linux-kernel - Re: [RFC PATCH v3 03/16] mm: Provide mm_struct and address to huge_ptep

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Message-ID: <ZlRsMCvVo9tSEFQV@localhost.localdomain>
Date: Mon, 27 May 2024 13:19:12 +0200
From: Oscar Salvador <osalvador@...e.de>
To: Christophe Leroy <christophe.leroy@...roup.eu>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
	Jason Gunthorpe <jgg@...dia.com>, Peter Xu <peterx@...hat.com>,
	Michael Ellerman <mpe@...erman.id.au>,
	Nicholas Piggin <npiggin@...il.com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [RFC PATCH v3 03/16] mm: Provide mm_struct and address to
 huge_ptep_get()

On Sun, May 26, 2024 at 11:22:23AM +0200, Christophe Leroy wrote:
> On powerpc 8xx huge_ptep_get() will need to know whether the given
> ptep is a PTE entry or a PMD entry. This cannot be known with the
> PMD entry itself because there is no easy way to know it from the
> content of the entry.
> 
> So huge_ptep_get() will need to know either the size of the page
> or get the pmd.
> 
> In order to be consistent with huge_ptep_get_and_clear(), give
> mm and address to huge_ptep_get().
> 
> Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
> ---
> v2: Add missing changes in arch implementations
> v3: Fixed a comment in ARM and missing changes in S390
> ---
>  arch/arm/include/asm/hugetlb-3level.h |  4 +--
>  arch/arm64/include/asm/hugetlb.h      |  2 +-
>  arch/arm64/mm/hugetlbpage.c           |  2 +-
>  arch/riscv/include/asm/hugetlb.h      |  2 +-
>  arch/riscv/mm/hugetlbpage.c           |  2 +-
>  arch/s390/include/asm/hugetlb.h       |  4 +--
>  arch/s390/mm/hugetlbpage.c            |  4 +--

I was wondering whether we could do something similar for what we did in
patch#1, so we do not touch architectures code.

  
> diff --git a/mm/gup.c b/mm/gup.c
> index 1611e73b1121..86b5105b82a1 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -2812,7 +2812,7 @@ static int gup_hugepte(pte_t *ptep, unsigned long sz, unsigned long addr,
>  	if (pte_end < end)
>  		end = pte_end;
>  
> -	pte = huge_ptep_get(ptep);
> +	pte = huge_ptep_get(NULL, addr, ptep);

I know that after this series all this code is gone, but I was not sure
about the behaviour between this patch and the last one.

It made me nervous, until I realized that this code is only used
on CONFIG_ARCH_HAS_HUGEPD, which should not be the case anymore for 8xx after
patch#8, and since 8xx is the only one that will use the mm parameter from
huge_ptep_get, we are all good.



-- 
Oscar Salvador
SUSE Labs