On Wed, Nov 04, 2026 at 04:49:01PM -0800, Niranjana Vishwanathapura wrote:
> On Wed, Nov 04, 2026 at 01:52:27PM -0800, Matthew Brost wrote:
> > From: Thomas Hellström <[email protected]>
> >
> > 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: LLM
> > Signed-off-by: Thomas Hellström <[email protected]>
> > Signed-off-by: Matthew Brost <[email protected]>
> > Reviewed-by: Niranjana Vishwanathapura <[email protected]>
> > ---
> > drivers/gpu/drm/drm_gpusvm.c | 40 ++++++++++++++++++++++++++++--------
> > include/drm/drm_gpusvm.h | 19 +++++++++++++++++
> > 2 files changed, 50 insertions(+), 9 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/drm_gpusvm.c b/drivers/gpu/drm/drm_gpusvm.c
> > index 03dbe304e4b8..5ef9d7233491 100644
> > --- a/drivers/gpu/drm/drm_gpusvm.c
> > +++ b/drivers/gpu/drm/drm_gpusvm.c
> > @@ -503,8 +503,15 @@ 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;
>
> Other than 'invalidate' here, should we also check for other ops like
> range_alloc, range_free etc?
>
Yes. Let me fix that.
Matt
> Niranjana
>
> > }
> >
> > @@ -1240,9 +1247,12 @@ static void __drm_gpusvm_unmap_pages(struct
> > drm_gpusvm *gpusvm,
> > struct drm_gpusvm_pages_flags flags = {
> > .__flags = svm_pages->flags.__flags,
> > };
> > + bool contiguous;
> > const struct drm_pagemap_addr *addrs =
> > - drm_gpusvm_pages_first_dma(svm_pages, NULL);
> > + drm_gpusvm_pages_first_dma(svm_pages, &contiguous);
> > bool use_iova = dma_use_iova(&svm_pages->state);
> > + bool needs_account = gpusvm->ops &&
> > + gpusvm->ops->dma_map_account;
> >
> > /*
> > * IOVA is reserved for the whole range but only the linked
> > @@ -1260,14 +1270,18 @@ static void __drm_gpusvm_unmap_pages(struct
> > drm_gpusvm *gpusvm,
> >
> > /*
> > * With IOVA and no device page the unlink above tore every
> > - * entry down, and that is also when the range may be folded
> > - * to one entry, which must not be walked per entry. dpagemap
> > - * is set before the first device_map(), so it is also right
> > - * on the error path, where the flags are not published yet.
> > + * entry down, but the per-entry walk is still needed when the
> > + * driver accounts the mappings. A folded (inline) mapping has
> > + * a single entry describing the whole range, so it must be
> > + * re-read for every iteration instead of indexed by @j.
> > + * dpagemap is set before the first device_map(), so it is also
> > + * right on the error path, where the flags are not published
> > + * yet.
> > */
> > for (i = 0, j = 0;
> > - (!use_iova || dpagemap) && i < npages; j++) {
> > - const struct drm_pagemap_addr *addr = &addrs[j];
> > + (!use_iova || dpagemap || needs_account) && i < npages;
> > j++) {
> > + const struct drm_pagemap_addr *addr =
> > + contiguous ? &addrs[0] : &addrs[j];
> >
> > if (addr->proto == DRM_INTERCONNECT_SYSTEM) {
> > /*
> > @@ -1283,6 +1297,10 @@ 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 (needs_account)
> > + gpusvm->ops->dma_map_account(gpusvm, addr, -1);
> > +
> > i += 1 << addr->order;
> > }
> >
> > @@ -1705,6 +1723,10 @@ static int drm_gpusvm_dma_map_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 4d31c6bba745..637c19f7169f 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
> >
