[PATCH v5 17/29] iommufd: Add mmap interface

[Jason Gunthorpe]

On Fri, May 30, 2025 at 09:59:36AM -0700, Nicolin Chen wrote:
> > > +/* The vm_pgoff must be pre-allocated from mt_mmap, and given to user space */
> > > +static int iommufd_fops_mmap(struct file *filp, struct vm_area_struct *vma)
> > > +{
> > > +	struct iommufd_ctx *ictx = filp->private_data;
> > > +	size_t length = vma->vm_end - vma->vm_start;
> > > +	struct iommufd_mmap *immap;
> > > +	int rc;
> > > +
> > > +	if (!PAGE_ALIGNED(length))
> > > +		return -EINVAL;
> > > +	if (!(vma->vm_flags & VM_SHARED))
> > > +		return -EINVAL;
> > > +	if (vma->vm_flags & VM_EXEC)
> > > +		return -EPERM;
> > > +
> > > +	/* vma->vm_pgoff carries an index to an mtree entry (immap) */
> > > +	immap = mtree_load(&ictx->mt_mmap, vma->vm_pgoff);
> > > +	if (!immap)
> > > +		return -ENXIO;
> > > +	/* Validate the vm_pgoff and length against the registered region */
> > > +	if (vma->vm_pgoff != immap->startp)
> > > +		return -ENXIO;
> > 
> > This check seems redundant
> 
> Hmm, I was trying to follow your remarks:
> "This needs to validate that vm_pgoff is at the start of the immap"
> https://lore.kernel.org/all/20250515164717.GL382960@nvidia.com/

Oh, right I forgot how mtree_load works again. :\ Maybe add a little
note

/* mtree_load returns the immap for any contained pgoff, only allow
   the immap thing to be mapped. */

Jason