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

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Date: Tue, 7 May 2024 13:38:45 +0200
From: David Hildenbrand <david@...hat.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>,
 Anshuman Khandual <anshuman.khandual@....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 03.05.24 16:45, 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>
> ---
>   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 */

Ah, so PTE_VALID == PMD_SECT_VALID. Would that also be a reasonable 
generalization independent of this? (or do we keep it as is because it's 
a HW def?)

Reviewed-by: David Hildenbrand <david@...hat.com>


-- 
Cheers,

David / dhildenb