linux-kernel - Re: [PATCH v4 22/23] iommu/tegra241-cmdqv: Add user-space use support

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: <aCa6sdNwutK75Lnm@Asurada-Nvidia>
Date: Thu, 15 May 2025 21:10:25 -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 22/23] iommu/tegra241-cmdqv: Add user-space use support

On Fri, May 16, 2025 at 04:00:58AM +0000, Tian, Kevin wrote:
> > From: Nicolin Chen <nicolinc@...dia.com>
> > Sent: Friday, May 16, 2025 1:14 AM
> > 
> > On Thu, May 15, 2025 at 08:27:17AM +0000, Tian, Kevin wrote:
> > > > From: Nicolin Chen <nicolinc@...dia.com>
> > > > Sent: Friday, May 9, 2025 11:03 AM
> > > >
> > > >  /**
> > > >   * struct iommu_hw_info_arm_smmuv3 - ARM SMMUv3 hardware
> > > > information
> > > >   *                                   (IOMMU_HW_INFO_TYPE_ARM_SMMUV3)
> > > >   *
> > > > - * @flags: Must be set to 0
> > > > - * @impl: Must be 0
> > > > + * @flags: Combination of enum iommu_hw_info_arm_smmuv3_flags
> > > > + * @impl: Implementation-defined bits when the following flags are set:
> > > > + *        - IOMMU_HW_INFO_ARM_SMMUV3_HAS_TEGRA241_CMDQV
> > > > + *          Bits[15:12] - Log2 of the total number of SID replacements
> > > > + *          Bits[11:08] - Log2 of the total number of VINTFs per vIOMMU
> > > > + *          Bits[07:04] - Log2 of the total number of VCMDQs per vIOMMU
> > > > + *          Bits[03:00] - Version number for the CMDQ-V HW
> > >
> > > hmm throughout this series I drew an equation between VINTF
> > > and vIOMMU. Not sure how multiple VINTFs can be represented
> > > w/o introducing more objects. Do we want to keep such info here?
> > 
> > You are right that VINTF=vIOMMU. This is a per SMMU instance ioctl.
> > So, each VM should only have one VTINF/vIOMMU per SMMU instance.
> > 
> > For multi-VINTF (multi-vIOMMU) case, there needs to be more SMMUs
> > backing passthrough devices being assigned to the VM.
> > 
> > What exactly the concern of keeping this info here?
> 
> First, you agreed that VINTF=vIOMMU, then "total number of VINTFs
> per vIOMMU" doesn't make sense as it's fixed to 1 in concept.
> 
> Then, each VM can only get one VINTF/vIOMMU per SMMU instance,
> and this ioctl is per SMMU instance. This also implies that only one
> VINTF can be reported in the ioctl.
> 
> In multi-VINTF case, the VM should get 1VINTF per ioctl from each
> SMMU backing passthrough devices.
> 
> Then what is the point of " Bits[11:08] - Log2 of the total number
> of VINTFs per vIOMMU "?

It was not there in the previous version. Pranjal pointed out that
it was missing a field.

You are right that this field must set to 0, indicating only single
VINTF is allowed.

Given Jason's comments about this impl rework (to a data structure),
I think I will just drop this number of VTINFs. Instead will add a
line of comments say that VMM should set this field to 0, i.e. only
provide VM one VINTF per SMMU.

Thanks
Nicolin