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Date: Fri, 16 Feb 2024 12:35:03 +0000
From: Catalin Marinas <catalin.marinas@arm.com>
To: Ryan Roberts <ryan.roberts@arm.com>
Cc: Will Deacon <will@kernel.org>, Ard Biesheuvel <ardb@kernel.org>,
	Marc Zyngier <maz@kernel.org>, James Morse <james.morse@arm.com>,
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	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
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	linux-kernel@vger.kernel.org
Subject: Re: [PATCH v6 18/18] arm64/mm: Automatically fold contpte mappings
Message-ID: <Zc9Wd0N03pPY5Nq5@arm.com>
References: <20240215103205.2607016-1-ryan.roberts@arm.com>
 <20240215103205.2607016-19-ryan.roberts@arm.com>
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In-Reply-To: <20240215103205.2607016-19-ryan.roberts@arm.com>

On Thu, Feb 15, 2024 at 10:32:05AM +0000, Ryan Roberts wrote:
> There are situations where a change to a single PTE could cause the
> contpte block in which it resides to become foldable (i.e. could be
> repainted with the contiguous bit). Such situations arise, for example,
> when user space temporarily changes protections, via mprotect, for
> individual pages, such can be the case for certain garbage collectors.
> 
> We would like to detect when such a PTE change occurs. However this can
> be expensive due to the amount of checking required. Therefore only
> perform the checks when an indiviual PTE is modified via mprotect
> (ptep_modify_prot_commit() -> set_pte_at() -> set_ptes(nr=1)) and only
> when we are setting the final PTE in a contpte-aligned block.
> 
> Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>

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