RE: [PATCH v7 07/16] vfio/type1: Add VFIO_IOMMU_PASID_REQUEST (alloc/free)

["Liu, Yi L" <yi.l.liu@intel.com>]

Hi Alex,

> From: Alex Williamson <alex.williamson@redhat.com>
> Sent: Saturday, September 12, 2020 5:38 AM
> 
> On Thu, 10 Sep 2020 03:45:24 -0700
> Liu Yi L <yi.l.liu@intel.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@intel.com>
> > CC: Jacob Pan <jacob.jun.pan@linux.intel.com>
> > Cc: Alex Williamson <alex.williamson@redhat.com>
> > Cc: Eric Auger <eric.auger@redhat.com>
> > Cc: Jean-Philippe Brucker <jean-philippe@linaro.org>
> > Cc: Joerg Roedel <joro@8bytes.org>
> > Cc: Lu Baolu <baolu.lu@linux.intel.com>
> > Signed-off-by: Liu Yi L <yi.l.liu@intel.com>
> > Signed-off-by: Yi Sun <yi.y.sun@linux.intel.com>
> > Signed-off-by: Jacob Pan <jacob.jun.pan@linux.intel.com>
> > ---
> > v6 -> v7:
> > *) current VFIO returns allocated pasid via signed int, thus VFIO UAPI
> >    can only support 31 bits pasid. If user space gives min,max which is
> >    wider than 31 bits, should fail the allocation or free request.
> >
> > 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 | 76
> +++++++++++++++++++++++++++++++++++++++++
> >  drivers/vfio/vfio_pasid.c       | 10 ++++++
> >  include/linux/vfio.h            |  6 ++++
> >  include/uapi/linux/vfio.h       | 43 +++++++++++++++++++++++
> >  5 files changed, 136 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 3c0048b..bd4b668 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 {
> > @@ -2000,6 +2001,11 @@ 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;
> >  }
> > @@ -2127,6 +2133,26 @@ 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;
> > +			struct ioasid_set *set;
> > +
> > +			vmm = vfio_mm_get_from_task(current);
> > +			if (IS_ERR(vmm)) {
> > +				ret = PTR_ERR(vmm);
> > +				goto out_detach;
> > +			}
> > +			iommu->vmm = vmm;
> > +
> > +			set = vfio_mm_ioasid_set(vmm);
> > +			ret = iommu_domain_set_attr(domain->domain,
> > +						    DOMAIN_ATTR_IOASID_SET,
> > +						    set);
> > +			if (ret)
> > +				goto out_detach;
> > +		}
> >  	}
> >
> >  	/* Get aperture info */
> > @@ -2908,6 +2934,54 @@ 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;
> > +
> > +	/*
> > +	 * Current VFIO_IOMMU_PASID_REQUEST only supports at most
> > +	 * 31 bits PASID. The min,max value from userspace should
> > +	 * not exceed 31 bits.
> 
> Please describe the source of this restriction.  I think it's due to
> using the ioctl return value to return the PASID, thus excluding the
> negative values, but aren't we actually restricted to pasid_bits
> exposed in the nesting_info? 

yes, the description for this restriction is in the uapi/vfio.h. I
think you are right. We should restricted to the pasid_bits exposed
in the nesting_info. thanks for the spotting.

> If this is just a sanity test for the API
> then why are we defining VFIO_IOMMU_PASID_BITS in the uapi header,
> which causes conflicting information to the user... which do they
> honor? 

yes, it should not be in the uapi header. will fix it.

> Should we instead verify that pasid_bits matches our API scheme
> when configuring the nested domain and then let the ioasid allocator
> reject requests outside of the range?

agreed, I think it may be checked in the attach_group phase, if pasid_bits
from iommu vendor driver are larger than 31 bits, we fail the attach.

> 
> > +	 */
> > +	if (req.range.min > req.range.max ||
> > +	    req.range.min > (1 << VFIO_IOMMU_PASID_BITS) ||
> > +	    req.range.max > (1 << VFIO_IOMMU_PASID_BITS))
> 
> Off by one, >= for the bit test.

got it. thanks for spotting it.

> > +		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;
> 
> Set the initial value when it's declared?

I see, will do. :-)

> > +		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)
> >  {
> > @@ -2924,6 +2998,8 @@ 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 44ecdd5..0ec4660 100644
> > --- a/drivers/vfio/vfio_pasid.c
> > +++ b/drivers/vfio/vfio_pasid.c
> > @@ -60,6 +60,7 @@ 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)
> >  {
> > @@ -113,6 +114,13 @@ struct vfio_mm *vfio_mm_get_from_task(struct
> task_struct *task)
> >  	mmput(mm);
> >  	return vmm;
> >  }
> > +EXPORT_SYMBOL_GPL(vfio_mm_get_from_task);
> > +
> > +struct ioasid_set *vfio_mm_ioasid_set(struct vfio_mm *vmm)
> > +{
> > +	return vmm->ioasid_set;
> > +}
> > +EXPORT_SYMBOL_GPL(vfio_mm_ioasid_set);
> >
> >  /*
> >   * Find PASID within @min and @max
> > @@ -201,6 +209,7 @@ 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)
> > @@ -217,6 +226,7 @@ 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..5c3d7a8 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 struct ioasid_set *vfio_mm_ioasid_set(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 struct ioasid_set *vfio_mm_ioasid_set(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 ff40f9e..a4bc42e 100644
> > --- a/include/uapi/linux/vfio.h
> > +++ b/include/uapi/linux/vfio.h
> > @@ -1172,6 +1172,49 @@ 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.
> > + *
> > + * Current interface supports at most 31 bits PASID bits as returning
> > + * PASID allocation result via signed int. PCIe spec defines 20 bits
> > + * for PASID width, so 31 bits is enough. As a result user space should
> > + * provide min, max no more than 31 bits.
> 
> Perhaps this is the description I was looking for, but this still
> conflicts with what I think the user is supposed to do, which is to
> provide a range within nesting_info.pasid_bits.  These seem like
> implementation details, not uapi.  Thanks,

agreed, I may move this comment (after refining :-)) to the place attach_group
where we check if pasid_bits matches our API scheme, and just put a comment
"userspace should provide a range within nesting_info.pasid_bits" here.

Regards,
Yi Liu

> Alex
> 
> > + * 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;
> > +};
> > +
> > +#define VFIO_PASID_REQUEST_MASK	(VFIO_IOMMU_FLAG_ALLOC_PASID | \
> > +					 VFIO_IOMMU_FLAG_FREE_PASID)
> > +
> > +#define VFIO_IOMMU_PASID_BITS		31
> > +
> > +#define VFIO_IOMMU_PASID_REQUEST	_IO(VFIO_TYPE, VFIO_BASE + 18)
> > +
> >  /* -------- Additional API for SPAPR TCE (Server POWERPC) IOMMU -------- */
> >
> >  /*

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