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

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Message-ID: <20140404165851.GS19478@phenom.dumpdata.com>
Date:	Fri, 4 Apr 2014 12:58:51 -0400
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	Roger Pau Monne <roger.pau@...rix.com>
Cc:	xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org,
	David Vrabel <david.vrabel@...rix.com>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>
Subject: Re: [PATCH] xen-blkback: only attach blkback if the required
 features are met

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@...rix.com>
> Cc: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
> Cc: David Vrabel <david.vrabel@...rix.com>
> Cc: Boris Ostrovsky <boris.ostrovsky@...cle.com>
> ---
>  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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