linux-kernel - Re: [RFC PATCH v4 02/10] VFIO_IOMMU_TYPE1: Introduce the VFIO_DMA_MAP_FLAG

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Date:	Mon, 10 Feb 2014 13:04:10 -0700
From:	Alex Williamson <alex.williamson@...hat.com>
To:	Antonios Motakis <a.motakis@...tualopensystems.com>
Cc:	kvmarm@...ts.cs.columbia.edu, iommu@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org, gregkh@...uxfoundation.org,
	tech@...tualopensystems.com, a.rigo@...tualopensystems.com,
	B08248@...escale.com, kim.phillips@...aro.org,
	jan.kiszka@...mens.com, kvm@...r.kernel.org, R65777@...escale.com,
	B07421@...escale.com, christoffer.dall@...aro.org, agraf@...e.de,
	B16395@...escale.com, will.deacon@....com
Subject: Re: [RFC PATCH v4 02/10] VFIO_IOMMU_TYPE1: Introduce the
 VFIO_DMA_MAP_FLAG_EXEC flag

On Sat, 2014-02-08 at 18:29 +0100, Antonios Motakis wrote:
> The ARM SMMU driver expects the IOMMU_EXEC flag, otherwise it will
> set the page tables for a device as XN (execute never). This affects
> devices such as the ARM PL330 DMA Controller, which fails to operate
> if the XN flag is set on the memory it tries to fetch its instructions
> from.
> 
> We introduce the VFIO_DMA_MAP_FLAG_EXEC to VFIO, and use it in
> VFIO_IOMMU_TYPE1 to set the IOMMU_EXEC flag. This way the user can
> control whether the XN flag will be set on the requested mappings.

Should the user be told whether this flag is available?  It looks like
existing iommu drivers for x86 ignore the flag, can we count on that?
Thanks,

Alex

> Signed-off-by: Antonios Motakis <a.motakis@...tualopensystems.com>
> ---
>  drivers/vfio/vfio_iommu_type1.c | 5 ++++-
>  include/uapi/linux/vfio.h       | 1 +
>  2 files changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
> index 4fb7a8f..ad7a1f6 100644
> --- a/drivers/vfio/vfio_iommu_type1.c
> +++ b/drivers/vfio/vfio_iommu_type1.c
> @@ -557,6 +557,8 @@ static int vfio_dma_do_map(struct vfio_iommu *iommu,
>  		prot |= IOMMU_WRITE;
>  	if (map->flags & VFIO_DMA_MAP_FLAG_READ)
>  		prot |= IOMMU_READ;
> +	if (map->flags & VFIO_DMA_MAP_FLAG_EXEC)
> +		prot |= IOMMU_EXEC;
>  
>  	if (!prot)
>  		return -EINVAL; /* No READ/WRITE? */
> @@ -865,7 +867,8 @@ static long vfio_iommu_type1_ioctl(void *iommu_data,
>  	} else if (cmd == VFIO_IOMMU_MAP_DMA) {
>  		struct vfio_iommu_type1_dma_map map;
>  		uint32_t mask = VFIO_DMA_MAP_FLAG_READ |
> -				VFIO_DMA_MAP_FLAG_WRITE;
> +				VFIO_DMA_MAP_FLAG_WRITE |
> +				VFIO_DMA_MAP_FLAG_EXEC;
>  
>  		minsz = offsetofend(struct vfio_iommu_type1_dma_map, size);
>  
> diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
> index 0fd47f5..d8e9e99 100644
> --- a/include/uapi/linux/vfio.h
> +++ b/include/uapi/linux/vfio.h
> @@ -392,6 +392,7 @@ 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) */



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