linux-kernel - Re: [PATCH v5 14/29] iommufd/viommu: Add IOMMUFD_CMD_HW_QUEUE

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Message-ID: <20250530174037.GR233377@nvidia.com>
Date: Fri, 30 May 2025 14:40:37 -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,
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	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 14/29] iommufd/viommu: Add IOMMUFD_CMD_HW_QUEUE_ALLOC
 ioctl

On Fri, May 30, 2025 at 10:38:24AM -0700, Nicolin Chen wrote:
> On Fri, May 30, 2025 at 01:14:55PM -0300, Jason Gunthorpe wrote:
> > On Sat, May 17, 2025 at 08:21:31PM -0700, Nicolin Chen wrote:
> > > +	offset =
> > > +		cmd->nesting_parent_iova - PAGE_ALIGN(cmd->nesting_parent_iova);
> > > +	max_npages = DIV_ROUND_UP(offset + cmd->length, PAGE_SIZE);
> > 
> > This should probably be capped to PAGE_SIZE/sizeof(void *), return
> > EINVAL if not
> 
> Hmm, mind elaborating where this PAGE_SIZE/sizeof comes from?

We can usually allocate up to a PAGE_SIZE without too much
trouble. Beyond that it gets more likely to fail.

> > > +	hw_queue->viommu = viommu;
> > > +	refcount_inc(&viommu->obj.users);
> > > +	hw_queue->length = cmd->length;
> > > +	hw_queue->base_addr = cmd->nesting_parent_iova;
> > 
> > When the driver is running, which can be a source of bugs.
> 
> Hmm, I don't quite follow the "bugs" here. Any example?

Like if the driver thinks that hw_queue->length should be valid during
init, it turns out it isn't.

Jason