linux-kernel - Re: [PATCH] vfio/iommu_type1: report the IOMMU aperture info

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Message-ID: <20171130070844.7d6c5053@t450s.home>
Date:   Thu, 30 Nov 2017 07:08:44 -0700
From:   Alex Williamson <alex.williamson@...hat.com>
To:     Pierre Morel <pmorel@...ux.vnet.ibm.com>
Cc:     cohuck@...hat.com, borntraeger@...ibm.com,
        zyimin@...ux.vnet.ibm.com, pasic@...ux.vnet.ibm.com,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] vfio/iommu_type1: report the IOMMU aperture info

On Thu, 30 Nov 2017 12:34:38 +0100
Pierre Morel <pmorel@...ux.vnet.ibm.com> wrote:

> When userland VFIO defines a new IOMMU for a guest it may
> want to specify to the guest the physical limits of
> the underlying host IOMMU to avoid access to forbidden
> memory ranges.
> 
> Currently, the vfio_iommu_type1 driver does not report this
> information to userland.
> 
> Let's extend the vfio_iommu_type1_info structure reported
> by the ioctl VFIO_IOMMU_GET_INFO command to report the
> IOMMU limits as new uint64_t entries aperture_start and
> aperture_end.
> 
> Let's also extend the flags bit map to add a flag specifying
> if this extension of the info structure is reported or not.
> 
> Signed-off-by: Pierre Morel <pmorel@...ux.vnet.ibm.com>
> ---
>  drivers/vfio/vfio_iommu_type1.c | 42 +++++++++++++++++++++++++++++++++++++++++
>  include/uapi/linux/vfio.h       |  3 +++
>  2 files changed, 45 insertions(+)
> 
> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
> index 8549cb1..7da5fe0 100644
> --- a/drivers/vfio/vfio_iommu_type1.c
> +++ b/drivers/vfio/vfio_iommu_type1.c
> @@ -1526,6 +1526,40 @@ static int vfio_domains_have_iommu_cache(struct vfio_iommu *iommu)
>  	return ret;
>  }
>  
> +/**
> + * vfio_get_aperture - report minimal aperture of a vfio_iommu
> + * @iommu: the current vfio_iommu
> + * @start: a pointer to the aperture start
> + * @end  : a pointer to the aperture end
> + *
> + * This function iterate on the domains using the given vfio_iommu
> + * and restrict the aperture to the minimal aperture common
> + * to all domains sharing this vfio_iommu.
> + */
> +static void vfio_get_aperture(struct vfio_iommu *iommu, uint64_t *start,
> +				uint64_t *end)
> +{
> +	struct iommu_domain_geometry geometry;
> +	struct vfio_domain *domain;
> +
> +	*start = 0;
> +	*end = U64_MAX;
> +
> +	mutex_lock(&iommu->lock);
> +	/* loop on all domains using this vfio_iommu */
> +	list_for_each_entry(domain, &iommu->domain_list, next) {
> +		iommu_domain_get_attr(domain->domain, DOMAIN_ATTR_GEOMETRY,
> +					&geometry);
> +		if (geometry.force_aperture) {
> +			if (geometry.aperture_start > *start)
> +				*start = geometry.aperture_start;
> +			if (geometry.aperture_end < *end)
> +				*end = geometry.aperture_end;
> +		}
> +	}
> +	mutex_unlock(&iommu->lock);
> +}
> +
>  static long vfio_iommu_type1_ioctl(void *iommu_data,
>  				   unsigned int cmd, unsigned long arg)
>  {
> @@ -1560,6 +1594,14 @@ static long vfio_iommu_type1_ioctl(void *iommu_data,
>  
>  		info.iova_pgsizes = vfio_pgsize_bitmap(iommu);
>  
> +		minsz = min_t(size_t, info.argsz, sizeof(info));
> +		if (minsz >= offsetofend(struct vfio_iommu_type1_info,
> +					 aperture_end)) {
> +			info.flags |= VFIO_IOMMU_INFO_APERTURE;
> +			vfio_get_aperture(iommu, &info.aperture_start,
> +					  &info.aperture_end);
> +		}
> +
>  		return copy_to_user((void __user *)arg, &info, minsz) ?
>  			-EFAULT : 0;
>  
> diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
> index 0fb25fb..780d909 100644
> --- a/include/uapi/linux/vfio.h
> +++ b/include/uapi/linux/vfio.h
> @@ -519,6 +519,9 @@ struct vfio_iommu_type1_info {
>  	__u32	flags;
>  #define VFIO_IOMMU_INFO_PGSIZES (1 << 0)	/* supported page sizes info */
>  	__u64	iova_pgsizes;		/* Bitmap of supported page sizes */
> +#define VFIO_IOMMU_INFO_APERTURE (1 << 1)	/* supported aperture info */
> +	__u64   aperture_start;		/* start of DMA aperture */
> +	__u64   aperture_end;		/* end of DMA aperture */
>  };
>  
>  #define VFIO_IOMMU_GET_INFO _IO(VFIO_TYPE, VFIO_BASE + 12)

This only supports the most simple topology, even x86 cannot claim to
have a single contiguous aperture, it's typically bisected by an MSI
window.  I think we need an API that supports one or more apertures
out of the box.  Also as Eric indicates, a capability is probably the
better option for creating a flexible structure.  Thanks,

Alex