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Date:   Fri, 21 Aug 2020 02:18:21 +0000
From:   "Liu, Yi L" <yi.l.liu@...el.com>
To:     Alex Williamson <alex.williamson@...hat.com>
CC:     "eric.auger@...hat.com" <eric.auger@...hat.com>,
        "baolu.lu@...ux.intel.com" <baolu.lu@...ux.intel.com>,
        "joro@...tes.org" <joro@...tes.org>,
        "Tian, Kevin" <kevin.tian@...el.com>,
        "jacob.jun.pan@...ux.intel.com" <jacob.jun.pan@...ux.intel.com>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        "Tian, Jun J" <jun.j.tian@...el.com>,
        "Sun, Yi Y" <yi.y.sun@...el.com>,
        "jean-philippe@...aro.org" <jean-philippe@...aro.org>,
        "peterx@...hat.com" <peterx@...hat.com>,
        "Wu, Hao" <hao.wu@...el.com>,
        "stefanha@...il.com" <stefanha@...il.com>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v6 07/15] vfio/type1: Add VFIO_IOMMU_PASID_REQUEST
 (alloc/free)

Hi Alex,

> From: Alex Williamson <alex.williamson@...hat.com>
> Sent: Friday, August 21, 2020 9:49 AM
> 
> On Fri, 21 Aug 2020 00:37:19 +0000
> "Liu, Yi L" <yi.l.liu@...el.com> wrote:
> 
> > Hi Alex,
> >
> > > From: Alex Williamson <alex.williamson@...hat.com>
> > > Sent: Friday, August 21, 2020 4:51 AM
> > >
> > > On Mon, 27 Jul 2020 23:27:36 -0700
> > > Liu Yi L <yi.l.liu@...el.com> wrote:
> > >
> > > > This patch allows userspace to request PASID allocation/free, e.g.
> > > > when serving the request from the guest.
> > > >
> > > > PASIDs that are not freed by userspace are automatically freed when
> > > > the IOASID set is destroyed when process exits.
> > > >
> > > > Cc: Kevin Tian <kevin.tian@...el.com>
> > > > CC: Jacob Pan <jacob.jun.pan@...ux.intel.com>
> > > > Cc: Alex Williamson <alex.williamson@...hat.com>
> > > > Cc: Eric Auger <eric.auger@...hat.com>
> > > > Cc: Jean-Philippe Brucker <jean-philippe@...aro.org>
> > > > Cc: Joerg Roedel <joro@...tes.org>
> > > > Cc: Lu Baolu <baolu.lu@...ux.intel.com>
> > > > Signed-off-by: Liu Yi L <yi.l.liu@...el.com>
> > > > Signed-off-by: Yi Sun <yi.y.sun@...ux.intel.com>
> > > > Signed-off-by: Jacob Pan <jacob.jun.pan@...ux.intel.com>
> > > > ---
> > > > v5 -> v6:
> > > > *) address comments from Eric against v5. remove the alloc/free helper.
> > > >
> > > > v4 -> v5:
> > > > *) address comments from Eric Auger.
> > > > *) the comments for the PASID_FREE request is addressed in patch 5/15 of
> > > >    this series.
> > > >
> > > > v3 -> v4:
> > > > *) address comments from v3, except the below comment against the range
> > > >    of PASID_FREE request. needs more help on it.
> > > >     "> +if (req.range.min > req.range.max)
> > > >
> > > >      Is it exploitable that a user can spin the kernel for a long time in
> > > >      the case of a free by calling this with [0, MAX_UINT] regardless of
> > > >      their actual allocations?"
> > > >
> > > > https://lore.kernel.org/linux-iommu/20200702151832.048b44d1@x1.home/
> > > >
> > > > v1 -> v2:
> > > > *) move the vfio_mm related code to be a seprate module
> > > > *) use a single structure for alloc/free, could support a range of
> > > > PASIDs
> > > > *) fetch vfio_mm at group_attach time instead of at iommu driver open
> > > > time
> > > > ---
> > > >  drivers/vfio/Kconfig            |  1 +
> > > >  drivers/vfio/vfio_iommu_type1.c | 69
> > > +++++++++++++++++++++++++++++++++++++++++
> > > >  drivers/vfio/vfio_pasid.c       | 10 ++++++
> > > >  include/linux/vfio.h            |  6 ++++
> > > >  include/uapi/linux/vfio.h       | 37 ++++++++++++++++++++++
> > > >  5 files changed, 123 insertions(+)
> > > >
> > > > diff --git a/drivers/vfio/Kconfig b/drivers/vfio/Kconfig index
> > > > 3d8a108..95d90c6 100644
> > > > --- a/drivers/vfio/Kconfig
> > > > +++ b/drivers/vfio/Kconfig
> > > > @@ -2,6 +2,7 @@
> > > >  config VFIO_IOMMU_TYPE1
> > > >  	tristate
> > > >  	depends on VFIO
> > > > +	select VFIO_PASID if (X86)
> > > >  	default n
> > > >
> > > >  config VFIO_IOMMU_SPAPR_TCE
> > > > diff --git a/drivers/vfio/vfio_iommu_type1.c
> > > > b/drivers/vfio/vfio_iommu_type1.c index 18ff0c3..ea89c7c 100644
> > > > --- a/drivers/vfio/vfio_iommu_type1.c
> > > > +++ b/drivers/vfio/vfio_iommu_type1.c
> > > > @@ -76,6 +76,7 @@ struct vfio_iommu {
> > > >  	bool				dirty_page_tracking;
> > > >  	bool				pinned_page_dirty_scope;
> > > >  	struct iommu_nesting_info	*nesting_info;
> > > > +	struct vfio_mm			*vmm;
> > > >  };
> > > >
> > > >  struct vfio_domain {
> > > > @@ -1937,6 +1938,11 @@ static void vfio_iommu_iova_insert_copy(struct
> > > > vfio_iommu *iommu,
> > > >
> > > >  static void vfio_iommu_release_nesting_info(struct vfio_iommu *iommu)
> > > > {
> > > > +	if (iommu->vmm) {
> > > > +		vfio_mm_put(iommu->vmm);
> > > > +		iommu->vmm = NULL;
> > > > +	}
> > > > +
> > > >  	kfree(iommu->nesting_info);
> > > >  	iommu->nesting_info = NULL;
> > > >  }
> > > > @@ -2071,6 +2077,26 @@ static int vfio_iommu_type1_attach_group(void
> > > *iommu_data,
> > > >  					    iommu->nesting_info);
> > > >  		if (ret)
> > > >  			goto out_detach;
> > > > +
> > > > +		if (iommu->nesting_info->features &
> > > > +					IOMMU_NESTING_FEAT_SYSWIDE_PASID)
> > > {
> > > > +			struct vfio_mm *vmm;
> > > > +			int sid;
> > > > +
> > > > +			vmm = vfio_mm_get_from_task(current);
> > > > +			if (IS_ERR(vmm)) {
> > > > +				ret = PTR_ERR(vmm);
> > > > +				goto out_detach;
> > > > +			}
> > > > +			iommu->vmm = vmm;
> > > > +
> > > > +			sid = vfio_mm_ioasid_sid(vmm);
> > > > +			ret = iommu_domain_set_attr(domain->domain,
> > > > +						    DOMAIN_ATTR_IOASID_SID,
> > > > +						    &sid);
> > > > +			if (ret)
> > > > +				goto out_detach;
> > > > +		}
> > > >  	}
> > > >
> > > >  	/* Get aperture info */
> > > > @@ -2859,6 +2885,47 @@ static int vfio_iommu_type1_dirty_pages(struct
> > > vfio_iommu *iommu,
> > > >  	return -EINVAL;
> > > >  }
> > > >
> > > > +static int vfio_iommu_type1_pasid_request(struct vfio_iommu *iommu,
> > > > +					  unsigned long arg)
> > > > +{
> > > > +	struct vfio_iommu_type1_pasid_request req;
> > > > +	unsigned long minsz;
> > > > +	int ret;
> > > > +
> > > > +	minsz = offsetofend(struct vfio_iommu_type1_pasid_request, range);
> > > > +
> > > > +	if (copy_from_user(&req, (void __user *)arg, minsz))
> > > > +		return -EFAULT;
> > > > +
> > > > +	if (req.argsz < minsz || (req.flags & ~VFIO_PASID_REQUEST_MASK))
> > > > +		return -EINVAL;
> > > > +
> > > > +	if (req.range.min > req.range.max)
> > > > +		return -EINVAL;
> > > > +
> > > > +	mutex_lock(&iommu->lock);
> > > > +	if (!iommu->vmm) {
> > > > +		mutex_unlock(&iommu->lock);
> > > > +		return -EOPNOTSUPP;
> > > > +	}
> > > > +
> > > > +	switch (req.flags & VFIO_PASID_REQUEST_MASK) {
> > > > +	case VFIO_IOMMU_FLAG_ALLOC_PASID:
> > > > +		ret = vfio_pasid_alloc(iommu->vmm, req.range.min,
> > > > +				       req.range.max);
> > > > +		break;
> > > > +	case VFIO_IOMMU_FLAG_FREE_PASID:
> > > > +		vfio_pasid_free_range(iommu->vmm, req.range.min,
> > > > +				      req.range.max);
> > > > +		ret = 0;
> > > > +		break;
> > > > +	default:
> > > > +		ret = -EINVAL;
> > > > +	}
> > > > +	mutex_unlock(&iommu->lock);
> > > > +	return ret;
> > > > +}
> > > > +
> > > >  static long vfio_iommu_type1_ioctl(void *iommu_data,
> > > >  				   unsigned int cmd, unsigned long arg)  { @@ -
> > > 2875,6 +2942,8 @@
> > > > static long vfio_iommu_type1_ioctl(void *iommu_data,
> > > >  		return vfio_iommu_type1_unmap_dma(iommu, arg);
> > > >  	case VFIO_IOMMU_DIRTY_PAGES:
> > > >  		return vfio_iommu_type1_dirty_pages(iommu, arg);
> > > > +	case VFIO_IOMMU_PASID_REQUEST:
> > > > +		return vfio_iommu_type1_pasid_request(iommu, arg);
> > > >  	default:
> > > >  		return -ENOTTY;
> > > >  	}
> > > > diff --git a/drivers/vfio/vfio_pasid.c b/drivers/vfio/vfio_pasid.c
> > > > index befcf29..8d0317f 100644
> > > > --- a/drivers/vfio/vfio_pasid.c
> > > > +++ b/drivers/vfio/vfio_pasid.c
> > > > @@ -61,6 +61,7 @@ void vfio_mm_put(struct vfio_mm *vmm)  {
> > > >  	kref_put_mutex(&vmm->kref, vfio_mm_release, &vfio_mm_lock);  }
> > > > +EXPORT_SYMBOL_GPL(vfio_mm_put);
> > > >
> > > >  static void vfio_mm_get(struct vfio_mm *vmm)
> > > >  {
> > > > @@ -114,6 +115,13 @@ struct vfio_mm *vfio_mm_get_from_task(struct
> > > task_struct *task)
> > > >  	mmput(mm);
> > > >  	return vmm;
> > > >  }
> > > > +EXPORT_SYMBOL_GPL(vfio_mm_get_from_task);
> > > > +
> > > > +int vfio_mm_ioasid_sid(struct vfio_mm *vmm)
> > > > +{
> > > > +	return vmm->ioasid_sid;
> > > > +}
> > > > +EXPORT_SYMBOL_GPL(vfio_mm_ioasid_sid);
> > > >
> > > >  /*
> > > >   * Find PASID within @min and @max
> > > > @@ -202,6 +210,7 @@ int vfio_pasid_alloc(struct vfio_mm *vmm, int min, int
> max)
> > > >
> > > >  	return pasid;
> > > >  }
> > > > +EXPORT_SYMBOL_GPL(vfio_pasid_alloc);
> > > >
> > > >  void vfio_pasid_free_range(struct vfio_mm *vmm,
> > > >  			   ioasid_t min, ioasid_t max)
> > > > @@ -218,6 +227,7 @@ void vfio_pasid_free_range(struct vfio_mm *vmm,
> > > >  		vfio_remove_pasid(vmm, vid);
> > > >  	mutex_unlock(&vmm->pasid_lock);
> > > >  }
> > > > +EXPORT_SYMBOL_GPL(vfio_pasid_free_range);
> > > >
> > > >  static int __init vfio_pasid_init(void)
> > > >  {
> > > > diff --git a/include/linux/vfio.h b/include/linux/vfio.h
> > > > index 31472a9..a355d01 100644
> > > > --- a/include/linux/vfio.h
> > > > +++ b/include/linux/vfio.h
> > > > @@ -101,6 +101,7 @@ struct vfio_mm;
> > > >  #if IS_ENABLED(CONFIG_VFIO_PASID)
> > > >  extern struct vfio_mm *vfio_mm_get_from_task(struct task_struct *task);
> > > >  extern void vfio_mm_put(struct vfio_mm *vmm);
> > > > +extern int vfio_mm_ioasid_sid(struct vfio_mm *vmm);
> > > >  extern int vfio_pasid_alloc(struct vfio_mm *vmm, int min, int max);
> > > >  extern void vfio_pasid_free_range(struct vfio_mm *vmm,
> > > >  				  ioasid_t min, ioasid_t max);
> > > > @@ -114,6 +115,11 @@ static inline void vfio_mm_put(struct vfio_mm *vmm)
> > > >  {
> > > >  }
> > > >
> > > > +static inline int vfio_mm_ioasid_sid(struct vfio_mm *vmm)
> > > > +{
> > > > +	return -ENOTTY;
> > > > +}
> > > > +
> > > >  static inline int vfio_pasid_alloc(struct vfio_mm *vmm, int min, int max)
> > > >  {
> > > >  	return -ENOTTY;
> > > > diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
> > > > index 0cf3d6d..6d79557 100644
> > > > --- a/include/uapi/linux/vfio.h
> > > > +++ b/include/uapi/linux/vfio.h
> > > > @@ -1172,6 +1172,43 @@ struct vfio_iommu_type1_dirty_bitmap_get {
> > > >
> > > >  #define VFIO_IOMMU_DIRTY_PAGES             _IO(VFIO_TYPE, VFIO_BASE + 17)
> > > >
> > > > +/**
> > > > + * VFIO_IOMMU_PASID_REQUEST - _IOWR(VFIO_TYPE, VFIO_BASE + 18,
> > > > + *				struct vfio_iommu_type1_pasid_request)
> > > > + *
> > > > + * PASID (Processor Address Space ID) is a PCIe concept for tagging
> > > > + * address spaces in DMA requests. When system-wide PASID allocation
> > > > + * is required by the underlying iommu driver (e.g. Intel VT-d), this
> > > > + * provides an interface for userspace to request pasid alloc/free
> > > > + * for its assigned devices. Userspace should check the availability
> > > > + * of this API by checking VFIO_IOMMU_TYPE1_INFO_CAP_NESTING through
> > > > + * VFIO_IOMMU_GET_INFO.
> > > > + *
> > > > + * @flags=VFIO_IOMMU_FLAG_ALLOC_PASID, allocate a single PASID within
> > > @range.
> > > > + * @flags=VFIO_IOMMU_FLAG_FREE_PASID, free the PASIDs within @range.
> > > > + * @range is [min, max], which means both @min and @max are inclusive.
> > > > + * ALLOC_PASID and FREE_PASID are mutually exclusive.
> > > > + *
> > > > + * returns: allocated PASID value on success, -errno on failure for
> > > > + *	     ALLOC_PASID;
> > > > + *	     0 for FREE_PASID operation;
> > > > + */
> > > > +struct vfio_iommu_type1_pasid_request {
> > > > +	__u32	argsz;
> > > > +#define VFIO_IOMMU_FLAG_ALLOC_PASID	(1 << 0)
> > > > +#define VFIO_IOMMU_FLAG_FREE_PASID	(1 << 1)
> > > > +	__u32	flags;
> > > > +	struct {
> > > > +		__u32	min;
> > > > +		__u32	max;
> > > > +	} range;
> > > > +};
> > >
> > >
> > > IOCTL(2)                   Linux Programmer's Manual                  IOCTL(2)
> > >
> > > NAME
> > >        ioctl - control device
> > >
> > > SYNOPSIS
> > >        #include <sys/ioctl.h>
> > >
> > >        int ioctl(int fd, unsigned long request, ...);
> > >
> > >
> > > ioctl(2) returns a signed int, how can it support returning a __u32
> > > pasid and -errno?  Thanks,
> >
> > yeah, pasid is 20 bits today per PCI spec, so a valid pasid won't use
> > full 32 bits, so I used it. perhaps I need to add a field in the data
> > struct to return allocated pasid. that may be safer. do you think it
> > works?
> 
> AIUI, the pasid is defined as 20 bits, this isn't simply an
> implementation issue, right?  So perhaps it's ok as is and just needs
> some supplemental comments and checking to verify that the desired
> pasid range is valid.  Thanks,

yep. may add some comments. if VFIO ensures the desired pasid range
is valid, then the allocated pasid should be valid all the same. :-)

Regards,
Yi Liu

> Alex

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