On 04/04/14 15:41, Roger Pau Monne wrote:
> Blkback cannot work properly on auto-translated guests if Xen doesn't
> update the IOMMU when performing grant maps/unmaps, so only attach if
> the newly introduced XENFEAT_hvm_gntmap_supports_iommu is found.
Can you explain the problem in more detail and which guest
configurations are affected?
This isn't a problem that is specific to blkback, but any backend that
grant maps and passes the foreign pages to a device so there needs to be
a generic solution.
Why can't this be fixed by having the swiotlb bounce foreign pages?
> --- a/drivers/block/xen-blkback/blkback.c
> +++ b/drivers/block/xen-blkback/blkback.c
> @@ -1381,6 +1381,18 @@ static int __init xen_blkif_init(void)
> if (!xen_domain())
> return -ENODEV;
>
> +#ifdef CONFIG_X86
> + if (xen_feature(XENFEAT_auto_translated_physmap) &&
> + !xen_feature(XENFEAT_hvm_gntmap_supports_iommu)) {
> + /*
> + * blkback cannot work properly on auto-translated guests
> + * if grant table mappings don't update the IOMMU entries.
> + */
> + pr_debug(DRV_PFX "Disabling blkback because Xen is missing
> feature XENFEAT_hvm_gntmap_supports_iommu\n");
> + return -ENODEV;
> + }
> +#endif /* CONFIG_X86 */
Why CONFIG_X86?
David
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