Re: [PATCH v8 13/14] tools/libxl: explicitly grant access to needed I/O-memory ranges

["Jan Beulich" <JBeulich@suse.com>]

>>> On 25.05.14 at 19:08, <julien.grall@linaro.org> wrote:
> On 25/05/14 11:51, Arianna Avanzini wrote:
>> +
>> +        /*
>> +         * If VGA passthru is enabled by domain config, be sure that the
>> +         * domain can access VGA-related iomem regions.
>> +         */
>> +        if (d_config->b_info.u.hvm.gfx_passthru.val) {
>> +            uint64_t vga_iomem_start = 0xa0000 >> XC_PAGE_SHIFT;
>> +            ret = xc_domain_iomem_permission(CTX->xch, domid,
>> +                                             vga_iomem_start, 0x20, 1);
>> +            if (ret < 0) {
>> +                LOGE(ERROR,
>> +                     "failed to give dom%d access to iomem range "
>> +                     "%"PRIx64"-%"PRIx64" for VGA passthru",
>> +                     domid, vga_iomem_start, (vga_iomem_start + 0x20 - 1));
>> +                goto error_out;
>> +            }
>> +        }
> 
> IHMO, the guest doesn't need to have permission to this region. When 
> QEMU ask to map this region to the guest, the hypercall will only check 
> the permission on the domain where QEMU is running. Therefore, the 
> permission should be given to the stubdomain.

How would qemu be involved in I/O from/to a passed through
device?

Jan