Re: [PATCH v3 11/33] drm/gpusvm: Add a DMA-mapping accounting callback

[Matthew Brost <matthew.brost@intel.com>]

On Tue, Nov 03, 2026 at 08:10:45PM -0800, Niranjana Vishwanathapura wrote:
> On Tue, Nov 03, 2026 at 07:41:06PM -0800, Niranjana Vishwanathapura wrote:
> > On Fri, Jul 10, 2026 at 07:55:57PM -0700, Matthew Brost wrote:
> > > From: Thomas Hellström <thomas.hellstrom@linux.intel.com>
> > > 
> > > Drivers that use the GPU SVM core to DMA-map system memory for GPU
> > > access may want to keep track of how many pages they have mapped, for
> > > example to expose statistics or to detect leaks. Doing this accounting
> > > in the driver around drm_gpusvm_get_pages() / drm_gpusvm_unmap_pages()
> > > is error prone: the number, order and kind of the dma_addr[] entries can
> > > change between map and unmap (migration, partial unmaps, the iova vs
> > > non-iova paths), which makes symmetric accounting hard to get right.
> > > 
> > > Add an optional @dma_map_account callback to struct drm_gpusvm_ops and
> > > invoke it once per &drm_pagemap_addr entry at the exact points where the
> > > entry is DMA-mapped (sign == +1) in drm_gpusvm_get_pages() and unmapped
> > > (sign == -1) in __drm_gpusvm_unmap_pages(). Since the map error path and
> > > every unmap/free path funnel through __drm_gpusvm_unmap_pages() for the
> > > entries that were actually mapped, the accounting is symmetric by
> > > construction. The callback receives the full &drm_pagemap_addr so the
> > > driver can use the order and the proto field to distinguish system
> > > memory mappings from device interconnect mappings.
> > > 
> > > The callback must also be usable by the core drm_gpusvm_pages-only API
> > > (mm == NULL), as used e.g. for userptr-style mappings. Relax
> > > drm_gpusvm_init() to allow such users to pass a restricted @ops that
> > > only implements the page-level hooks; the full-SVM hooks (@invalidate)
> > > and the chunk configuration must still be unset in that mode.
> > > 
> > > Assisted-by: GitHub_Copilot:claude-opus-4.8
> > > Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
> > 
> > Patches 11 and 12 can be spinned out as a separate patch series
> > (for fast tracking).
> > 
> > LGTM.
> > Reviewed-by: Niranjana Vishwanathapura <niranjana.vishwanathapura@intel.com>
> 
> One other point below...
> 
> > 
> > > ---
> > > drivers/gpu/drm/drm_gpusvm.c | 17 +++++++++++++++--
> > > include/drm/drm_gpusvm.h     | 19 +++++++++++++++++++
> > > 2 files changed, 34 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/drivers/gpu/drm/drm_gpusvm.c b/drivers/gpu/drm/drm_gpusvm.c
> > > index fcfe635bc195..512f52471419 100644
> > > --- a/drivers/gpu/drm/drm_gpusvm.c
> > > +++ b/drivers/gpu/drm/drm_gpusvm.c
> > > @@ -474,8 +474,15 @@ int drm_gpusvm_init(struct drm_gpusvm *gpusvm,
> > > 			return -EINVAL;
> > > 		mmgrab(mm);
> > > 	} else {
> > > -		/* No full SVM mode, only core drm_gpusvm_pages API. */
> > > -		if (ops || num_chunks || mm_range || notifier_size)
> > > +		/*
> > > +		 * No full SVM mode, only core drm_gpusvm_pages API. A
> > > +		 * restricted @ops that only implements the page-level hooks
> > > +		 * (e.g. @dma_map_account) is allowed; the full-SVM hooks must
> > > +		 * not be set.
> > > +		 */
> > > +		if (num_chunks || mm_range || notifier_size)
> > > +			return -EINVAL;
> > > +		if (ops && ops->invalidate)
> > > 			return -EINVAL;
> > > 	}
> > > 
> > > @@ -1246,6 +1253,8 @@ static void __drm_gpusvm_unmap_pages(struct drm_gpusvm *gpusvm,
> > > 			else if (dpagemap && dpagemap->ops->device_unmap)
> > > 				dpagemap->ops->device_unmap(dpagemap,
> > > 							    dev, addr);
> > > +			if (gpusvm->ops && gpusvm->ops->dma_map_account)
> > > +				gpusvm->ops->dma_map_account(gpusvm, addr, -1);
> 
> In the latest code, there is use_iova path and unamp there doesn't seem to
> come here for that case. Something to take care of during rebase.
> 

Yep. I have this fixed also because of inline mappings some further
adjustments are needed.

Posting now with this fixed.

Matt

> Niranjana
> 
> > > 			i += 1 << addr->order;
> > > 		}
> > > 
> > > @@ -1654,6 +1663,10 @@ int drm_gpusvm_get_pages(struct drm_gpusvm *gpusvm,
> > > 				(addr, DRM_INTERCONNECT_SYSTEM, order,
> > > 				 dma_dir);
> > > 		}
> > > +		if (gpusvm->ops && gpusvm->ops->dma_map_account)
> > > +			gpusvm->ops->dma_map_account(gpusvm,
> > > +						     &svm_pages->dma_addr[j],
> > > +						     1);
> > > 		i += 1 << order;
> > > 		num_dma_mapped = i;
> > > 		flags.has_dma_mapping = true;
> > > diff --git a/include/drm/drm_gpusvm.h b/include/drm/drm_gpusvm.h
> > > index b7d987bf76aa..36f35816a569 100644
> > > --- a/include/drm/drm_gpusvm.h
> > > +++ b/include/drm/drm_gpusvm.h
> > > @@ -75,6 +75,25 @@ struct drm_gpusvm_ops {
> > > 	void (*invalidate)(struct drm_gpusvm *gpusvm,
> > > 			   struct drm_gpusvm_notifier *notifier,
> > > 			   const struct mmu_notifier_range *mmu_range);
> > > +
> > > +	/**
> > > +	 * @dma_map_account: Account a DMA-mapping change (optional)
> > > +	 * @gpusvm: Pointer to the GPU SVM
> > > +	 * @addr: The address descriptor of the chunk being (un)mapped
> > > +	 * @sign: +1 when @addr has just been DMA-mapped, -1 when it is being
> > > +	 *        unmapped
> > > +	 *
> > > +	 * Called once per &drm_pagemap_addr entry, when the entry is
> > > +	 * DMA-mapped by drm_gpusvm_get_pages() (@sign == +1) and when it is
> > > +	 * unmapped (@sign == -1), so the driver can keep symmetric accounting
> > > +	 * of the pages it has mapped for GPU access. The @addr->proto field
> > > +	 * can be used to distinguish system-memory mappings from device
> > > +	 * interconnect mappings. May be provided in both full SVM mode and the
> > > +	 * core drm_gpusvm_pages-only mode.
> > > +	 */
> > > +	void (*dma_map_account)(struct drm_gpusvm *gpusvm,
> > > +				const struct drm_pagemap_addr *addr,
> > > +				int sign);
> > > };
> > > 
> > > /**
> > > -- 
> > > 2.34.1
> > >