on CONFIG_ARM64_CONT_SHIFT. Lets
>>> reflect the dependency.
>>>
>>> Signed-off-by: Gavin Shan <gshan@...hat.com>
>>> ---
>>>   arch/arm64/include/asm/pgtable-hwdef.h | 4 +---
>>>   1 file changed, 1 insertion(+), 3 deletions(-)
>>>
>>> diff --git a/arch/arm64/include/asm/pgtable-hwdef.h b/arch/arm64/include/asm/pgtable-hwdef.h
>>> index 8a399e666837..0bd9469f4323 100644
>>> --- a/arch/arm64/include/asm/pgtable-hwdef.h
>>> +++ b/arch/arm64/include/asm/pgtable-hwdef.h
>>> @@ -81,14 +81,12 @@
>>>   /*
>>>    * Contiguous page definitions.
>>>    */
>>> +#define CONT_PTE_SHIFT        (CONT_SHIFT + PAGE_SHIFT)
>>>   #ifdef CONFIG_ARM64_64K_PAGES
>>> -#define CONT_PTE_SHIFT        (5 + PAGE_SHIFT)
>>>   #define CONT_PMD_SHIFT        (5 + PMD_SHIFT)
>>>   #elif defined(CONFIG_ARM64_16K_PAGES)
>>> -#define CONT_PTE_SHIFT        (7 + PAGE_SHIFT)
>>>   #define CONT_PMD_SHIFT        (5 + PMD_SHIFT)
>>>   #else
>>> -#define CONT_PTE_SHIFT        (4 + PAGE_SHIFT)
>>>   #define CONT_PMD_SHIFT        (4 + PMD_SHIFT)
>>>   #endif
>> Could not a similar CONT_PMD be created from a new CONFIG_ARM64_CONT_PMD
>> config option, which would help unify CONT_PMD_SHIFT here as well ?
>>
> 
> I was thinking of it, to have CONFIG_ARM64_CONT_PMD and defined the
> following macros in arch/arm64/include/asm/page-def.h:
> 
>    #define CONT_PMD_SHIFT    CONFIG_ARM64_CONT_PMD_SHIFT
>    #define CONT_PMD_SIZE        (_AC(1, UL) << (CONT_PMD_SHIFT + PMD_SHIFT)
>    #define CONT_PMD_MASK        (~(CONT_PMD_SIZE - 1))
> 
> PMD_SHIFT is variable because PMD could be folded into PUD or PGD,
> depending on the kernel configuration. PMD_SHIFT is declared

Even CONT_PMD_SHIFT via the new CONFIG_ARM64_CONT_PMD_SHIFT will
be a variable as well depending on page size.

> in arch/arm64/include/asm/pgtable-types.h, which isn't supposed
> to be included in "page-def.h".

Are there build failures if <pgtable-types.h> is included from <page-def.h> ?

> 
> So the peroper way to handle this might be drop the continuous page
> macros in page-def.h and introduce the following ones into pgtable-hwdef.h.
> I will post v2 to do this if it sounds good to you.

Sure, go ahead if that builds. But unifying both these macros seems cleaner.

> 
>    #define CONT_PTE_SHIFT         (CONFIG_ARM64_CONT_PTE_SHIFT + PAGE_SHIFT)
>    #define CONT_PMD_SHIFT         (CONFIG_ARM64_CONT_PMD_SHIFT + PMD_SHIFT)
> 
> Thanks,
> Gavin
> 
>