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Date:   Mon, 20 Aug 2018 02:40:12 -0600
From:   "Jan Beulich" <JBeulich@suse.com>
To:     "Juergen Gross" <jgross@suse.com>
Cc:     "the arch/x86 maintainers" <x86@kernel.org>, <tglx@linutronix.de>,
        "xen-devel" <xen-devel@lists.xenproject.org>,
        "Boris Ostrovsky" <boris.ostrovsky@oracle.com>, <mingo@redhat.com>,
        <linux-kernel@vger.kernel.org>, <hpa@zytor.com>
Subject: Re: [Xen-devel] [PATCH 2/2] x86/pae: use 64 bit atomic xchg
 function in native_ptep_get_and_clear
References: <20180820051456.20779-1-jgross@suse.com>
 <20180820051456.20779-3-jgross@suse.com>
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>>> On 20.08.18 at 07:14, <jgross@suse.com> wrote:
> @@ -148,14 +150,14 @@ static inline void pud_clear(pud_t *pudp)
>  #ifdef CONFIG_SMP
>  static inline pte_t native_ptep_get_and_clear(pte_t *ptep)
>  {
> -	pte_t res;
> +	union {
> +		pte_t pte;
> +		long long val;
> +	} res;

Why the union? pte_t already is one, with the pte field being what
you're after ...

> -	/* xchg acts as a barrier before the setting of the high bits */
> -	res.pte_low = xchg(&ptep->pte_low, 0);
> -	res.pte_high = ptep->pte_high;
> -	ptep->pte_high = 0;
> +	res.val = arch_atomic64_xchg((atomic64_t *)ptep, 0);

... here.

Jan