Re: [Xen-devel] [PATCH] xen-blkback: only attach blkback if the required features are met

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Fri, Apr 04, 2014 at 04:41:11PM +0200, 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.

Could you point to the git commit that introduces it in the patch please?
> 
> Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
> Cc: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> Cc: David Vrabel <david.vrabel@xxxxxxxxxx>
> Cc: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
> ---
>  drivers/block/xen-blkback/blkback.c |   12 ++++++++++++
>  include/xen/interface/features.h    |    6 ++++++
>  2 files changed, 18 insertions(+), 0 deletions(-)
> 
> diff --git a/drivers/block/xen-blkback/blkback.c 
> b/drivers/block/xen-blkback/blkback.c
> index 64c60ed..4c23ddd 100644
> --- 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 */
> +
>       rc = xen_blkif_interface_init();
>       if (rc)
>               goto failed_init;
> diff --git a/include/xen/interface/features.h 
> b/include/xen/interface/features.h
> index 131a6cc..d1e0f23 100644
> --- a/include/xen/interface/features.h
> +++ b/include/xen/interface/features.h
> @@ -53,6 +53,12 @@
>  /* operation as Dom0 is supported */
>  #define XENFEAT_dom0                      11
>  
> +/*
> + * If set, GNTTABOP_map_grant_ref sets the proper IOMMU mappings so the
> + * resulting mapped page can be used for IO with hardware devices.
> + */
> +#define XENFEAT_hvm_gntmap_supports_iommu 12
> +
>  #define XENFEAT_NR_SUBMAPS 1
>  
>  #endif /* __XEN_PUBLIC_FEATURES_H__ */
> -- 
> 1.7.7.5 (Apple Git-26)
> 

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