Re: [Qemu-devel] [RFC v2 1/4] Add EXEC_FLAG to VFIO DMA mappings

[Eric Auger <eric.auger@linaro.org>]

On 05/11/2014 07:13 PM, Alvise Rigo wrote:
> The flag is mandatory for the ARM SMMU so we always add it if the MMIO
> handles it.

Hi Alvise,

Refering to the root problem explanation found in
https://lkml.org/lkml/2014/2/8/176, I understand the problem is specific
to devices that fetch instructions from executable memory region
sections (XN =0).

Typically this is not the case of Midway xgmac which does not need
executable regions and hence does not need that change.

in
http://lists.linuxfoundation.org/pipermail/iommu/2013-November/007095.html,
Will says most IOMMU mappings should be XN.

I am not knowledged enough on mem mapping settings to understand the
consequences of always setting XN=0, even for devices that do not need
request it.

Does anyone have an opinion on this?

Best Regards

Eric

> 
> Signed-off-by: Alvise Rigo <a.rigo@virtualopensystems.com>
> ---
>  hw/vfio/common.c           | 9 +++++++++
>  hw/vfio/vfio-common.h      | 1 +
>  linux-headers/linux/vfio.h | 2 ++
>  3 files changed, 12 insertions(+)
> 
> diff --git a/hw/vfio/common.c b/hw/vfio/common.c
> index 9d1f723..a805c5d 100644
> --- a/hw/vfio/common.c
> +++ b/hw/vfio/common.c
> @@ -107,6 +107,11 @@ static int vfio_dma_map(VFIOContainer *container, hwaddr iova,
>          map.flags |= VFIO_DMA_MAP_FLAG_WRITE;
>      }
>  
> +    /* add exec flag */
> +    if (container->iommu_data.has_exec_cap) {
> +        map.flags |= VFIO_DMA_MAP_FLAG_EXEC;
> +    }
> +
>      /*
>       * Try the mapping, if it fails with EBUSY, unmap the region and try
>       * again.  This shouldn't be necessary, but we sometimes see it in
> @@ -352,6 +357,10 @@ static int vfio_connect_container(VFIOGroup *group)
>              return -errno;
>          }
>  
> +        if (ioctl(fd, VFIO_CHECK_EXTENSION, VFIO_IOMMU_PROT_EXEC)) {
> +            container->iommu_data.has_exec_cap = true;
> +        }
> +
>          container->iommu_data.type1.listener = vfio_memory_listener;
>          container->iommu_data.release = vfio_listener_release;
>  
> diff --git a/hw/vfio/vfio-common.h b/hw/vfio/vfio-common.h
> index 21148ef..1abbd1a 100644
> --- a/hw/vfio/vfio-common.h
> +++ b/hw/vfio/vfio-common.h
> @@ -35,6 +35,7 @@ typedef struct VFIOContainer {
>          union {
>              VFIOType1 type1;
>          };
> +        bool has_exec_cap; /* support of exec capability by the IOMMU */
>          void (*release)(struct VFIOContainer *);
>      } iommu_data;
>      QLIST_HEAD(, VFIOGroup) group_list;
> diff --git a/linux-headers/linux/vfio.h b/linux-headers/linux/vfio.h
> index 17c58e0..95a02c5 100644
> --- a/linux-headers/linux/vfio.h
> +++ b/linux-headers/linux/vfio.h
> @@ -24,6 +24,7 @@
>  #define VFIO_TYPE1_IOMMU		1
>  #define VFIO_SPAPR_TCE_IOMMU		2
>  
> +#define VFIO_IOMMU_PROT_EXEC		5
>  /*
>   * The IOCTL interface is designed for extensibility by embedding the
>   * structure length (argsz) and flags into structures passed between
> @@ -392,6 +393,7 @@ struct vfio_iommu_type1_dma_map {
>  	__u32	flags;
>  #define VFIO_DMA_MAP_FLAG_READ (1 << 0)		/* readable from device */
>  #define VFIO_DMA_MAP_FLAG_WRITE (1 << 1)	/* writable from device */
> +#define VFIO_DMA_MAP_FLAG_EXEC (1 << 2)	/* executable from device */
>  	__u64	vaddr;				/* Process virtual address */
>  	__u64	iova;				/* IO virtual address */
>  	__u64	size;				/* Size of mapping (bytes) */
>