linux-kernel - Re: [PATCH v0.7 2/5] mm, x86/uaccess: add userspace atomic helpers

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Date:   Tue, 26 Oct 2021 16:21:55 -0700
From:   Peter Oskolkov <posk@...k.io>
To:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>, linux-mm@...ck.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-api@...r.kernel.org
Cc:     Paul Turner <pjt@...gle.com>, Ben Segall <bsegall@...gle.com>,
        Peter Oskolkov <posk@...gle.com>,
        Andrei Vagin <avagin@...gle.com>, Jann Horn <jannh@...gle.com>,
        Thierry Delisle <tdelisle@...terloo.ca>
Subject: Re: [PATCH v0.7 2/5] mm, x86/uaccess: add userspace atomic helpers

On Tue, Oct 12, 2021 at 4:25 PM Peter Oskolkov <posk@...k.io> wrote:

[...]

> +static inline int __try_xchg_user_32(u32 *oval, u32 __user *uaddr, u32 newval)
> +{
> +       u32 oldval = 0;
> +       int ret = 0;
> +
> +       asm volatile("\n"
> +               "1:\txchgl %0, %2\n"
> +               "2:\n"
> +               "\t.section .fixup, \"ax\"\n"
> +               "3:\tmov     %3, %0\n"

I believe the line above should be "mov %3, %1", not "mov %3, %0".
I'll fix this in the next patchset mailing.

> +               "\tjmp     2b\n"
> +               "\t.previous\n"
> +               _ASM_EXTABLE_UA(1b, 3b)
> +               : "=r" (oldval), "=r" (ret), "+m" (*uaddr)
> +               : "i" (-EFAULT), "0" (newval), "1" (0)
> +       );
> +
> +       if (ret)
> +               return ret;
> +
> +       *oval = oldval;
> +       return 0;
> +}
> +
> +static inline int __try_xchg_user_64(u64 *oval, u64 __user *uaddr, u64 newval)
> +{> +> +
> +       u64 oldval = 0;
> +       int ret = 0;
> +
> +       asm volatile("\n"
> +               "1:\txchgq %0, %2\n"
> +               "2:\n"
> +               "\t.section .fixup, \"ax\"\n"
> +               "3:\tmov     %3, %0\n"

Same here.

[...]