linux-kernel - Re: [PATCH v3 1/5] mm: Define VM

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Message-ID: <87bk17ei8h.fsf@mail.lhotse>
Date: Sun, 01 Sep 2024 21:17:02 +1000
From: Michael Ellerman <mpe@...erman.id.au>
To: Christophe Leroy <christophe.leroy@...roup.eu>, Andrew Morton
 <akpm@...ux-foundation.org>, Steven Rostedt <rostedt@...dmis.org>, Masami
 Hiramatsu <mhiramat@...nel.org>, Mathieu Desnoyers
 <mathieu.desnoyers@...icios.com>, Nicholas Piggin <npiggin@...il.com>,
 Naveen N Rao <naveen@...nel.org>, Nathan Chancellor <nathan@...nel.org>,
 Nick Desaulniers <ndesaulniers@...gle.com>, Bill Wendling
 <morbo@...gle.com>, Justin Stitt <justinstitt@...gle.com>, Shuah Khan
 <shuah@...nel.org>, "Jason A . Donenfeld" <Jason@...c4.com>
Cc: Christophe Leroy <christophe.leroy@...roup.eu>,
 linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
 linux-kselftest@...r.kernel.org, llvm@...ts.linux.dev,
 linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
 linux-trace-kernel@...r.kernel.org, Adhemerval Zanella
 <adhemerval.zanella@...aro.org>, Xi Ruoyao <xry111@...111.site>
Subject: Re: [PATCH v3 1/5] mm: Define VM_DROPPABLE for powerpc/32

Christophe Leroy <christophe.leroy@...roup.eu> writes:
> Commit 9651fcedf7b9 ("mm: add MAP_DROPPABLE for designating always
> lazily freeable mappings") only adds VM_DROPPABLE for 64 bits
> architectures.
>
> In order to also use the getrandom vDSO implementation on powerpc/32,
> use VM_ARCH_1 for VM_DROPPABLE on powerpc/32. This is possible because
> VM_ARCH_1 is used for VM_SAO on powerpc and VM_SAO is only for
> powerpc/64.

Also, there can't be any existing users of VM_SAO on 32-bit, because PROT_SAO
(which maps to VM_SAO) is only accepted on CPUs that support SAO, and
those CPUs are all 64-bit.

cheers