From: Peter Zijlstra <peterz@infradead.org>
To: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>,
Christian Brauner <brauner@kernel.org>, Jan Kara <jack@suse.cz>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>,
Darren Hart <dvhart@infradead.org>,
Davidlohr Bueso <dave@stgolabs.net>,
Andre Almeida <andrealmeid@igalia.com>,
Andrew Morton <akpm@linux-foundation.org>,
Eric Dumazet <edumazet@google.com>,
Kuniyuki Iwashima <kuniyu@google.com>,
Paolo Abeni <pabeni@redhat.com>,
Willem de Bruijn <willemb@google.com>,
"David S. Miller" <davem@davemloft.net>,
Jakub Kicinski <kuba@kernel.org>, Simon Horman <horms@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
Dave Hansen <dave.hansen@linux.intel.com>,
Madhavan Srinivasan <maddy@linux.ibm.com>,
Michael Ellerman <mpe@ellerman.id.au>,
Nicholas Piggin <npiggin@gmail.com>,
linux-block@vger.kernel.org, linux-fsdevel@vger.kernel.org,
linux-kernel@vger.kernel.org, netdev@vger.kernel.org,
linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH v4 10/10] powerpc/uaccess: Implement masked user access
Date: Thu, 6 Nov 2025 13:35:50 +0100 [thread overview]
Message-ID: <20251106123550.GX4067720@noisy.programming.kicks-ass.net> (raw)
In-Reply-To: <5c80dddf8c7b1e75f08b3f42bddde891d6ea3f64.1762427933.git.christophe.leroy@csgroup.eu>
On Thu, Nov 06, 2025 at 12:31:28PM +0100, Christophe Leroy wrote:
> On 32 bits it is more tricky. In theory user space can go up to
> 0xbfffffff while kernel will usually start at 0xc0000000. So a gap
> needs to be added in-between. Allthough in theory a single 4k page
> would suffice, it is easier and more efficient to enforce a 128k gap
> below kernel, as it simplifies the masking.
Do we have the requirement that the first access of a masked pointer is
within 4k of the initial address?
Suppose the pointer is to an 16k array, and the memcpy happens to like
going backwards. Then a 4k hole just won't do.
next prev parent reply other threads:[~2025-11-06 12:36 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-11-06 11:31 [PATCH v4 00/10] powerpc: Implement masked user access Christophe Leroy
2025-11-06 11:31 ` [PATCH v4 01/10] iter: Avoid barrier_nospec() in copy_from_user_iter() Christophe Leroy
2025-11-06 11:31 ` [PATCH v4 02/10] uaccess: Add speculation barrier to copy_from_user_iter() Christophe Leroy
2025-11-15 15:51 ` Thomas Gleixner
2025-11-17 7:06 ` Christophe Leroy (CS GROUP)
2025-11-06 11:31 ` [PATCH v4 03/10] uaccess: Use masked_user_{read/write}_access_begin when required Christophe Leroy
2025-11-15 15:53 ` Thomas Gleixner
2025-11-17 7:11 ` Christophe Leroy (CS GROUP)
2025-11-06 11:31 ` [PATCH v4 04/10] powerpc/uaccess: Move barrier_nospec() out of allow_read_{from/write}_user() Christophe Leroy
2025-11-06 11:31 ` [PATCH v4 05/10] powerpc/uaccess: Remove unused size and from parameters from allow_access_user() Christophe Leroy
2025-11-06 11:31 ` [PATCH v4 06/10] powerpc/uaccess: Remove {allow/prevent}_{read/write/read_write}_{from/to/}_user() Christophe Leroy
2025-11-06 11:31 ` [PATCH v4 07/10] powerpc/uaccess: Refactor user_{read/write/}_access_begin() Christophe Leroy
2025-11-06 11:31 ` [PATCH v4 08/10] powerpc/32s: Fix segments setup when TASK_SIZE is not a multiple of 256M Christophe Leroy
2025-11-06 11:31 ` [PATCH v4 09/10] powerpc/32: Automatically adapt TASK_SIZE based on constraints Christophe Leroy
2025-11-06 11:31 ` [PATCH v4 10/10] powerpc/uaccess: Implement masked user access Christophe Leroy
2025-11-06 12:35 ` Peter Zijlstra [this message]
2025-11-06 13:42 ` David Laight
2025-11-13 6:10 ` [PATCH v4 00/10] powerpc: " Madhavan Srinivasan
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