Re: [PATCH 1/2] drm/panthor: Add vm_bind region with kbo range intersection check

["Adrián Larumbe" <adrian.larumbe@collabora.com>]

On 2026-06-17 20:50:03+02:00, Boris Brezillon wrote:
> On Tue, 16 Jun 2026 15:46:43 +0100
> Adrián Larumbe <adrian.larumbe@collabora.com> wrote:
> 
> > When a VM is created, caller has to specify the range of the address space
> > carve-out set aside for mapping kernel BO's. That means vm_bind mappings of
> > UM-exposed BO's should not intersect with that region, but at the moment
> > we're not checking this.
> > 
> > At first, I thought of giving these values to drm_gpuvm_init() through its
> > reserve_{offset, range} arguments, but it turns out that is meant for VM
> > address spans that are not managed through the usual drm_gpuvm split/merge
> > circuit, so I had no choice but to sort of duplicate that functionality in
> > Panthor. That means we also need to keep that interval recorded in the VM.
> > 
> > Signed-off-by: Adrián Larumbe <adrian.larumbe@collabora.com>
> > ---
> >  drivers/gpu/drm/panthor/panthor_mmu.c | 33 +++++++++++++++++++++++++++++++++
> >  1 file changed, 33 insertions(+)
> > 
> > diff --git a/drivers/gpu/drm/panthor/panthor_mmu.c b/drivers/gpu/drm/panthor/panthor_mmu.c
> > index 31cc57029c12..5625f3d34031 100644
> > --- a/drivers/gpu/drm/panthor/panthor_mmu.c
> > +++ b/drivers/gpu/drm/panthor/panthor_mmu.c
> > @@ -301,6 +301,15 @@ struct panthor_vm {
> >  	/** @mm_lock: Lock protecting the @mm field. */
> >  	struct mutex mm_lock;
> >  
> > +	/** @kernel_va: VA-range reserved for kernel BOs. */
> > +	struct {
> > +		/** @kernel_va.start: Start of the VA-range for kernel BOs. */
> > +		u64 start;
> > +
> > +		/** @kernel_va.range: Size of the automatic VA-range for kernel BOs. */
> > +		u64 range;
> > +	} kernel_va;
> 
> We can do with a single user_va_end.
> 
> > +
> >  	/** @kernel_auto_va: Automatic VA-range for kernel BOs. */
> >  	struct {
> >  		/** @kernel_auto_va.start: Start of the automatic VA-range for kernel BOs. */
> > @@ -1309,6 +1318,24 @@ static int panthor_vm_op_ctx_prealloc_pts(struct panthor_vm_op_ctx *op_ctx)
> >  	return 0;
> >  }
> >  
> > +static bool
> > +panthor_vm_is_kernel_address(struct panthor_vm *vm,
> > +			     const struct drm_panthor_vm_bind_op *op)
> 
> Rather than checking if the VA is not in the kernel range, I'd check
> that the VA is in the user range, since that's what we want to enforce,
> and if we ever decide to carve out extra sections above the user-range
> that the UMD is not supposed to access, we would still catch invalid
> map/unmap ops.
> 
> > +{
> > +	u32 op_type = op->flags & DRM_PANTHOR_VM_BIND_OP_TYPE_MASK;
> > +	u64 end, kstart, krange, kend;
> > +
> > +	if (op_type == DRM_PANTHOR_VM_BIND_OP_TYPE_SYNC_ONLY)
> > +		return false;
> 
> IIRC, we force op->va and op->size to be zero in that case[1], so no
> need for this extra check IMHO.
> 
> > +
> > +	end = op->va + op->size;
> > +	kstart = vm->kernel_va.start;
> > +	krange = vm->kernel_va.range;
> > +	kend = kstart + krange;
> > +
> > +	return krange && op->va < kend && kstart < end;
> 
> A single
> 
> 	op->va + op->size <= vm->user_va_end;
> 
> would do, at which point I'm not too sure adding a helper makes sense.

I'll do this for v2.

> > +}
> > +
> >  #define PANTHOR_VM_BIND_OP_MAP_FLAGS \
> >  	(DRM_PANTHOR_VM_BIND_OP_MAP_READONLY | \
> >  	 DRM_PANTHOR_VM_BIND_OP_MAP_NOEXEC | \
> > @@ -2891,6 +2918,8 @@ panthor_vm_create(struct panthor_device *ptdev, bool for_mcu,
> >  	} else {
> >  		min_va = 0;
> >  		va_range = full_va_range;
> > +		vm->kernel_va.start = kernel_va_start;
> > +		vm->kernel_va.range = kernel_va_size;
> >  	}
> >  
> >  	mutex_init(&vm->mm_lock);
> > @@ -2981,6 +3010,10 @@ panthor_vm_bind_prepare_op_ctx(struct drm_file *file,
> >  	if (!IS_ALIGNED(op->va | op->size | op->bo_offset, vm_pgsz))
> >  		return -EINVAL;
> >  
> > +	/* We don't allow mappings that intersect with kbo's reserved range */
> > +	if (panthor_vm_is_kernel_address(vm, op))
> > +		return -EINVAL;
> > +
> >  	switch (op->flags & DRM_PANTHOR_VM_BIND_OP_TYPE_MASK) {
> >  	case DRM_PANTHOR_VM_BIND_OP_TYPE_MAP:
> >  		if (!(op->flags & DRM_PANTHOR_VM_BIND_OP_MAP_SPARSE)) {
> 
> [1]https://elixir.bootlin.com/linux/v7.0.11/source/include/uapi/drm/panthor_drm.h#L588