On Fri, Oct 30, 2020 at 07:05:09PM +0100, Jean-Philippe Brucker wrote:
> From: Bharat Bhushan <bbhush...@marvell.com>
>
> The virtio-iommu device can deal with arbitrary page sizes for virtual
> endpoints, but for endpoints assigned with VFIO it must follow the page
> granule used by the host IOMMU driver.
>
> Implement the interface to set the vIOMMU page size mask, called by VFIO
> for each endpoint. We assume that all host IOMMU drivers use the same
> page granule (the host page granule). Override the page_size_mask field
> in the virtio config space.
(Nit: Seems slightly mismatched with the code below)
[...]
> + /*
> + * After the machine is finalized, we can't change the mask anymore. If
> by
> + * chance the hotplugged device supports the same granule, we can still
> + * accept it. Having a different masks is possible but the guest will use
> + * sub-optimal block sizes, so warn about it.
> + */
> + if (qdev_hotplug) {
> + int new_granule = ctz64(new_mask);
> + int cur_granule = ctz64(cur_mask);
> +
> + if (new_granule != cur_granule) {
> + error_setg(errp, "virtio-iommu page mask 0x%"PRIx64
> + " is incompatible with mask 0x%"PRIx64, cur_mask,
> + new_mask);
> + return -1;
> + } else if (new_mask != cur_mask) {
> + warn_report("virtio-iommu page mask 0x%"PRIx64
> + " does not match 0x%"PRIx64, cur_mask, new_mask);
IMHO, new_mask!=cur_mask is ok, as long as it's a superset of reported
cur_mask, then it'll still guarantee to work.
Meanwhile, checking against granule seems not safe enough if the guest driver
started to use huge pages in iommu pgtables...
In summary:
if (qdev_hotplug) {
if ((new_mask & cur_mask) == cur_mask) {
/* Superset of old mask; we're good. Keep the old mask since same
*/
return 0;
} else {
/* Guest driver can use any psize in cur_mask, not safe to continue
*/
error_setg(...);
return -1;
}
}
Maybe we can also work on top too (if this is the only reason to repost,
especially if Michael would like to pick this up sooner), so I just raise this
up.
Thanks,
--
Peter Xu
