linux-kernel - Re: [PATCH v4 1/4] arm64/mm: generalize PMD_PRESENT

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Message-ID: <b5c8b363-5656-454e-935c-8cec61f9464c@arm.com>
Date: Wed, 8 May 2024 15:13:48 +0530
From: Anshuman Khandual <anshuman.khandual@....com>
To: Ryan Roberts <ryan.roberts@....com>,
 Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>,
 Joey Gouly <joey.gouly@....com>, Ard Biesheuvel <ardb@...nel.org>,
 Mark Rutland <mark.rutland@....com>, David Hildenbrand <david@...hat.com>,
 Peter Xu <peterx@...hat.com>, Mike Rapoport <rppt@...ux.ibm.com>,
 Shivansh Vij <shivanshvij@...look.com>
Cc: linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 1/4] arm64/mm: generalize PMD_PRESENT_INVALID for all
 levels



On 5/3/24 20:15, Ryan Roberts wrote:
> As preparation for the next patch, which frees up the PTE_PROT_NONE
> present pte and swap pte bit, generalize PMD_PRESENT_INVALID to
> PTE_PRESENT_INVALID. This will then be used to mark PROT_NONE ptes (and
> entries at any other level) in the next patch.
> 
> While we're at it, fix up the swap pte format comment to include
> PTE_PRESENT_INVALID. This is not new, it just wasn't previously
> documented.
> 
> Reviewed-by: Catalin Marinas <catalin.marinas@....com>
> Signed-off-by: Ryan Roberts <ryan.roberts@....com>

Reviewed-by: Anshuman Khandual <anshuman.khandual@....com>

> ---
>  arch/arm64/include/asm/pgtable-prot.h |  8 ++++----
>  arch/arm64/include/asm/pgtable.h      | 21 ++++++++++++---------
>  2 files changed, 16 insertions(+), 13 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/pgtable-prot.h b/arch/arm64/include/asm/pgtable-prot.h
> index dd9ee67d1d87..cdbf51eef7a6 100644
> --- a/arch/arm64/include/asm/pgtable-prot.h
> +++ b/arch/arm64/include/asm/pgtable-prot.h
> @@ -21,11 +21,11 @@
>  #define PTE_PROT_NONE		(_AT(pteval_t, 1) << 58) /* only when !PTE_VALID */
>  
>  /*
> - * This bit indicates that the entry is present i.e. pmd_page()
> - * still points to a valid huge page in memory even if the pmd
> - * has been invalidated.
> + * PTE_PRESENT_INVALID=1 & PTE_VALID=0 indicates that the pte's fields should be
> + * interpreted according to the HW layout by SW but any attempted HW access to
> + * the address will result in a fault. pte_present() returns true.
>   */
> -#define PMD_PRESENT_INVALID	(_AT(pteval_t, 1) << 59) /* only when !PMD_SECT_VALID */
> +#define PTE_PRESENT_INVALID	(_AT(pteval_t, 1) << 59) /* only when !PTE_VALID */
>  
>  #define _PROT_DEFAULT		(PTE_TYPE_PAGE | PTE_AF | PTE_SHARED)
>  #define _PROT_SECT_DEFAULT	(PMD_TYPE_SECT | PMD_SECT_AF | PMD_SECT_S)
> diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
> index afdd56d26ad7..7156c940ac4f 100644
> --- a/arch/arm64/include/asm/pgtable.h
> +++ b/arch/arm64/include/asm/pgtable.h
> @@ -132,6 +132,8 @@ static inline pteval_t __phys_to_pte_val(phys_addr_t phys)
>  #define pte_dirty(pte)		(pte_sw_dirty(pte) || pte_hw_dirty(pte))
>  
>  #define pte_valid(pte)		(!!(pte_val(pte) & PTE_VALID))
> +#define pte_present_invalid(pte) \
> +	((pte_val(pte) & (PTE_VALID | PTE_PRESENT_INVALID)) == PTE_PRESENT_INVALID)
>  /*
>   * Execute-only user mappings do not have the PTE_USER bit set. All valid
>   * kernel mappings have the PTE_UXN bit set.
> @@ -261,6 +263,13 @@ static inline pte_t pte_mkpresent(pte_t pte)
>  	return set_pte_bit(pte, __pgprot(PTE_VALID));
>  }
>  
> +static inline pte_t pte_mkinvalid(pte_t pte)
> +{
> +	pte = set_pte_bit(pte, __pgprot(PTE_PRESENT_INVALID));
> +	pte = clear_pte_bit(pte, __pgprot(PTE_VALID));
> +	return pte;
> +}
> +
>  static inline pmd_t pmd_mkcont(pmd_t pmd)
>  {
>  	return __pmd(pmd_val(pmd) | PMD_SECT_CONT);
> @@ -478,7 +487,7 @@ static inline int pmd_protnone(pmd_t pmd)
>  }
>  #endif
>  
> -#define pmd_present_invalid(pmd)     (!!(pmd_val(pmd) & PMD_PRESENT_INVALID))
> +#define pmd_present_invalid(pmd)	pte_present_invalid(pmd_pte(pmd))
>  
>  static inline int pmd_present(pmd_t pmd)
>  {
> @@ -508,14 +517,7 @@ static inline int pmd_trans_huge(pmd_t pmd)
>  #define pmd_mkclean(pmd)	pte_pmd(pte_mkclean(pmd_pte(pmd)))
>  #define pmd_mkdirty(pmd)	pte_pmd(pte_mkdirty(pmd_pte(pmd)))
>  #define pmd_mkyoung(pmd)	pte_pmd(pte_mkyoung(pmd_pte(pmd)))
> -
> -static inline pmd_t pmd_mkinvalid(pmd_t pmd)
> -{
> -	pmd = set_pmd_bit(pmd, __pgprot(PMD_PRESENT_INVALID));
> -	pmd = clear_pmd_bit(pmd, __pgprot(PMD_SECT_VALID));
> -
> -	return pmd;
> -}
> +#define pmd_mkinvalid(pmd)	pte_pmd(pte_mkinvalid(pmd_pte(pmd)))
>  
>  #define pmd_thp_or_huge(pmd)	(pmd_huge(pmd) || pmd_trans_huge(pmd))
>  
> @@ -1251,6 +1253,7 @@ static inline pmd_t pmdp_establish(struct vm_area_struct *vma,
>   *	bits 3-7:	swap type
>   *	bits 8-57:	swap offset
>   *	bit  58:	PTE_PROT_NONE (must be zero)
> + *	bit  59:	PTE_PRESENT_INVALID (must be zero)
>   */
>  #define __SWP_TYPE_SHIFT	3
>  #define __SWP_TYPE_BITS		5