Messages in this thread | | | Date | Fri, 4 Apr 2014 16:01:58 +0100 | From | David Vrabel <> | Subject | Re: [PATCH] xen-blkback: only attach blkback if the required features are met |
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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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