[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH] xen-blkback: only attach blkback if the required features are met
On 04/04/14 17:01, David Vrabel wrote: > 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? Yes, it could be fixed with that, FreeBSD has been doing it for a long time. But since nobody has complained about this, and the issue has been there for a long time, I'm not sure it's worth adding all the bounce buffer code for what seems to be an unused configuration. Also, since Linux also supports PV, I would just say that if you want to use driver domains you are forced to use PV guests (or have a recent Xen version that properly updates the IOMMU on grant map/unmap). >> --- 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? ARM has a bounce buffer for foreign pages, so this is not needed. > > David > _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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