Re: [PATCH v13 Kernel 4/7] vfio iommu: Implementation of ioctl to for dirty pages tracking.

[Alex Williamson <alex.williamson@redhat.com>]

On Wed, 18 Mar 2020 12:13:12 +0000
"Dr. David Alan Gilbert" <dgilbert@redhat.com> wrote:

> * Kirti Wankhede (kwankhede@nvidia.com) wrote:
> > VFIO_IOMMU_DIRTY_PAGES ioctl performs three operations:
> > - Start pinned and unpinned pages tracking while migration is active
> > - Stop pinned and unpinned dirty pages tracking. This is also used to
> >   stop dirty pages tracking if migration failed or cancelled.
> > - Get dirty pages bitmap. This ioctl returns bitmap of dirty pages, its
> >   user space application responsibility to copy content of dirty pages
> >   from source to destination during migration.
> > 
> > To prevent DoS attack, memory for bitmap is allocated per vfio_dma
> > structure. Bitmap size is calculated considering smallest supported page
> > size. Bitmap is allocated when dirty logging is enabled for those
> > vfio_dmas whose vpfn list is not empty or whole range is mapped, in
> > case of pass-through device.
> > 
> > Bitmap is populated for already pinned pages when bitmap is allocated for
> > a vfio_dma with the smallest supported page size. Update bitmap from
> > pinning and unpinning functions. When user application queries bitmap,
> > check if requested page size is same as page size used to populated
> > bitmap. If it is equal, copy bitmap, but if not equal, return error.
> > 
> > Signed-off-by: Kirti Wankhede <kwankhede@nvidia.com>
> > Reviewed-by: Neo Jia <cjia@nvidia.com>
> > ---
> >  drivers/vfio/vfio_iommu_type1.c | 243 +++++++++++++++++++++++++++++++++++++++-
> >  1 file changed, 237 insertions(+), 6 deletions(-)
> > 
> > diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
> > index d386461e5d11..435e84269a28 100644
> > --- a/drivers/vfio/vfio_iommu_type1.c
> > +++ b/drivers/vfio/vfio_iommu_type1.c
> > @@ -70,6 +70,7 @@ struct vfio_iommu {
> >  	unsigned int		dma_avail;
> >  	bool			v2;
> >  	bool			nesting;
> > +	bool			dirty_page_tracking;
> >  };
> >  
> >  struct vfio_domain {
> > @@ -90,6 +91,7 @@ struct vfio_dma {
> >  	bool			lock_cap;	/* capable(CAP_IPC_LOCK) */
> >  	struct task_struct	*task;
> >  	struct rb_root		pfn_list;	/* Ex-user pinned pfn list */
> > +	unsigned long		*bitmap;
> >  };
> >  
> >  struct vfio_group {
> > @@ -125,6 +127,7 @@ struct vfio_regions {
> >  					(!list_empty(&iommu->domain_list))
> >  
> >  static int put_pfn(unsigned long pfn, int prot);
> > +static unsigned long vfio_pgsize_bitmap(struct vfio_iommu *iommu);
> >  
> >  /*
> >   * This code handles mapping and unmapping of user data buffers
> > @@ -174,6 +177,76 @@ static void vfio_unlink_dma(struct vfio_iommu *iommu, struct vfio_dma *old)
> >  	rb_erase(&old->node, &iommu->dma_list);
> >  }
> >  
> > +static inline unsigned long dirty_bitmap_bytes(unsigned int npages)
> > +{
> > +	if (!npages)
> > +		return 0;
> > +
> > +	return ALIGN(npages, BITS_PER_LONG) / sizeof(unsigned long);
> > +}
> > +
> > +static int vfio_dma_bitmap_alloc(struct vfio_dma *dma, unsigned long pgsize)
> > +{
> > +	if (!RB_EMPTY_ROOT(&dma->pfn_list) || dma->iommu_mapped) {
> > +		unsigned long npages = dma->size / pgsize;
> > +
> > +		dma->bitmap = kvzalloc(dirty_bitmap_bytes(npages), GFP_KERNEL);
> > +		if (!dma->bitmap)
> > +			return -ENOMEM;
> > +	}
> > +	return 0;
> > +}
> > +
> > +static int vfio_dma_all_bitmap_alloc(struct vfio_iommu *iommu,
> > +				     unsigned long pgsize)
> > +{
> > +	struct rb_node *n = rb_first(&iommu->dma_list);
> > +	int ret;
> > +
> > +	for (; n; n = rb_next(n)) {
> > +		struct vfio_dma *dma = rb_entry(n, struct vfio_dma, node);
> > +		struct rb_node *n;
> > +
> > +		ret = vfio_dma_bitmap_alloc(dma, pgsize);
> > +		if (ret) {
> > +			struct rb_node *p = rb_prev(n);
> > +
> > +			for (; p; p = rb_prev(p)) {
> > +				struct vfio_dma *dma = rb_entry(n,
> > +							struct vfio_dma, node);
> > +
> > +				kfree(dma->bitmap);
> > +				dma->bitmap = NULL;
> > +			}
> > +			return ret;
> > +		}
> > +
> > +		if (!dma->bitmap)
> > +			continue;
> > +
> > +		for (n = rb_first(&dma->pfn_list); n; n = rb_next(n)) {
> > +			struct vfio_pfn *vpfn = rb_entry(n, struct vfio_pfn,
> > +							 node);
> > +
> > +			bitmap_set(dma->bitmap,
> > +				   (vpfn->iova - dma->iova) / pgsize, 1);
> > +		}
> > +	}
> > +	return 0;
> > +}
> > +
> > +static void vfio_dma_all_bitmap_free(struct vfio_iommu *iommu)
> > +{
> > +	struct rb_node *n = rb_first(&iommu->dma_list);
> > +
> > +	for (; n; n = rb_next(n)) {
> > +		struct vfio_dma *dma = rb_entry(n, struct vfio_dma, node);
> > +
> > +		kfree(dma->bitmap);
> > +		dma->bitmap = NULL;
> > +	}
> > +}
> > +
> >  /*
> >   * Helper Functions for host iova-pfn list
> >   */
> > @@ -254,12 +327,16 @@ static struct vfio_pfn *vfio_iova_get_vfio_pfn(struct vfio_dma *dma,
> >  	return vpfn;
> >  }
> >  
> > -static int vfio_iova_put_vfio_pfn(struct vfio_dma *dma, struct vfio_pfn *vpfn)
> > +static int vfio_iova_put_vfio_pfn(struct vfio_dma *dma, struct vfio_pfn *vpfn,
> > +				  bool do_tracking, unsigned long pgsize)
> >  {
> >  	int ret = 0;
> >  
> >  	vpfn->ref_count--;
> >  	if (!vpfn->ref_count) {
> > +		if (do_tracking && dma->bitmap)
> > +			bitmap_set(dma->bitmap,
> > +				   (vpfn->iova - dma->iova) / pgsize, 1);
> >  		ret = put_pfn(vpfn->pfn, dma->prot);
> >  		vfio_remove_from_pfn_list(dma, vpfn);
> >  	}
> > @@ -484,7 +561,8 @@ static int vfio_pin_page_external(struct vfio_dma *dma, unsigned long vaddr,
> >  }
> >  
> >  static int vfio_unpin_page_external(struct vfio_dma *dma, dma_addr_t iova,
> > -				    bool do_accounting)
> > +				    bool do_accounting, bool do_tracking,
> > +				    unsigned long pgsize)
> >  {
> >  	int unlocked;
> >  	struct vfio_pfn *vpfn = vfio_find_vpfn(dma, iova);
> > @@ -492,7 +570,7 @@ static int vfio_unpin_page_external(struct vfio_dma *dma, dma_addr_t iova,
> >  	if (!vpfn)
> >  		return 0;
> >  
> > -	unlocked = vfio_iova_put_vfio_pfn(dma, vpfn);
> > +	unlocked = vfio_iova_put_vfio_pfn(dma, vpfn, do_tracking, pgsize);
> >  
> >  	if (do_accounting)
> >  		vfio_lock_acct(dma, -unlocked, true);
> > @@ -563,9 +641,26 @@ static int vfio_iommu_type1_pin_pages(void *iommu_data,
> >  
> >  		ret = vfio_add_to_pfn_list(dma, iova, phys_pfn[i]);
> >  		if (ret) {
> > -			vfio_unpin_page_external(dma, iova, do_accounting);
> > +			vfio_unpin_page_external(dma, iova, do_accounting,
> > +						 false, 0);
> >  			goto pin_unwind;
> >  		}
> > +
> > +		if (iommu->dirty_page_tracking) {
> > +			unsigned long pgshift =
> > +					 __ffs(vfio_pgsize_bitmap(iommu));
> > +
> > +			if (!dma->bitmap) {
> > +				ret = vfio_dma_bitmap_alloc(dma, 1 << pgshift);
> > +				if (ret) {
> > +					vfio_unpin_page_external(dma, iova,
> > +						 do_accounting, false, 0);
> > +					goto pin_unwind;
> > +				}
> > +			}
> > +			bitmap_set(dma->bitmap,
> > +				   (vpfn->iova - dma->iova) >> pgshift, 1);
> > +		}
> >  	}
> >  
> >  	ret = i;
> > @@ -578,7 +673,7 @@ static int vfio_iommu_type1_pin_pages(void *iommu_data,
> >  
> >  		iova = user_pfn[j] << PAGE_SHIFT;
> >  		dma = vfio_find_dma(iommu, iova, PAGE_SIZE);
> > -		vfio_unpin_page_external(dma, iova, do_accounting);
> > +		vfio_unpin_page_external(dma, iova, do_accounting, false, 0);
> >  		phys_pfn[j] = 0;
> >  	}
> >  pin_done:
> > @@ -612,7 +707,8 @@ static int vfio_iommu_type1_unpin_pages(void *iommu_data,
> >  		dma = vfio_find_dma(iommu, iova, PAGE_SIZE);
> >  		if (!dma)
> >  			goto unpin_exit;
> > -		vfio_unpin_page_external(dma, iova, do_accounting);
> > +		vfio_unpin_page_external(dma, iova, do_accounting,
> > +					 iommu->dirty_page_tracking, PAGE_SIZE);
> >  	}
> >  
> >  unpin_exit:
> > @@ -800,6 +896,7 @@ static void vfio_remove_dma(struct vfio_iommu *iommu, struct vfio_dma *dma)
> >  	vfio_unmap_unpin(iommu, dma, true);
> >  	vfio_unlink_dma(iommu, dma);
> >  	put_task_struct(dma->task);
> > +	kfree(dma->bitmap);
> >  	kfree(dma);
> >  	iommu->dma_avail++;
> >  }
> > @@ -830,6 +927,54 @@ static unsigned long vfio_pgsize_bitmap(struct vfio_iommu *iommu)
> >  	return bitmap;
> >  }
> >  
> > +static int vfio_iova_dirty_bitmap(struct vfio_iommu *iommu, dma_addr_t iova,
> > +				  size_t size, uint64_t pgsize,
> > +				  unsigned char __user *bitmap)
> > +{
> > +	struct vfio_dma *dma;
> > +	unsigned long pgshift = __ffs(pgsize);
> > +	unsigned int npages, bitmap_size;
> > +
> > +	dma = vfio_find_dma(iommu, iova, 1);
> > +
> > +	if (!dma)
> > +		return -EINVAL;
> > +
> > +	if (dma->iova != iova || dma->size != size)
> > +		return -EINVAL;
> > +
> > +	npages = dma->size >> pgshift;
> > +	bitmap_size = dirty_bitmap_bytes(npages);
> > +
> > +	/* mark all pages dirty if all pages are pinned and mapped. */
> > +	if (dma->iommu_mapped)
> > +		bitmap_set(dma->bitmap, 0, npages);
> > +
> > +	if (dma->bitmap) {
> > +		if (copy_to_user((void __user *)bitmap, dma->bitmap,
> > +				 bitmap_size))
> > +			return -EFAULT;
> > +
> > +		memset(dma->bitmap, 0, bitmap_size);
> > +	}
> > +	return 0;
> > +}
> > +
> > +static int verify_bitmap_size(unsigned long npages, unsigned long bitmap_size)
> > +{
> > +	long bsize;
> > +
> > +	if (!bitmap_size || bitmap_size > SIZE_MAX)
> > +		return -EINVAL;
> > +
> > +	bsize = dirty_bitmap_bytes(npages);
> > +
> > +	if (bitmap_size < bsize)
> > +		return -EINVAL;
> > +
> > +	return 0;
> > +}
> > +
> >  static int vfio_dma_do_unmap(struct vfio_iommu *iommu,
> >  			     struct vfio_iommu_type1_dma_unmap *unmap)
> >  {
> > @@ -2277,6 +2422,92 @@ static long vfio_iommu_type1_ioctl(void *iommu_data,
> >  
> >  		return copy_to_user((void __user *)arg, &unmap, minsz) ?
> >  			-EFAULT : 0;
> > +	} else if (cmd == VFIO_IOMMU_DIRTY_PAGES) {
> > +		struct vfio_iommu_type1_dirty_bitmap dirty;
> > +		uint32_t mask = VFIO_IOMMU_DIRTY_PAGES_FLAG_START |
> > +				VFIO_IOMMU_DIRTY_PAGES_FLAG_STOP |
> > +				VFIO_IOMMU_DIRTY_PAGES_FLAG_GET_BITMAP;
> > +		int ret;
> > +
> > +		if (!iommu->v2)
> > +			return -EACCES;
> > +
> > +		minsz = offsetofend(struct vfio_iommu_type1_dirty_bitmap,
> > +				    flags);
> > +
> > +		if (copy_from_user(&dirty, (void __user *)arg, minsz))
> > +			return -EFAULT;
> > +
> > +		if (dirty.argsz < minsz || dirty.flags & ~mask)
> > +			return -EINVAL;
> > +
> > +		/* only one flag should be set at a time */
> > +		if (__ffs(dirty.flags) != __fls(dirty.flags))
> > +			return -EINVAL;  
> 
> It seems a bit odd to use a set of ORable flags when only one can be set
> at a time.

Is it really?  It might in the future be true that there are some
combination of flags that are valid, but for the currently defined
flags, they're mutually exclusive.  There's no combination of START |
STOP | GET that makes sense.  Don't read into the current
implementation that this is fixed in the API except as it relates to
the currently defined flags.  Thanks,

Alex
 
> > +		if (dirty.flags & VFIO_IOMMU_DIRTY_PAGES_FLAG_START) {
> > +			unsigned long iommu_pgsize =
> > +					1 << __ffs(vfio_pgsize_bitmap(iommu));
> > +
> > +			mutex_lock(&iommu->lock);
> > +			ret = vfio_dma_all_bitmap_alloc(iommu, iommu_pgsize);
> > +			if (!ret)
> > +				iommu->dirty_page_tracking = true;
> > +			mutex_unlock(&iommu->lock);
> > +			return ret;
> > +		} else if (dirty.flags & VFIO_IOMMU_DIRTY_PAGES_FLAG_STOP) {
> > +			mutex_lock(&iommu->lock);
> > +			if (iommu->dirty_page_tracking) {
> > +				iommu->dirty_page_tracking = false;
> > +				vfio_dma_all_bitmap_free(iommu);
> > +			}
> > +			mutex_unlock(&iommu->lock);
> > +			return 0;
> > +		} else if (dirty.flags &
> > +				 VFIO_IOMMU_DIRTY_PAGES_FLAG_GET_BITMAP) {
> > +			struct vfio_iommu_type1_dirty_bitmap_get range;
> > +			unsigned long pgshift;
> > +			size_t data_size = dirty.argsz - minsz;
> > +			uint64_t iommu_pgsize =
> > +					 1 << __ffs(vfio_pgsize_bitmap(iommu));
> > +
> > +			if (!data_size || data_size < sizeof(range))
> > +				return -EINVAL;
> > +
> > +			if (copy_from_user(&range, (void __user *)(arg + minsz),
> > +					   sizeof(range)))
> > +				return -EFAULT;
> > +
> > +			// allow only min supported pgsize
> > +			if (range.pgsize != iommu_pgsize)
> > +				return -EINVAL;
> > +			if (range.iova & (iommu_pgsize - 1))
> > +				return -EINVAL;
> > +			if (!range.size || range.size & (iommu_pgsize - 1))
> > +				return -EINVAL;
> > +			if (range.iova + range.size < range.iova)
> > +				return -EINVAL;
> > +			if (!access_ok((void __user *)range.bitmap,
> > +				       range.bitmap_size))
> > +				return -EINVAL;
> > +
> > +			pgshift = __ffs(range.pgsize);
> > +			ret = verify_bitmap_size(range.size >> pgshift,
> > +						 range.bitmap_size);
> > +			if (ret)
> > +				return ret;
> > +
> > +			mutex_lock(&iommu->lock);
> > +			if (iommu->dirty_page_tracking)
> > +				ret = vfio_iova_dirty_bitmap(iommu, range.iova,
> > +					 range.size, range.pgsize,
> > +					 (unsigned char __user *)range.bitmap);
> > +			else
> > +				ret = -EINVAL;
> > +			mutex_unlock(&iommu->lock);
> > +
> > +			return ret;
> > +		}
> >  	}
> >  
> >  	return -ENOTTY;
> > -- 
> > 2.7.0
> >   
> --
> Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK