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

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Date:   Thu, 30 Nov 2017 11:30:01 -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 16:11:35 +0100
Pierre Morel <pmorel@...ux.vnet.ibm.com> wrote:

> On 30/11/2017 15:08, Alex Williamson wrote:
> > 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
> >   
> 
> 
> Yes, I understand that a capability here is a must, I will follow this way.
> 
> For having multiple aperture and MSI protection, I understood it was 
> done using windows and reserved regions.
> Can you point me to my error?

See the thread from Huawei, I don't think that's a solved problem:

https://lists.gnu.org/archive/html/qemu-arm/2017-11/msg00237.html

If you want sysfs to be consumed separately by the user and fed into
new QEMU command line options for creating a VM layout, perhaps that's
sufficient, but I think the vfio api for the iommu should encompass
describing available ranges of mappable iova space without cobbling
together arbitrary info from sysfs.  Thanks,

Alex