linux-kernel - Re: [PATCH v2] Revert "mm/pgtable: add stubs for {pmd/pub}_{set/clear}

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Message-ID: <87o8at1bk5.fsf@mpe.ellerman.id.au>
Date:   Fri, 23 Jul 2021 22:04:10 +1000
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Will Deacon <will@...nel.org>,
        Christophe Leroy <christophe.leroy@...roup.eu>
Cc:     catalin.marinas@....com, kernel-team@...roid.com,
        Will Deacon <will@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        linuxppc-dev@...ts.ozlabs.org, Mark Rutland <mark.rutland@....com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mike Rapoport <rppt@...nel.org>,
        Ard Biesheuvel <ardb@...nel.org>,
        linux-arm-kernel@...ts.infradead.org,
        Paul Mackerras <paulus@...ba.org>,
        Jonathan Marek <jonathan@...ek.ca>,
        linux-kernel@...r.kernel.org, Marc Zyngier <maz@...nel.org>,
        Nicholas Piggin <npiggin@...il.com>
Subject: Re: [PATCH v2] Revert "mm/pgtable: add stubs for
 {pmd/pub}_{set/clear}_huge"

Will Deacon <will@...nel.org> writes:
> On Wed, 21 Jul 2021 17:02:13 +1000, Michael Ellerman wrote:
>> This reverts commit c742199a014de23ee92055c2473d91fe5561ffdf.
>> 
>> c742199a014d ("mm/pgtable: add stubs for {pmd/pub}_{set/clear}_huge")
>> breaks arm64 in at least two ways for configurations where PUD or PMD
>> folding occur:
>> 
>>   1. We no longer install huge-vmap mappings and silently fall back to
>>      page-granular entries, despite being able to install block entries
>>      at what is effectively the PGD level.
>> 
>> [...]
>
> Thank you Michael! I owe you a beer next time I see you, if we don't go
> extinct before then.

No worries, thanks to Christophe for identifying the solution while on
vacation!

Beers seem a long way off, but hopefully one day :)

cheers