linux-kernel - Re: [PATCH v5 06/13] iommufd: Allow pt_id to carry viommu_id for IOMMU_HWPT

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Message-ID: <20241029152746.GE209124@nvidia.com>
Date: Tue, 29 Oct 2024 12:27:46 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: Nicolin Chen <nicolinc@...dia.com>
Cc: Zhangfei Gao <zhangfei.gao@...aro.org>, kevin.tian@...el.com,
	will@...nel.org, joro@...tes.org, suravee.suthikulpanit@....com,
	robin.murphy@....com, dwmw2@...radead.org, baolu.lu@...ux.intel.com,
	shuah@...nel.org, linux-kernel@...r.kernel.org,
	iommu@...ts.linux.dev, linux-arm-kernel@...ts.infradead.org,
	linux-kselftest@...r.kernel.org, eric.auger@...hat.com,
	jean-philippe@...aro.org, mdf@...nel.org, mshavit@...gle.com,
	shameerali.kolothum.thodi@...wei.com, smostafa@...gle.com,
	yi.l.liu@...el.com, aik@....com, patches@...ts.linux.dev
Subject: Re: [PATCH v5 06/13] iommufd: Allow pt_id to carry viommu_id for
 IOMMU_HWPT_ALLOC

On Mon, Oct 28, 2024 at 07:52:10AM -0700, Nicolin Chen wrote:
> On Mon, Oct 28, 2024 at 10:03:09AM -0300, Jason Gunthorpe wrote:
> > On Mon, Oct 28, 2024 at 11:24:10AM +0800, Zhangfei Gao wrote:
> > 
> > > > +/**
> > > > + * iommufd_viommu_alloc_hwpt_nested() - Get a hwpt_nested for a vIOMMU
> > > > + * @viommu: vIOMMU ojbect to associate the hwpt_nested/domain with
> > > > + * @user_data: user_data pointer. Must be valid
> > > > + *
> > > > + * Allocate a new IOMMU_DOMAIN_NESTED for a vIOMMU and return it as a NESTED
> > > > + * hw_pagetable.
> > > > + */
> > > > +static struct iommufd_hwpt_nested *
> > > > +iommufd_viommu_alloc_hwpt_nested(struct iommufd_viommu *viommu, u32 flags,
> > > > +                                const struct iommu_user_data *user_data)
> > > > +{
> > > > +       struct iommufd_hwpt_nested *hwpt_nested;
> > > > +       struct iommufd_hw_pagetable *hwpt;
> > > > +       int rc;
> > > > +
> > > > +       if (flags)
> > > > +               return ERR_PTR(-EOPNOTSUPP);
> > > 
> > > This check should be removed.
> > > 
> > > When a user page fault is required, IOMMU_HWPT_FAULT_ID_VALID is set.
> > > if (cmd->flags & IOMMU_HWPT_FAULT_ID_VALID) {
> > 
> > It can't just be removed..
> > 
> > I suspect that IOMMU_HWPT_FAULT_ID_VALID should not be set on the
> > nested domain but on the parent?
> 
> By giving another look,
> 
> In iommufd_hwpt_paging_alloc(), we reject IOMMU_HWPT_FAULT_ID_VALID:
> 	const u32 valid_flags = IOMMU_HWPT_ALLOC_NEST_PARENT |
> 				IOMMU_HWPT_ALLOC_DIRTY_TRACKING;
> 	...
> 	if (flags & ~valid_flags)
> 		return ERR_PTR(-EOPNOTSUPP);
> 
> In iommufd_hwpt_nested_alloc(), we mask the flag away:
> 	if ((flags & ~IOMMU_HWPT_FAULT_ID_VALID) ||
> 	    !user_data->len || !ops->domain_alloc_user)
> 		return ERR_PTR(-EOPNOTSUPP);
> 	...
> 	hwpt->domain = ops->domain_alloc_user(idev->dev,
> 					      flags & ~IOMMU_HWPT_FAULT_ID_VALID,
> 					      parent->common.domain, user_data);
> 
> Then, in the common function it has a section of
> 	if (cmd->flags & IOMMU_HWPT_FAULT_ID_VALID) {
> 	...
> 
> It seems that this IOMMU_HWPT_FAULT_ID_VALID is for nested domains?

OK, but ARM should be blocking it since it doesn't work there.

I think we made some error here, it should have been passed in flags
to the drivers and only intel should have accepted it.

This suggests we should send flags down the viommu alloc domain path too.

Jason