linux-kernel - Re: [PATCH v14 1/4] asm-generic,arm64: create task variant of access

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Message-ID: <20230329235442.GA10790@redhat.com>
Date:   Thu, 30 Mar 2023 01:54:43 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     Gregory Price <gregory.price@...verge.com>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Gregory Price <gourry.memverge@...il.com>,
        linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        Linux-Arch <linux-arch@...r.kernel.org>, avagin@...il.com,
        Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>, krisman@...labora.com,
        Thomas Gleixner <tglx@...utronix.de>,
        Jonathan Corbet <corbet@....net>, shuah <shuah@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Mark Rutland <mark.rutland@....com>, tongtiangen@...wei.com,
        Robin Murphy <robin.murphy@....com>
Subject: Re: [PATCH v14 1/4] asm-generic,arm64: create task variant of
 access_ok

On 03/29, Gregory Price wrote:
>
> Last note on this before I push up another patch set.
>
> The change from __get_user to get_user also introduces a call to
> might_fault() which adds a larger callstack for every syscall /
> dispatch.  This turns into a might_sleep and might_reschedule, which
> represent a very different pattern of execution from before.

might_fault() is nop unless CONFIG_PROVE_LOCKING || DEBUG_ATOMIC_SLEEP.

Again, I won't really argue with task_access_ok(). Just I am not sure
2/4 gives enough justification for this new helper with unclear semantics
(until we ensure that access_ok() doesn't depend on current).

Oleg.