Re: [Xen-devel] [PATCH 3/4] xen: arm: add barrier before sev in smp_spin_table_cpu_up

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Mon, 2014-03-17 at 13:52 +0000, Ian Campbell wrote:
> This ensures that the writeq to the release address has occurred.
> 
> In reality there is a dsb() in the iounmap() (in the eventual write_pte()) but
> make it explicit.
> 
> The ARMv8 ARM recommends that sev() is usually accompanied by a dsb(), the
> only other uses are in the v7 spinlock code which includes a dsb() already.

Thinking about this some more the dsb() in the ioumap is logical and it
is reasonable to rely on it. This also satisfies the need for a dsb
before the sev.

So I intend to just drop this patch for the next iteration.

> 
> Signed-off-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
> ---
> v2: typos in the commit message
> ---
>  xen/arch/arm/arm64/smpboot.c |    1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/xen/arch/arm/arm64/smpboot.c b/xen/arch/arm/arm64/smpboot.c
> index 9146476..8e2ecf2 100644
> --- a/xen/arch/arm/arm64/smpboot.c
> +++ b/xen/arch/arm/arm64/smpboot.c
> @@ -36,6 +36,7 @@ static int __init smp_spin_table_cpu_up(int cpu)
>  
>      iounmap(release);
>  
> +    dsb(); /* Ensure that the write to cpu_release_addr has occurred. */
>      sev();
>  
>      return cpu_up_send_sgi(cpu);



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