[PATCH v4 1/7] drm/panthor: Add support for atomic page table updates
Caterina Shablia
caterina.shablia at collabora.com
Tue Jul 15 15:08:09 UTC 2025
El viernes, 11 de julio de 2025 15:30:21 (hora de verano de Europa central),
Steven Price escribió:
> On 07/07/2025 18:04, Caterina Shablia wrote:
> > From: Boris Brezillon <boris.brezillon at collabora.com>
> >
> > Move the lock/flush_mem operations around the gpuvm_sm_map() calls so
> > we can implement true atomic page updates, where any access in the
> > locked range done by the GPU has to wait for the page table updates
> > to land before proceeding.
> >
> > This is needed for vkQueueBindSparse(), so we can replace the dummy
> > page mapped over the entire object by actual BO backed pages in an atomic
> > way.
> >
> > Signed-off-by: Boris Brezillon <boris.brezillon at collabora.com>
> > Signed-off-by: Caterina Shablia <caterina.shablia at collabora.com>
> > ---
> >
> > drivers/gpu/drm/panthor/panthor_mmu.c | 65 +++++++++++++++++++++++++--
> > 1 file changed, 62 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/panthor/panthor_mmu.c
> > b/drivers/gpu/drm/panthor/panthor_mmu.c index b39ea6acc6a9..9caaba03c5eb
> > 100644
> > --- a/drivers/gpu/drm/panthor/panthor_mmu.c
> > +++ b/drivers/gpu/drm/panthor/panthor_mmu.c
> > @@ -387,6 +387,15 @@ struct panthor_vm {
> >
> > * flagged as faulty as a result.
> > */
> >
> > bool unhandled_fault;
> >
> > +
> > + /** @locked_region: Information about the currently locked region
> > currently. */ + struct {
> > + /** @locked_region.start: Start of the locked region.
*/
> > + u64 start;
> > +
> > + /** @locked_region.size: Size of the locked region. */
> > + u64 size;
> > + } locked_region;
> >
> > };
> >
> > /**
> >
> > @@ -775,6 +784,10 @@ int panthor_vm_active(struct panthor_vm *vm)
> >
> > }
> >
> > ret = panthor_mmu_as_enable(vm->ptdev, vm->as.id, transtab,
transcfg,
> > vm->memattr);>
> > + if (!ret && vm->locked_region.size) {
> > + lock_region(ptdev, vm->as.id, vm->locked_region.start,
> > vm->locked_region.size); + ret = wait_ready(ptdev, vm-
>as.id);
> > + }
>
> Do we need to do this? It seems odd to restore a MMU context and
> immediately set a lock region. Is there a good reason we can't just
> WARN_ON if there's a lock region set in panthor_vm_idle()?
So IIUC, when things are otherwise idle and we do a vm_bind, the vm will be
inactive, in which case we're not going to poke the mmu to inform it of the
locked region, because it literally is not aware of this vm. Now if in the
meanwhile something submits a job and activates the vm, we need to inform the
mmu of the locked region, as vm_bind job might still be going on. I don't see
why panthor_vm_idle while a region is locked would be a problem? That can
arise e.g. when a job completes but there's a concurrent vm_bind going on?
>
> I think we need to briefly take vm->op_lock to ensure synchronisation
> but that doesn't seem a big issue. Or perhaps there's a good reason that
> I'm missing?
I think you're right, all other accesses to locked_region are guarded by
op_lock. GPU job submit poke vm_active concurrently with vm_bind jobs doing
region {,un}locks.
>
> > out_make_active:
> > if (!ret) {
> >
> > @@ -902,6 +915,9 @@ static int panthor_vm_unmap_pages(struct panthor_vm
> > *vm, u64 iova, u64 size)>
> > struct io_pgtable_ops *ops = vm->pgtbl_ops;
> > u64 offset = 0;
> >
> > + drm_WARN_ON(&ptdev->base,
> > + (iova < vm->locked_region.start) ||
> > + (iova + size > vm->locked_region.start + vm-
>locked_region.size));
> >
> > drm_dbg(&ptdev->base, "unmap: as=%d, iova=%llx, len=%llx", vm-
>as.id,
> > iova, size);
> >
> > while (offset < size) {
> >
> > @@ -915,13 +931,12 @@ static int panthor_vm_unmap_pages(struct panthor_vm
> > *vm, u64 iova, u64 size)>
> > iova + offset + unmapped_sz,
> > iova + offset + pgsize * pgcount,
> > iova, iova + size);
> >
> > - panthor_vm_flush_range(vm, iova, offset +
unmapped_sz);
> >
> > return -EINVAL;
> >
> > }
> > offset += unmapped_sz;
> >
> > }
> >
> > - return panthor_vm_flush_range(vm, iova, size);
> > + return 0;
> >
> > }
> >
> > static int
> >
> > @@ -938,6 +953,10 @@ panthor_vm_map_pages(struct panthor_vm *vm, u64 iova,
> > int prot,>
> > if (!size)
> >
> > return 0;
> >
> > + drm_WARN_ON(&ptdev->base,
> > + (iova < vm->locked_region.start) ||
> > + (iova + size > vm->locked_region.start + vm-
>locked_region.size));
> > +
> >
> > for_each_sgtable_dma_sg(sgt, sgl, count) {
> >
> > dma_addr_t paddr = sg_dma_address(sgl);
> > size_t len = sg_dma_len(sgl);
> >
> > @@ -985,7 +1004,7 @@ panthor_vm_map_pages(struct panthor_vm *vm, u64 iova,
> > int prot,>
> > offset = 0;
> >
> > }
> >
> > - return panthor_vm_flush_range(vm, start_iova, iova - start_iova);
> > + return 0;
> >
> > }
> >
> > static int flags_to_prot(u32 flags)
> >
> > @@ -1654,6 +1673,38 @@ static const char *access_type_name(struct
> > panthor_device *ptdev,>
> > }
> >
> > }
> >
> > +static int panthor_vm_lock_region(struct panthor_vm *vm, u64 start, u64
> > size) +{
> > + struct panthor_device *ptdev = vm->ptdev;
> > + int ret = 0;
> > +
> > + mutex_lock(&ptdev->mmu->as.slots_lock);
> > + drm_WARN_ON(&ptdev->base, vm->locked_region.start ||
> > vm->locked_region.size); + vm->locked_region.start = start;
> > + vm->locked_region.size = size;
> > + if (vm->as.id >= 0) {
> > + lock_region(ptdev, vm->as.id, start, size);
> > + ret = wait_ready(ptdev, vm->as.id);
> > + }
> > + mutex_unlock(&ptdev->mmu->as.slots_lock);
> > +
> > + return ret;
> > +}
> > +
> > +static void panthor_vm_unlock_region(struct panthor_vm *vm)
> > +{
> > + struct panthor_device *ptdev = vm->ptdev;
> > +
> > + mutex_lock(&ptdev->mmu->as.slots_lock);
> > + if (vm->as.id >= 0) {
> > + write_cmd(ptdev, vm->as.id, AS_COMMAND_FLUSH_MEM);
> > + drm_WARN_ON(&ptdev->base, wait_ready(ptdev, vm-
>as.id));
> > + }
> > + vm->locked_region.start = 0;
> > + vm->locked_region.size = 0;
> > + mutex_unlock(&ptdev->mmu->as.slots_lock);
> > +}
>
> Do we need to include a drm_dev_enter() somewhere here? I note that
> panthor_vm_flush_range() has one and you've effectively replaced that
> code with the above.
Looks like we should.
>
> Thanks,
> Steve
>
> > +
> >
> > static void panthor_mmu_irq_handler(struct panthor_device *ptdev, u32
> > status) {
> >
> > bool has_unhandled_faults = false;
> >
> > @@ -2179,6 +2230,11 @@ panthor_vm_exec_op(struct panthor_vm *vm, struct
> > panthor_vm_op_ctx *op,>
> > mutex_lock(&vm->op_lock);
> > vm->op_ctx = op;
> >
> > +
> > + ret = panthor_vm_lock_region(vm, op->va.addr, op->va.range);
> > + if (ret)
> > + goto out;
> > +
> >
> > switch (op_type) {
> >
> > case DRM_PANTHOR_VM_BIND_OP_TYPE_MAP:
> > if (vm->unusable) {
> >
> > @@ -2199,6 +2255,9 @@ panthor_vm_exec_op(struct panthor_vm *vm, struct
> > panthor_vm_op_ctx *op,>
> > break;
> >
> > }
> >
> > + panthor_vm_unlock_region(vm);
> > +
> >
> > +out:
> > if (ret && flag_vm_unusable_on_failure)
> >
> > vm->unusable = true;
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