Re: [Xen-devel] [PATCH v5 02/17] Add cmpxchg16b support for x86-64

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Wed, Aug 12, 2015 at 10:35:23AM +0800, Feng Wu wrote:
> This patch adds cmpxchg16b support for x86-64, so software
> can perform 128-bit atomic write/read.
> 
> CC: Keir Fraser <keir@xxxxxxx>
> CC: Jan Beulich <jbeulich@xxxxxxxx>
> CC: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> Signed-off-by: Feng Wu <feng.wu@xxxxxxxxx>
> ---
> v5:
> - Change back the parameters of __cmpxchg16b() to __uint128_t *
> - Remove pointless cast for 'ptr'
> - Remove pointless parentheses
> - Use A constraint for the output
> 
> v4:
> - Use pointer as the parameter of __cmpxchg16b().
> - Use gcc's __uint128_t built-in type
> - Make the parameters of __cmpxchg16b() void *
> 
> v3:
> - Newly added.
> 
>  xen/include/asm-x86/x86_64/system.h | 28 ++++++++++++++++++++++++++++
>  1 file changed, 28 insertions(+)
> 
> diff --git a/xen/include/asm-x86/x86_64/system.h 
> b/xen/include/asm-x86/x86_64/system.h
> index 662813a..ebbe4b5 100644
> --- a/xen/include/asm-x86/x86_64/system.h
> +++ b/xen/include/asm-x86/x86_64/system.h
> @@ -6,6 +6,34 @@
>                                     (unsigned long)(n),sizeof(*(ptr))))
>  
>  /*
> + * Atomic 16 bytes compare and exchange.  Compare OLD with MEM, if
> + * identical, store NEW in MEM.  Return the initial value in MEM.
> + * Success is indicated by comparing RETURN with OLD.
> + *
> + * This function can only be called when cpu_has_cx16 is ture.

s/ture/true/

> + */
> +
> +static always_inline __uint128_t __cmpxchg16b(
> +    volatile void *ptr, __uint128_t *old, __uint128_t *new)
> +{
> +    __uint128_t prev;
> +    uint64_t new_high = *new >> 64;
> +    uint64_t new_low = (uint64_t)*new;
> +
> +    ASSERT(cpu_has_cx16);
> +
> +    asm volatile ( "lock; cmpxchg16b %3"
> +                   : "=A" (prev)
> +                   : "c" (new_high), "b" (new_low), "m" (*__xg(ptr)), "0" 
> (*old)
> +                   : "memory" );
> +
> +    return prev;
> +}
> +
> +#define cmpxchg16b(ptr,o,n)                                             \
> +    __cmpxchg16b((ptr), (__uint128_t *)(o), (__uint128_t *)(n))
> +
> +/*
>   * This function causes value _o to be changed to _n at location _p.
>   * If this access causes a fault then we return 1, otherwise we return 0.
>   * If no fault occurs then _o is updated to the value we saw at _p. If this
> -- 
> 2.1.0
> 
> 
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> http://lists.xen.org/xen-devel

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