Re: [PATCH v3 1/3] xen/arm: gic: Check the size of the CPU and vCPU interface retrieved from DT

[Julien Grall <julien.grall@citrix.com>]

On 06/10/15 15:11, Ian Campbell wrote:
> On Mon, 2015-10-05 at 15:17 +0100, Julien Grall wrote:
>> @@ -641,7 +643,29 @@ static int __init gicv2_init(void)
>>          panic("GICv2: Cannot find the maintenance IRQ");
>>      gicv2_info.maintenance_irq = res;
>>  
>> -    /* TODO: Add check on distributor, cpu size */
>> +    /* TODO: Add check on distributor */
>> +
>> +    /*
>> +     * The GICv2 CPU interface should at least be 8KB. Although, most of the DT
>> +     * doesn't correctly set it and use the GICv1 CPU interface size (i.e 4KB).
>> +     * Warn and then fixup.
>> +     */
>> +    if ( csize < SZ_8K )
>> +    {
>> +        printk(XENLOG_WARNING "GICv2: WARNING: "
>> +               "The GICC size is wrong: %#"PRIx64" expected %#x\n",
>> +               csize, SZ_8K);
> 
> "is too small"?

Ok.

> 
>> +        csize = SZ_8K;
>> +    }
>> +
>> +    /*
>> +     * Check if the CPU interface and virtual CPU interface have the
>> +     * same size.
>> +     */
>> +    if ( csize != vsize )
>> +        printk(XENLOG_WARNING "GICv2: WARNING: "
>> +               "Sizes of GICC (%#"PRIpaddr") and GICV (%#"PRIpaddr") don't match\n",
>> +               csize, vsize);
> 
> Should we also force them to be equal? Either
> 	csize = vsize = min(csize,vsize)

If we restrict csize we will get to some other troubles later because
vsize may be only 4KB.

> or
> 	vsize = csize
> 
> (probably the first)?

None of them.

>  
>> +    /*
>> +     * Only allow support of GICv2 compatible when the CPU interface
>> +     * and virtual CPU interface are 8KB
>> +     * XXX: Handle other size?
>> +     */
>> +    if ( csize != SZ_8K && vsize != SZ_8K )
> 
> I think you meant || ? Otherwise this is happy so long as one of them is
> right rather than requiring both of them to be 8K.

Right.

> 
> WRT to the XXX I think I'd be happier if this was < SZ_8K for each.
> Otherwise some future GIC which is compatible but has extensions to the
> register space would needlessly require changes here. But I can live with
> this.

The GICv2 CPU interface is always at least 8KB. Having an higher value
may mean that the GIC is aliased.

GICv2 on GICv3 is only used for guest. I prefer to restrict the usage to
known and safe value until we have someone using different size.

This will avoid to expose unwanted data/value to a guest.

Regards,

-- 
Julien Grall