linux-kernel - Re: [PATCH v12 01/14] ARM: mm: add missing pud

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Message-Id: <1612321006.e59gckigqu.astroid@bobo.none>
Date:   Wed, 03 Feb 2021 13:01:47 +1000
From:   Nicholas Piggin <npiggin@...il.com>
To:     Russell King - ARM Linux admin <linux@...linux.org.uk>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        Ding Tianhong <dingtianhong@...wei.com>,
        Christoph Hellwig <hch@...radead.org>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        linux-arch@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linuxppc-dev@...ts.ozlabs.org,
        Rick Edgecombe <rick.p.edgecombe@...el.com>
Subject: Re: [PATCH v12 01/14] ARM: mm: add missing pud_page define to 2-level
 page tables

Excerpts from Russell King - ARM Linux admin's message of February 2, 2021 9:13 pm:
> On Tue, Feb 02, 2021 at 09:05:02PM +1000, Nicholas Piggin wrote:
>> diff --git a/arch/arm/include/asm/pgtable.h b/arch/arm/include/asm/pgtable.h
>> index c02f24400369..d63a5bb6bd0c 100644
>> --- a/arch/arm/include/asm/pgtable.h
>> +++ b/arch/arm/include/asm/pgtable.h
>> @@ -166,6 +166,9 @@ extern struct page *empty_zero_page;
>>  
>>  extern pgd_t swapper_pg_dir[PTRS_PER_PGD];
>>  
>> +#define pud_page(pud)		pmd_page(__pmd(pud_val(pud)))
>> +#define pud_write(pud)		pmd_write(__pmd(pud_val(pud)))
> 
> As there is no PUD, does it really make sense to return a valid
> struct page (which will be the PTE page) for pud_page(), which is
> several tables above?

There is no PUD on 3-level either, and the pgtable-nopud.h which it uses 
also passes down p4d_page to pud_page, so by convention...

Although in this case at least for my next patch it won't acutally use 
pud_page unless it's a leaf entry so maybe it shouldn't get called
anyway.

Thanks,
Nick