linux-kernel - Re: [PATCH 10/13] x86/mm/pae: Be consistent with pXXp_get_and

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Message-ID: <CAHk-=wh6ip4AVqGx6kB9aHN07pR3M4htTTq1n=M7skPaudpM-Q@mail.gmail.com>
Date:   Sat, 22 Oct 2022 10:53:42 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     x86@...nel.org, willy@...radead.org, akpm@...ux-foundation.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        aarcange@...hat.com, kirill.shutemov@...ux.intel.com,
        jroedel@...e.de, ubizjak@...il.com
Subject: Re: [PATCH 10/13] x86/mm/pae: Be consistent with pXXp_get_and_clear()

On Sat, Oct 22, 2022 at 4:48 AM Peter Zijlstra <peterz@...radead.org> wrote:
>
> +
> +#define pxx_xchg64(_pxx, _ptr, _val) ({                                        \
> +       _pxx##val_t *_p = (_pxx##val_t *)_ptr;                          \
> +       _pxx##val_t _o = *_p;                                           \
> +       do { } while (!try_cmpxchg64(_p, &_o, (_val)));                 \
> +       native_make_##_pxx(_o);                                         \
> +})

I think this could just be a "xchp64()", but if the pte/pmd code is
the only thing that actually wants this on 32-bit architectures, I'm
certainly ok with making it be specific to just this code, and calling
it "pxx_xchg()".

I wonder if there's some driver somewhere that wanted to use it, but
just made it be

        depends on CONFIG_64BIT

instead, or made it use a cmpxchg64() loop because a plain xchg() didn't work.

I guess it really doesn't matter, with 32-bit being relegated to
legacy status anyway. No need to try to expand usage.

                 Linus