Re: [RFC PATCH] xen/arm: arm32: Enable smpboot on Arm32 based systems

[Julien Grall <julien@xxxxxxx>]

Hi Stefano,

On 03/05/2023 00:55, Stefano Stabellini wrote:
> > +    {
> > +        printk("CPU%d: No release addr\n", cpu);
> > +        return -ENODEV;
> > +    }
> > +
> > +    release = ioremap_nocache(cpu_release_addr[cpu], 4);
> > +    if ( !release )
> > +    {
> > +        dprintk(XENLOG_ERR, "CPU%d: Unable to map release address\n", cpu);
> > +        return -EFAULT;
> > +    }
> > +
> > +    writel(__pa(init_secondary), release);
> > +
> > +    iounmap(release);
> I think we need a wmb() ?
I am not sure why we would need a wmb() here. Instead, looking at the 
Linux version, I think we are missing a cache flush (so does on arm64) 
which would be necessary if the CPU waiting for the release doesn't have 
cache enabled.
Cheers,

--
Julien Grall