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

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Date:   Mon, 24 Oct 2022 13:13:18 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Linus Torvalds <torvalds@...ux-foundation.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 10:53:42AM -0700, Linus Torvalds wrote:
> 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()".

Regular xchg64() didn't work, the casting crud there is required because
of how pxx_t is a struct.

Now I could obviously do a xchg64(), but then we'd still need this
wrapper -- and yeah, I don't know how many other users there are.