linux-kernel - Re: [PATCH v5 17/29] iommufd: Add mmap interface

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Message-ID: <20250530171223.GN233377@nvidia.com>
Date: Fri, 30 May 2025 14:12:23 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: Nicolin Chen <nicolinc@...dia.com>
Cc: kevin.tian@...el.com, corbet@....net, will@...nel.org,
	bagasdotme@...il.com, robin.murphy@....com, joro@...tes.org,
	thierry.reding@...il.com, vdumpa@...dia.com, jonathanh@...dia.com,
	shuah@...nel.org, jsnitsel@...hat.com, nathan@...nel.org,
	peterz@...radead.org, yi.l.liu@...el.com, mshavit@...gle.com,
	praan@...gle.com, zhangzekun11@...wei.com, iommu@...ts.linux.dev,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-tegra@...r.kernel.org,
	linux-kselftest@...r.kernel.org, patches@...ts.linux.dev,
	mochs@...dia.com, alok.a.tiwari@...cle.com, vasant.hegde@....com,
	dwmw2@...radead.org, baolu.lu@...ux.intel.com
Subject: Re: [PATCH v5 17/29] iommufd: Add mmap interface

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