linux-kernel - Re: [PATCH v1 2/2] arm64/mm: Add uffd write-protect support

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Date: Wed, 24 Apr 2024 17:46:48 +0100
From: Catalin Marinas <catalin.marinas@....com>
To: Ryan Roberts <ryan.roberts@....com>
Cc: 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>,
	David Hildenbrand <david@...hat.com>, Peter Xu <peterx@...hat.com>,
	Mike Rapoport <rppt@...ux.ibm.com>,
	Shivansh Vij <shivanshvij@...look.com>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 2/2] arm64/mm: Add uffd write-protect support

On Wed, Apr 24, 2024 at 12:10:17PM +0100, Ryan Roberts wrote:
> @@ -1248,6 +1302,7 @@ static inline pmd_t pmdp_establish(struct vm_area_struct *vma,
>   * Encode and decode a swap entry:
>   *	bits 0-1:	present (must be zero)
>   *	bits 2:		remember PG_anon_exclusive
> + *	bit  3:		remember uffd-wp state
>   *	bits 4-53:	swap offset
>   *	bit  54:	PTE_PROT_NONE (overlays PTE_UXN) (must be zero)
>   *	bits 55-59:	swap type

Ah, I did not realise we need to free up bit 3 from the swap pte as
well. Though maybe patch 1 is fine as is but for the record, it would be
good to justify the decision to go with PTE_UXN. For this patch:

Reviewed-by: Catalin Marinas <catalin.marinas@....com>