Re: [Xen-devel] [PATCH v2 17/19] xen/arm: Isolate the SError between the context switch of 2 vCPUs

[Julien Grall <julien.grall@xxxxxxx>]

On 30/03/2017 22:49, Stefano Stabellini wrote:
> On Thu, 30 Mar 2017, Wei Chen wrote:
> > +    /*
> > +     * If the SErrors option is "FORWARD", we have to prevent forwarding
> > +     * serror to wrong vCPU. So before context switch, we have to use the
> > +     * synchronize_serror to guarantee that the pending serror would be
> > +     * caught by current vCPU.
> > +     *
> > +     * The SKIP_CTXT_SWITCH_SERROR_SYNC will be set to cpu_hwcaps when the
> > +     * SErrors option is NOT "FORWARD".
> > +     */
> > +    asm volatile(ALTERNATIVE("bl synchronize_serror",
> > +                             "nop",
> > +                             SKIP_CTXT_SWITCH_SERROR_SYNC));
>
> This good, but here you need to add:
>
>   barrier();
>
> because the compiler is free to reorder even asm volatile instructions
> (it could move the asm volatile after __context_switch theoretically).
... or it could moved before hand because there are no barrier... What 
you want to use is asm volatile(ALTERNATIVE(...) : : : "memory");
Cheers,

--
Julien Grall

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
https://lists.xen.org/xen-devel