Re: [PATCH] Revert "mm/pgtable: add stubs for {pmd/pub}_{set/clear}_huge"

From: Christophe Leroy <christophe.leroy@csgroup.eu>
To: Jonathan Marek <jonathan@marek.ca>
Cc: Borislav Petkov <bp@alien8.de>, Ingo Molnar <mingo@redhat.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Peter Zijlstra <peterz@infradead.org>,
	Andy Lutomirski <luto@kernel.org>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Will Deacon <will@kernel.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH] Revert "mm/pgtable: add stubs for {pmd/pub}_{set/clear}_huge"
Date: Sat, 17 Jul 2021 18:31:08 +0200	[thread overview]
Message-ID: <20210717183108.Horde.NxzyIKsItUWF4WlYgwgptg1@messagerie.c-s.fr> (raw)
In-Reply-To: <20210717160118.9855-1-jonathan@marek.ca>

Jonathan Marek <jonathan@marek.ca> a écrit :

> c742199a breaks arm64 for some configs because it stubs out functions which
> should not have been stubbed out.
>
> With 4K pages and ARM64_VA_BITS_39=y, the kernel crashes early on unmapped
> 1G pages in the linear map caused by pud_set_huge() in alloc_init_pud()
> being stubbed out. Reverting c742199a fixes the crash.

This patch is there for a reason. Reverting it will break some other config.

The fix needs to allow it work with all platforms.

I don't understand, why does arm64 needs these PUD helpers when it  
defines __PAGETABLE_PUD_FOLDED ?

Maybe the fix should simply be to ifdef on __PAGETABLE_PUD_FOLDED  
instead of using CONFIG_PGTABLE_LEVELS ?

Thanks
Christophe

>
> Fixes: c742199a ("mm/pgtable: add stubs for {pmd/pub}_{set/clear}_huge")
> Signed-off-by: Jonathan Marek <jonathan@marek.ca>
> ---
>  arch/arm64/mm/mmu.c     | 20 ++++++++------------
>  arch/x86/mm/pgtable.c   | 34 +++++++++++++++-------------------
>  include/linux/pgtable.h | 26 +-------------------------
>  3 files changed, 24 insertions(+), 56 deletions(-)
>
> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
> index d745865084488..9ff0de1b2b93c 100644
> --- a/arch/arm64/mm/mmu.c
> +++ b/arch/arm64/mm/mmu.c
> @@ -1339,7 +1339,6 @@ void *__init fixmap_remap_fdt(phys_addr_t  
> dt_phys, int *size, pgprot_t prot)
>  	return dt_virt;
>  }
>
> -#if CONFIG_PGTABLE_LEVELS > 3
>  int pud_set_huge(pud_t *pudp, phys_addr_t phys, pgprot_t prot)
>  {
>  	pud_t new_pud = pfn_pud(__phys_to_pfn(phys), mk_pud_sect_prot(prot));
> @@ -1354,16 +1353,6 @@ int pud_set_huge(pud_t *pudp, phys_addr_t  
> phys, pgprot_t prot)
>  	return 1;
>  }
>
> -int pud_clear_huge(pud_t *pudp)
> -{
> -	if (!pud_sect(READ_ONCE(*pudp)))
> -		return 0;
> -	pud_clear(pudp);
> -	return 1;
> -}
> -#endif
> -
> -#if CONFIG_PGTABLE_LEVELS > 2
>  int pmd_set_huge(pmd_t *pmdp, phys_addr_t phys, pgprot_t prot)
>  {
>  	pmd_t new_pmd = pfn_pmd(__phys_to_pfn(phys), mk_pmd_sect_prot(prot));
> @@ -1378,6 +1367,14 @@ int pmd_set_huge(pmd_t *pmdp, phys_addr_t  
> phys, pgprot_t prot)
>  	return 1;
>  }
>
> +int pud_clear_huge(pud_t *pudp)
> +{
> +	if (!pud_sect(READ_ONCE(*pudp)))
> +		return 0;
> +	pud_clear(pudp);
> +	return 1;
> +}
> +
>  int pmd_clear_huge(pmd_t *pmdp)
>  {
>  	if (!pmd_sect(READ_ONCE(*pmdp)))
> @@ -1385,7 +1382,6 @@ int pmd_clear_huge(pmd_t *pmdp)
>  	pmd_clear(pmdp);
>  	return 1;
>  }
> -#endif
>
>  int pmd_free_pte_page(pmd_t *pmdp, unsigned long addr)
>  {
> diff --git a/arch/x86/mm/pgtable.c b/arch/x86/mm/pgtable.c
> index 3364fe62b9037..3481b35cb4ec7 100644
> --- a/arch/x86/mm/pgtable.c
> +++ b/arch/x86/mm/pgtable.c
> @@ -682,7 +682,6 @@ int p4d_clear_huge(p4d_t *p4d)
>  }
>  #endif
>
> -#if CONFIG_PGTABLE_LEVELS > 3
>  /**
>   * pud_set_huge - setup kernel PUD mapping
>   *
> @@ -721,23 +720,6 @@ int pud_set_huge(pud_t *pud, phys_addr_t addr,  
> pgprot_t prot)
>  	return 1;
>  }
>
> -/**
> - * pud_clear_huge - clear kernel PUD mapping when it is set
> - *
> - * Returns 1 on success and 0 on failure (no PUD map is found).
> - */
> -int pud_clear_huge(pud_t *pud)
> -{
> -	if (pud_large(*pud)) {
> -		pud_clear(pud);
> -		return 1;
> -	}
> -
> -	return 0;
> -}
> -#endif
> -
> -#if CONFIG_PGTABLE_LEVELS > 2
>  /**
>   * pmd_set_huge - setup kernel PMD mapping
>   *
> @@ -768,6 +750,21 @@ int pmd_set_huge(pmd_t *pmd, phys_addr_t addr,  
> pgprot_t prot)
>  	return 1;
>  }
>
> +/**
> + * pud_clear_huge - clear kernel PUD mapping when it is set
> + *
> + * Returns 1 on success and 0 on failure (no PUD map is found).
> + */
> +int pud_clear_huge(pud_t *pud)
> +{
> +	if (pud_large(*pud)) {
> +		pud_clear(pud);
> +		return 1;
> +	}
> +
> +	return 0;
> +}
> +
>  /**
>   * pmd_clear_huge - clear kernel PMD mapping when it is set
>   *
> @@ -782,7 +779,6 @@ int pmd_clear_huge(pmd_t *pmd)
>
>  	return 0;
>  }
> -#endif
>
>  #ifdef CONFIG_X86_64
>  /**
> diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
> index d147480cdefc7..e24d2c992b112 100644
> --- a/include/linux/pgtable.h
> +++ b/include/linux/pgtable.h
> @@ -1397,34 +1397,10 @@ static inline int p4d_clear_huge(p4d_t *p4d)
>  }
>  #endif /* !__PAGETABLE_P4D_FOLDED */
>
> -#ifndef __PAGETABLE_PUD_FOLDED
>  int pud_set_huge(pud_t *pud, phys_addr_t addr, pgprot_t prot);
> -int pud_clear_huge(pud_t *pud);
> -#else
> -static inline int pud_set_huge(pud_t *pud, phys_addr_t addr, pgprot_t prot)
> -{
> -	return 0;
> -}
> -static inline int pud_clear_huge(pud_t *pud)
> -{
> -	return 0;
> -}
> -#endif /* !__PAGETABLE_PUD_FOLDED */
> -
> -#ifndef __PAGETABLE_PMD_FOLDED
>  int pmd_set_huge(pmd_t *pmd, phys_addr_t addr, pgprot_t prot);
> +int pud_clear_huge(pud_t *pud);
>  int pmd_clear_huge(pmd_t *pmd);
> -#else
> -static inline int pmd_set_huge(pmd_t *pmd, phys_addr_t addr, pgprot_t prot)
> -{
> -	return 0;
> -}
> -static inline int pmd_clear_huge(pmd_t *pmd)
> -{
> -	return 0;
> -}
> -#endif /* !__PAGETABLE_PMD_FOLDED */
> -
>  int p4d_free_pud_page(p4d_t *p4d, unsigned long addr);
>  int pud_free_pmd_page(pud_t *pud, unsigned long addr);
>  int pmd_free_pte_page(pmd_t *pmd, unsigned long addr);
> --
> 2.26.1

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