Re: [Xen-devel] [PATCH 2/2] x86/pae: use 64 bit atomic xchg function in native_ptep_get_and_clear

[Jan Beulich]

>>> On 20.08.18 at 07:14, <jgross@xxxxxxxx> 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