linux-kernel - Re: [PATCH v4 11/23] iommufd/viommu: Add IOMMUFD_CMD_HW_QUEUE

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <aCauEGCqk5lVikwR@Asurada-Nvidia>
Date: Thu, 15 May 2025 20:16:32 -0700
From: Nicolin Chen <nicolinc@...dia.com>
To: "Tian, Kevin" <kevin.tian@...el.com>
CC: "jgg@...dia.com" <jgg@...dia.com>, "corbet@....net" <corbet@....net>,
	"will@...nel.org" <will@...nel.org>, "bagasdotme@...il.com"
	<bagasdotme@...il.com>, "robin.murphy@....com" <robin.murphy@....com>,
	"joro@...tes.org" <joro@...tes.org>, "thierry.reding@...il.com"
	<thierry.reding@...il.com>, "vdumpa@...dia.com" <vdumpa@...dia.com>,
	"jonathanh@...dia.com" <jonathanh@...dia.com>, "shuah@...nel.org"
	<shuah@...nel.org>, "jsnitsel@...hat.com" <jsnitsel@...hat.com>,
	"nathan@...nel.org" <nathan@...nel.org>, "peterz@...radead.org"
	<peterz@...radead.org>, "Liu, Yi L" <yi.l.liu@...el.com>,
	"mshavit@...gle.com" <mshavit@...gle.com>, "praan@...gle.com"
	<praan@...gle.com>, "zhangzekun11@...wei.com" <zhangzekun11@...wei.com>,
	"iommu@...ts.linux.dev" <iommu@...ts.linux.dev>, "linux-doc@...r.kernel.org"
	<linux-doc@...r.kernel.org>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "linux-arm-kernel@...ts.infradead.org"
	<linux-arm-kernel@...ts.infradead.org>, "linux-tegra@...r.kernel.org"
	<linux-tegra@...r.kernel.org>, "linux-kselftest@...r.kernel.org"
	<linux-kselftest@...r.kernel.org>, "patches@...ts.linux.dev"
	<patches@...ts.linux.dev>, "mochs@...dia.com" <mochs@...dia.com>,
	"alok.a.tiwari@...cle.com" <alok.a.tiwari@...cle.com>, "vasant.hegde@....com"
	<vasant.hegde@....com>
Subject: Re: [PATCH v4 11/23] iommufd/viommu: Add IOMMUFD_CMD_HW_QUEUE_ALLOC
 ioctl

On Fri, May 16, 2025 at 02:49:44AM +0000, Tian, Kevin wrote:
> > From: Nicolin Chen <nicolinc@...dia.com>
> > Sent: Friday, May 16, 2025 2:45 AM
> > 
> > On Thu, May 15, 2025 at 06:30:27AM +0000, Tian, Kevin wrote:
> > > > From: Nicolin Chen <nicolinc@...dia.com>
> > > > Sent: Friday, May 9, 2025 11:03 AM
> > > >
> > > > +
> > > > +/**
> > > > + * struct iommu_hw_queue_alloc - ioctl(IOMMU_HW_QUEUE_ALLOC)
> > > > + * @size: sizeof(struct iommu_hw_queue_alloc)
> > > > + * @flags: Must be 0
> > > > + * @viommu_id: Virtual IOMMU ID to associate the HW queue with
> > > > + * @type: One of enum iommu_hw_queue_type
> > > > + * @index: The logical index to the HW queue per virtual IOMMU for a
> > > > multi-queue
> > > > + *         model
> > >
> > > I'm thinking of an alternative way w/o having the user to assign index
> > > and allowing the driver to poke object dependency (next patch).
> > >
> > > Let's say the index is internally assigned by the driver. so this cmd is
> > > just for allowing a hw queue and it's the driver to decide the allocation
> > > policy, e.g. in ascending order.
> > >
> > > Introduce a new flag in viommu_ops to indicate to core that the
> > > new hw queue should hold a reference to the previous hw queue.
> > >
> > > core maintains a last_queue field in viommu. Upon success return
> > > from @hw_queue_alloc() the core increments the users refcnt of
> > > last_queue, records the dependency in iommufd_hw_queue struct,
> > > and update viommu->last_queue.
> > >
> > > Then the destroy order is naturally guaranteed.
> > 
> > I have thought about that too. It's nice that the core can easily
> > maintain the dependency for the driver.
> > 
> > But there would still need an out_index to mark each dynamically
> > allocated queue. So VMM would know where it should map the queue.
> > 
> > For example, if VMM wants to allocate a queue at its own index=1
> > without allocating index=0 first, kernel cannot fail that as VMM
> > doesn't provide the index. The only way left for kernel would be
> > to output the allocated queue with index=0 and then wish VMM can
> > validate it, which doesn't sound safe..
> > 
> 
> VMM's index is virtual which could be mapped to whatever queue
> object created at its own disposal.
> 
> the uAPI just requires VMM to remember a sequential list of  allocated
> queue objects and destroy them in reverse order of allocation, instead
> of in the reverse order of virtual indexes.

But that's not going to work for VCMDQ.

VINTF mmaps only a single page that controls multiple queues. And
all queues have to be mapped correctly between HW and VM indexes.
Otherwise, it won't work if VMM maps:

HW-level VINTF1 LVCMDQ0 <==> VM-level VINTF0 LVCMDQ1
HW-level VINTF1 LVCMDQ1 <==> VM-level VINTF0 LVCMDQ0

So, one way or another, kernel has to ensure the static mappings
of the indexes. And I think it's safer in the way that VMM tells
what index to allocate..

Thanks
Nicolin