On 22.10.2025 10:05, Adrián Larumbe wrote:
> On 22.10.2025 05:45, Akash Goel wrote:
> >
> >
> > On 10/21/25 18:39, Adrián Larumbe wrote:
> > > Hi Akash,
> > >
> > > On 21.10.2025 15:32, Akash Goel wrote:
> > > >
> > > >
> > > > On 10/19/25 04:19, Adrián Larumbe wrote:
> > > > > Commit 33729a5fc0ca ("iommu/io-pgtable-arm: Remove split on unmap
> > > > > behavior") did away with the treatment of partial unmaps of huge
> > > > > IOPTEs.
> > > > >
> > > >
> > > > Sorry have a doubt.
> > > >
> > > > Corresponding to the commit 33729a5fc0ca, can we now remove the code to
> > > > pre-allocate L3 page table pages i.e. 'op_ctx->rsvd_page_tables.pages'
> > > > inside
> > > > panthor_vm_prepare_unmap_op_ctx() ?.
> > > >
> > > > > In the case of Panthor, that means an attempt to run a VM_BIND unmap
> > > > > operation on a memory region whose start address and size aren't 2MiB
> > > > > aligned, in the event it intersects with a huge page, would lead to
> > > > > ARM
> > > > > IOMMU management code to fail and a warning being raised.
> > > > >
> > > > > Presently, and for lack of a better alternative, it's best to have
> > > > > Panthor handle partial unmaps at the driver level, by unmapping entire
> > > > > huge pages and remapping the difference between them and the requested
> > > > > unmap region.
> > > > >
> > > > > This could change in the future when the VM_BIND uAPI is expanded to
> > > > > enforce huge page alignment and map/unmap operational constraints that
> > > > > render this code unnecessary.
> > > > >
> > > > > Signed-off-by: Adrián Larumbe <[email protected]>
> > > > > ---
> > > > > drivers/gpu/drm/panthor/panthor_mmu.c | 129
> > > > > +++++++++++++++++++++++++-
> > > > > 1 file changed, 126 insertions(+), 3 deletions(-)
> > > > >
> > > > > diff --git a/drivers/gpu/drm/panthor/panthor_mmu.c
> > > > > b/drivers/gpu/drm/panthor/panthor_mmu.c
> > > > > index 2d041a2e75e9..f9d200e57c04 100644
> > > > > --- a/drivers/gpu/drm/panthor/panthor_mmu.c
> > > > > +++ b/drivers/gpu/drm/panthor/panthor_mmu.c
> > > > > @@ -2093,6 +2093,98 @@ static int panthor_gpuva_sm_step_map(struct
> > > > > drm_gpuva_op *op, void *priv)
> > > > > return 0;
> > > > > }
> > > > > +static bool
> > > > > +is_huge_page_partial_unmap(const struct panthor_vma *unmap_vma,
> > > > > + const struct drm_gpuva_op_map *op,
> > > > > + u64 unmap_start, u64 unmap_range,
> > > > > + u64 sz2m_prev, u64 sz2m_next)
> > > > > +{
> > > > > + size_t pgcount, pgsize;
> > > > > + const struct page *pg;
> > > > > + pgoff_t bo_offset;
> > > > > +
> > > > > + if (op->va.addr < unmap_vma->base.va.addr) {
> > > >
> > > >
> > > > Sorry, another doubt.
> > > >
> > > > Will this condition ever be true ?
> > > >
> > > > For 'op->remap.prev', 'op->va.addr' will always be equal to
> > > > 'unmap_vma->base.va.addr'.
> > >
> > > I believe it will always be less than that.
> >
> >
> > Thanks Adrian for having a look.
> >
> > static int panthor_gpuva_sm_step_remap(struct drm_gpuva_op *op,
> > {
> > struct panthor_vma *unmap_vma = container_of(op->remap.unmap->va, struct
> > panthor_vma, base);
> >
> >
> > IIUC, the 'unmap_vma' passed to panthor_gpuva_sm_step_remap() will always
> > cover the entire VA range of 'drm_gpuva'.
> > That's why drm_gpuva_op_remap_to_unmap_range() is called to know the exact
> > range to be unmapped.
> >
> > In __drm_gpuvm_sm_unmap() and __drm_gpuvm_sm_map(), you can see this,
> >
> > struct drm_gpuva_op_unmap u = { .va = va };
> >
> >
> > > What will be equal to unmap_vma->base.va.addr is op->remap.prev->va.addr +
> > op->remap.prev->va.range
> >
> >
> > I think op->remap.prev->va.addr + op->remap.prev->va.range will be equal to
> > 'unmap_start' after the call to drm_gpuva_op_remap_to_unmap_range().
> >
> > Sorry I may have again misunderstood the code.
>
> I had a second look __drm_gpuvm_sm_unmap() and you're right. I should've said
> it's always
> the case that op->va.addr < unmap_start inside is_huge_page_partial_unmap.
>
> This is a bug and it makes me wonder why when I ran some tests, the unmap
> intervals
> I got seemed fine. I'll go try again and also test Boris' implementation
> suggestion.
Turns out the reason the code worked was all the testing I've done is
over previous mappings that were always a multiple of 2MiB in length, so
even when the op in question was previous to the original 'unmap' one
and 'if (op->va.addr < unmap_vma->base.va.addr) evaluated to false', the
ending address of next.va would also belong to a 2MiB huge page, so the
condition would still hold.
This is a glaring bug and would show up when the end address of
remap->next.va doesn't belong to a huge page. This means I need to
provide a more detailed testing plan for the next revision.
> > Please can you check.
> >
> > Best regards
> > Akash
> >
> >
> > > > And for 'op->remap.next', 'op->va.addr' will always be greater than
> > > > 'unmap_vma->base.va.addr'.
> > >
> > > Yes, I believe so.
> > >
> > > > Please can you clarify.
> > > >
> > > > Best regards
> > > > Akash
> > > >
> > > >
> > > > > + bo_offset = unmap_start - unmap_vma->base.va.addr +
> > > > > unmap_vma->base.gem.offset;
> > > > > + sz2m_prev = ALIGN_DOWN(unmap_start, SZ_2M);
> > > > > + sz2m_next = ALIGN(unmap_start + 1, SZ_2M);
> > > > > + pgsize = get_pgsize(unmap_start, unmap_range, &pgcount);
> > > > > +
> > > > > + } else {
> > > > > + bo_offset = ((unmap_start + unmap_range - 1) -
> > > > > unmap_vma->base.va.addr)
> > > > > + + unmap_vma->base.gem.offset;
> > > > > + sz2m_prev = ALIGN_DOWN(unmap_start + unmap_range - 1,
> > > > > SZ_2M);
> > > > > + sz2m_next = ALIGN(unmap_start + unmap_range, SZ_2M);
> > > > > + pgsize = get_pgsize(sz2m_prev, unmap_start +
> > > > > unmap_range - sz2m_prev, &pgcount);
> > > > > + }
> > > > > +
> > > > > + pg =
> > > > > to_panthor_bo(unmap_vma->base.gem.obj)->base.pages[bo_offset >>
> > > > > PAGE_SHIFT];
> > > > > +
> > > > > + if (pgsize == SZ_4K && folio_order(page_folio(pg)) == PMD_ORDER
> > > > > &&
> > > > > + unmap_vma->base.va.addr <= sz2m_prev &&
> > > > > unmap_vma->base.va.addr +
> > > > > + unmap_vma->base.va.range >= sz2m_next)
> > > > > + return true;
> > > > > +
> > > > > + return false;
> > > > > +}
> > > > > +
> > > > > +struct remap_params {
> > > > > + u64 prev_unmap_start, prev_unmap_range;
> > > > > + u64 prev_remap_start, prev_remap_range;
> > > > > + u64 next_unmap_start, next_unmap_range;
> > > > > + u64 next_remap_start, next_remap_range;
> > > > > + u64 unmap_start, unmap_range;
> > > > > +};
> > > > > +
> > > > > +static struct remap_params
> > > > > +get_map_unmap_intervals(const struct drm_gpuva_op_remap *op,
> > > > > + const struct panthor_vma *unmap_vma)
> > > > > +{
> > > > > + u64 unmap_start, unmap_range, sz2m_prev, sz2m_next;
> > > > > + struct remap_params params = {0};
> > > > > +
> > > > > + drm_gpuva_op_remap_to_unmap_range(op, &unmap_start,
> > > > > &unmap_range);
> > > > > +
> > > > > + if (op->prev) {
> > > > > + sz2m_prev = ALIGN_DOWN(unmap_start, SZ_2M);
> > > > > + sz2m_next = ALIGN(unmap_start + 1, SZ_2M);
> > > > > +
> > > > > + if (is_huge_page_partial_unmap(unmap_vma, op->prev,
> > > > > unmap_start,
> > > > > + unmap_range, sz2m_prev,
> > > > > sz2m_next)) {
> > > > > + params.prev_unmap_start = sz2m_prev;
> > > > > + params.prev_unmap_range = SZ_2M;
> > > > > + params.prev_remap_start = sz2m_prev;
> > > > > + params.prev_remap_range = unmap_start & (SZ_2M
> > > > > - 1);
> > > > > +
> > > > > + u64 diff = min(sz2m_next - unmap_start,
> > > > > unmap_range);
> > > > > +
> > > > > + unmap_range -= diff;
> > > > > + unmap_start += diff;
> > > > > + }
> > > > > + }
> > > > > +
> > > > > + if (op->next) {
> > > > > + sz2m_prev = ALIGN_DOWN(unmap_start + unmap_range - 1,
> > > > > SZ_2M);
> > > > > + sz2m_next = ALIGN(unmap_start + unmap_range, SZ_2M);
> > > > > +
> > > > > + if (is_huge_page_partial_unmap(unmap_vma, op->next,
> > > > > unmap_start,
> > > > > + unmap_range, sz2m_prev,
> > > > > sz2m_next)) {
> > > > > + if (unmap_range) {
> > > > > + params.next_unmap_start = sz2m_prev;
> > > > > + params.next_unmap_range = SZ_2M;
> > > > > + unmap_range -= op->next->va.addr &
> > > > > (SZ_2M - 1);
> > > > > + }
> > > > > +
> > > > > + params.next_remap_start = op->next->va.addr;
> > > > > + params.next_remap_range = SZ_2M -
> > > > > (op->next->va.addr & (SZ_2M - 1));
> > > > > + }
> > > > > + }
> > > > > +
> > > > > + params.unmap_start = unmap_start;
> > > > > + params.unmap_range = unmap_range;
> > > > > +
> > > > > + return params;
> > > > > +}
> > > > > +
> > > > > static int panthor_gpuva_sm_step_remap(struct drm_gpuva_op *op,
> > > > > void *priv)
> > > > > {
> > > > > @@ -2100,20 +2192,51 @@ static int panthor_gpuva_sm_step_remap(struct
> > > > > drm_gpuva_op *op,
> > > > > struct panthor_vm *vm = priv;
> > > > > struct panthor_vm_op_ctx *op_ctx = vm->op_ctx;
> > > > > struct panthor_vma *prev_vma = NULL, *next_vma = NULL;
> > > > > - u64 unmap_start, unmap_range;
> > > > > + struct remap_params params;
> > > > > int ret;
> > > > > - drm_gpuva_op_remap_to_unmap_range(&op->remap, &unmap_start,
> > > > > &unmap_range);
> > > > > - ret = panthor_vm_unmap_pages(vm, unmap_start, unmap_range);
> > > > > + /*
> > > > > + * ARM IOMMU page table management code disallows partial
> > > > > unmaps of huge pages,
> > > > > + * so when a partial unmap is requested, we must first unmap
> > > > > the entire huge
> > > > > + * page and then remap the difference between the huge page
> > > > > minus the requested
> > > > > + * unmap region. Calculating the right offsets and ranges for
> > > > > the different unmap
> > > > > + * and map operations is the responsibility of the following
> > > > > function.
> > > > > + */
> > > > > + params = get_map_unmap_intervals(&op->remap, unmap_vma);
> > > > > +
> > > > > + ret = panthor_vm_unmap_pages(vm, params.unmap_start,
> > > > > params.unmap_range);
> > > > > if (ret)
> > > > > return ret;
> > > > > if (op->remap.prev) {
> > > > > + ret = panthor_vm_unmap_pages(vm,
> > > > > params.prev_unmap_start,
> > > > > + params.prev_unmap_range);
> > > > > + if (ret)
> > > > > + return ret;
> > > > > + ret = panthor_vm_map_pages(vm, params.prev_remap_start,
> > > > > +
> > > > > flags_to_prot(unmap_vma->flags),
> > > > > +
> > > > > to_drm_gem_shmem_obj(op->remap.prev->gem.obj)->sgt,
> > > > > + op->remap.prev->gem.offset,
> > > > > params.prev_remap_range);
> > > > > + if (ret)
> > > > > + return ret;
> > > > > +
> > > > > prev_vma = panthor_vm_op_ctx_get_vma(op_ctx);
> > > > > panthor_vma_init(prev_vma, unmap_vma->flags);
> > > > > }
> > > > > if (op->remap.next) {
> > > > > + ret = panthor_vm_unmap_pages(vm,
> > > > > params.next_unmap_start,
> > > > > + params.next_unmap_range);
> > > > > + if (ret)
> > > > > + return ret;
> > > > > +
> > > > > + ret = panthor_vm_map_pages(vm, params.next_remap_start,
> > > > > +
> > > > > flags_to_prot(unmap_vma->flags),
> > > > > +
> > > > > to_drm_gem_shmem_obj(op->remap.next->gem.obj)->sgt,
> > > > > + op->remap.next->gem.offset,
> > > > > params.next_remap_range);
> > > > > + if (ret)
> > > > > + return ret;
> > > > > +
> > > > > next_vma = panthor_vm_op_ctx_get_vma(op_ctx);
> > > > > panthor_vma_init(next_vma, unmap_vma->flags);
> > > > > }
> > > > >
> > > > > base-commit: 7fb19ea1ec6aa85c75905b1fd732d50801e7fb28
> > > > > prerequisite-patch-id: 3b0f61bfc22a616a205ff7c15d546d2049fd53de
> > >
> > > Adrian Larumbe
