linux-kernel - Re: [PATCH 09/13] mm/powerpc: Redefine pXd_huge() with pXd

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Message-ID: <7b7d6ce1-4a3f-4392-951d-a9bd146c954c@csgroup.eu>
Date: Thu, 14 Mar 2024 08:45:34 +0000
From: Christophe Leroy <christophe.leroy@...roup.eu>
To: "peterx@...hat.com" <peterx@...hat.com>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "linux-mm@...ck.org" <linux-mm@...ck.org>
CC: "linux-arm-kernel@...ts.infradead.org"
	<linux-arm-kernel@...ts.infradead.org>, Matthew Wilcox <willy@...radead.org>,
	"linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>, Andrew
 Morton <akpm@...ux-foundation.org>, "x86@...nel.org" <x86@...nel.org>, Mike
 Rapoport <rppt@...nel.org>, Muchun Song <muchun.song@...ux.dev>,
	"sparclinux@...r.kernel.org" <sparclinux@...r.kernel.org>, Jason Gunthorpe
	<jgg@...dia.com>, Michael Ellerman <mpe@...erman.id.au>, Nicholas Piggin
	<npiggin@...il.com>, Aneesh Kumar K.V <aneesh.kumar@...nel.org>, "Naveen N.
 Rao" <naveen.n.rao@...ux.ibm.com>
Subject: Re: [PATCH 09/13] mm/powerpc: Redefine pXd_huge() with pXd_leaf()



Le 13/03/2024 à 22:47, peterx@...hat.com a écrit :
> From: Peter Xu <peterx@...hat.com>
> 
> PowerPC book3s 4K mostly has the same definition on both, except pXd_huge()
> constantly returns 0 for hash MMUs.  As Michael Ellerman pointed out [1],
> it is safe to check _PAGE_PTE on hash MMUs, as the bit will never be set so
> it will keep returning false.
> 
> As a reference, __p[mu]d_mkhuge() will trigger a BUG_ON trying to create
> such huge mappings for 4K hash MMUs.  Meanwhile, the major powerpc hugetlb
> pgtable walker __find_linux_pte() already used pXd_leaf() to check hugetlb
> mappings.
> 
> The goal should be that we will have one API pXd_leaf() to detect all kinds
> of huge mappings.  AFAICT we need to use the pXd_leaf() impl (rather than
> pXd_huge() ones) to make sure ie. THPs on hash MMU will also return true.

All kinds of huge mappings ?

pXd_leaf() will detect only leaf mappings (like pXd_huge() ). There are 
also huge mappings through hugepd. On powerpc 8xx we have 8M huge pages 
and 512k huge pages. A PGD entry covers 4M so pgd_leaf() won't report 
those huge pages.

> 
> This helps to simplify a follow up patch to drop pXd_huge() treewide.
> 
> NOTE: *_leaf() definition need to be moved before the inclusion of
> asm/book3s/64/pgtable-4k.h, which defines pXd_huge() with it.
> 
> [1] https://lore.kernel.org/r/87v85zo6w7.fsf@mail.lhotse
> 
> Cc: Michael Ellerman <mpe@...erman.id.au>
> Cc: Nicholas Piggin <npiggin@...il.com>
> Cc: Christophe Leroy <christophe.leroy@...roup.eu>
> Cc: "Aneesh Kumar K.V" <aneesh.kumar@...nel.org>
> Cc: "Naveen N. Rao" <naveen.n.rao@...ux.ibm.com>
> Cc: linuxppc-dev@...ts.ozlabs.org
> Signed-off-by: Peter Xu <peterx@...hat.com>
> ---
>   .../include/asm/book3s/64/pgtable-4k.h        | 14 ++--------
>   arch/powerpc/include/asm/book3s/64/pgtable.h  | 27 +++++++++----------
>   2 files changed, 14 insertions(+), 27 deletions(-)
> 
> diff --git a/arch/powerpc/include/asm/book3s/64/pgtable-4k.h b/arch/powerpc/include/asm/book3s/64/pgtable-4k.h
> index 48f21820afe2..92545981bb49 100644
> --- a/arch/powerpc/include/asm/book3s/64/pgtable-4k.h
> +++ b/arch/powerpc/include/asm/book3s/64/pgtable-4k.h
> @@ -8,22 +8,12 @@
>   #ifdef CONFIG_HUGETLB_PAGE
>   static inline int pmd_huge(pmd_t pmd)
>   {
> -	/*
> -	 * leaf pte for huge page
> -	 */
> -	if (radix_enabled())
> -		return !!(pmd_raw(pmd) & cpu_to_be64(_PAGE_PTE));
> -	return 0;
> +	return pmd_leaf(pmd);
>   }
>   
>   static inline int pud_huge(pud_t pud)
>   {
> -	/*
> -	 * leaf pte for huge page
> -	 */
> -	if (radix_enabled())
> -		return !!(pud_raw(pud) & cpu_to_be64(_PAGE_PTE));
> -	return 0;
> +	return pud_leaf(pud);
>   }
>   
>   /*
> diff --git a/arch/powerpc/include/asm/book3s/64/pgtable.h b/arch/powerpc/include/asm/book3s/64/pgtable.h
> index df66dce8306f..fd7180fded75 100644
> --- a/arch/powerpc/include/asm/book3s/64/pgtable.h
> +++ b/arch/powerpc/include/asm/book3s/64/pgtable.h
> @@ -262,6 +262,18 @@ extern unsigned long __kernel_io_end;
>   
>   extern struct page *vmemmap;
>   extern unsigned long pci_io_base;
> +
> +#define pmd_leaf pmd_leaf
> +static inline bool pmd_leaf(pmd_t pmd)
> +{
> +	return !!(pmd_raw(pmd) & cpu_to_be64(_PAGE_PTE));
> +}
> +
> +#define pud_leaf pud_leaf
> +static inline bool pud_leaf(pud_t pud)
> +{
> +	return !!(pud_raw(pud) & cpu_to_be64(_PAGE_PTE));
> +}
>   #endif /* __ASSEMBLY__ */
>   
>   #include <asm/book3s/64/hash.h>
> @@ -1436,20 +1448,5 @@ static inline bool is_pte_rw_upgrade(unsigned long old_val, unsigned long new_va
>   	return false;
>   }
>   
> -/*
> - * Like pmd_huge(), but works regardless of config options
> - */
> -#define pmd_leaf pmd_leaf
> -static inline bool pmd_leaf(pmd_t pmd)
> -{
> -	return !!(pmd_raw(pmd) & cpu_to_be64(_PAGE_PTE));
> -}
> -
> -#define pud_leaf pud_leaf
> -static inline bool pud_leaf(pud_t pud)
> -{
> -	return !!(pud_raw(pud) & cpu_to_be64(_PAGE_PTE));
> -}
> -
>   #endif /* __ASSEMBLY__ */
>   #endif /* _ASM_POWERPC_BOOK3S_64_PGTABLE_H_ */