linux-kernel - Re: [PATCH v4 00/10] powerpc: Implement masked user access

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Message-ID: <20251106135356.51721903@pumpkin>
Date: Thu, 6 Nov 2025 13:53:56 +0000
From: David Laight <david.laight.linux@...il.com>
To: Christophe Leroy <christophe.leroy@...roup.eu>
Cc: Alexander Viro <viro@...iv.linux.org.uk>, Christian Brauner
 <brauner@...nel.org>, Jan Kara <jack@...e.cz>, Thomas Gleixner
 <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Peter Zijlstra
 <peterz@...radead.org>, Darren Hart <dvhart@...radead.org>, Davidlohr Bueso
 <dave@...olabs.net>, "Andre Almeida" <andrealmeid@...lia.com>, Andrew
 Morton <akpm@...ux-foundation.org>, Eric Dumazet <edumazet@...gle.com>,
 Kuniyuki Iwashima <kuniyu@...gle.com>, Paolo Abeni <pabeni@...hat.com>,
 Willem de Bruijn <willemb@...gle.com>, "David S. Miller"
 <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, Simon Horman
 <horms@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, Dave Hansen
 <dave.hansen@...ux.intel.com>, Madhavan Srinivasan <maddy@...ux.ibm.com>,
 Michael Ellerman <mpe@...erman.id.au>, Nicholas Piggin <npiggin@...il.com>,
 linux-kernel@...r.kernel.org, x86@...nel.org
Subject: Re: [PATCH v4 00/10] powerpc: Implement masked user access

On Thu,  6 Nov 2025 12:31:18 +0100
Christophe Leroy <christophe.leroy@...roup.eu> wrote:

> This is a rebase on top of commit 6ec821f050e2 (tag: core-scoped-uaccess)
> from tip tree.
> 
> Thomas, Peter, could you please take non-powerpc patches (1, 2, 3)
> in tip tree for v6.19, then Maddy will take powerpc patches (4-10)
> into powerpc-next for v6.20.
> 
> Masked user access avoids the address/size verification by access_ok().
> Allthough its main purpose is to skip the speculation in the
> verification of user address and size hence avoid the need of spec
> mitigation, it also has the advantage to reduce the amount of
> instructions needed so it also benefits to platforms that don't
> need speculation mitigation, especially when the size of the copy is
> not know at build time.
...

Any thoughts on doing the same changes to 32bit x86?

I think it just requires that TASK_SIZE_MASK be reduced by 4k and
then the address 'mask' code written.

	David