linux-kernel - Re: [PATCH] arm64/mm: Avoid direct referencing page table enties in map

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Message-ID: <20240801113440.GB4476@willie-the-truck>
Date: Thu, 1 Aug 2024 12:34:41 +0100
From: Will Deacon <will@...nel.org>
To: Ryan Roberts <ryan.roberts@....com>
Cc: Anshuman Khandual <anshuman.khandual@....com>,
	linux-arm-kernel@...ts.infradead.org,
	Catalin Marinas <catalin.marinas@....com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] arm64/mm: Avoid direct referencing page table enties in
 map_range()

On Thu, Jul 25, 2024 at 11:36:56AM +0100, Ryan Roberts wrote:
> On 25/07/2024 10:10, Anshuman Khandual wrote:
> > Like else where in arm64 platform, use WRITE_ONCE() in map_range() while
> > creating page table entries. This avoids referencing page table entries
> > directly.
> 
> I could be wrong, but I don't think this code is ever operating on live
> pgtables? So there is never a potential to race with the HW walker and therefore
> no need to guarrantee copy atomicity? As long as the correct barriers are placed
> at the point where you load the pgdir into the TTBRx there should be no problem?
> 
> If my assertion is correct, I don't think there is any need for this change.

Agreed.

Will