linux-kernel - Re: [PATCH 0/5] powerpc: Implement masked user access

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Message-ID: <aGkPubjld7r6v2vm@gate>
Date: Sat, 5 Jul 2025 06:42:49 -0500
From: Segher Boessenkool <segher@...nel.crashing.org>
To: Christophe Leroy <christophe.leroy@...roup.eu>
Cc: David Laight <david.laight.linux@...il.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Nicholas Piggin <npiggin@...il.com>, Naveen N Rao <naveen@...nel.org>,
        Madhavan Srinivasan <maddy@...ux.ibm.com>,
        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>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-fsdevel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH 0/5] powerpc: Implement masked user access

Hi!

On Sat, Jul 05, 2025 at 12:55:06PM +0200, Christophe Leroy wrote:
> > > For book3s64, GCC only use isel with -mcpu=power9 or -mcpu=power10
> > 
> > I have no idea what "book3s64" means.
> 
> Well that's the name given in Linux kernel to the 64 bits power CPU
> processors.

A fantasy name.  Great.

> > What is "powerpc/32"?  It does not help if you use different names from
> > what everyone else does.
> 
> Again, that's the way it is called in Linux kernel, refer below commits
> subjects:

And another.

> It means everything built with CONFIG_PPC32

Similar names for very dissimilar concepts, even!  Woohoo!

> > > For powerpc/64 we have less constraint than on powerpc32:
> > > - Kernel memory starts at 0xc000000000000000
> > > - User memory stops at 0x0010000000000000
> > 
> > That isn't true, not even if you mean some existing name.  Usually
> > userspace code is mapped at 256MB (0x10000000).  On powerpc64-linux
> > anyway, different default on different ABIs of course :-)
> 
> 0x10000000 is below 0x0010000000000000, isn't it ? So why isn't it true ?

I understood "starts at".  I read cross-eyed maybe, hehe.


Segher