linux-kernel - Re: [PATCH v2 13/22] iommufd: Add mmap interface

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Message-ID: <20250507123901.GF90261@nvidia.com>
Date: Wed, 7 May 2025 09:39:01 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: Nicolin Chen <nicolinc@...dia.com>
Cc: Pranjal Shrivastava <praan@...gle.com>, 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, 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
Subject: Re: [PATCH v2 13/22] iommufd: Add mmap interface

On Tue, May 06, 2025 at 12:30:54PM -0700, Nicolin Chen wrote:

> So, if I understand it correctly, what we want to achieve is to
> have maple tree to manage all PFN ranges. And each range holds
> the same entry, a structure that we can use to verify the sanity
> of an mmap? Let's say for PFNs A->B, the tree should store the
> structure between index A and index B (inclusive)?

And tell you what has been mmap'd.

> If this is correct, mtree_alloc_range() that is given a range of
> [0, ULONG_MAX] would allocate the PFN range from the lowest index
> (i.e. 0) instead of PFN A?

mtree_alloc_range() returns a new range of PFNs that does not overlap
with any existing range. It should always be called on O->U32_MAX (for
32bit uapi compat) and it should always pick the range to use.

Jason