linux-kernel - Re: [PATCH v2 1/3] arm64/mm: Refactor PMD_PRESENT_INVALID and PTE_PROT

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Message-ID: <3a1669be-2cf4-486c-901a-3350cf7ffd25@arm.com>
Date: Tue, 30 Apr 2024 14:34:07 +0100
From: Ryan Roberts <ryan.roberts@....com>
To: Catalin Marinas <catalin.marinas@....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 v2 1/3] arm64/mm: Refactor PMD_PRESENT_INVALID and
 PTE_PROT_NONE bits

On 30/04/2024 14:28, Catalin Marinas wrote:
> On Tue, Apr 30, 2024 at 12:35:49PM +0100, Ryan Roberts wrote:
>> There is still one problem I need to resolve; During this work I discovered that
>> core-mm can call pmd_mkinvalid() for swap pmds. On arm64 this will turn the swap
>> pmd into a present pmd, and BadThings can happen in GUP-fast (and any other
>> lockless SW table walkers). My original fix modified core-mm to only call
>> pmd_mkinvalid() for present pmds. But discussion over there has shown that arm64
>> is the only arch that cannot handle this. So I've been convinced that it's
>> probably more robust to make arm64 handle it gracefully and add tests to
>> debug_vm_pgtable.c to check for this. Patch incoming shortly, but it will cause
>> a conflict with this series. So I'll send a v2 of this once that fix is accepted.
> 
> Sounds fine. I can queue the arm64 pmd_mkinvalid() fix for 6.9 and you
> can base this series on top. But I have a preference for this patchset
> to sit in -next for a bit anyway, so it might be 6.11 material.

Yeah that works for me. I just sent the pmd_mkinvalid() fix.