linux-kernel - Re: [PATCH v2 10/19] iommufd/viommu: Add vdev

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Message-ID: <ZwQOAvoJrMWOuxxd@Asurada-Nvidia>
Date: Mon, 7 Oct 2024 09:36:18 -0700
From: Nicolin Chen <nicolinc@...dia.com>
To: Jason Gunthorpe <jgg@...dia.com>
CC: <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>
Subject: Re: [PATCH v2 10/19] iommufd/viommu: Add vdev_id helpers for IOMMU
 drivers

On Mon, Oct 07, 2024 at 12:38:37PM -0300, Jason Gunthorpe wrote:
> On Fri, Oct 04, 2024 at 10:19:43PM -0700, Nicolin Chen wrote:
> > I tried exposing the struct iommufd_viommu to drivers, and was
> > able to drop a couple of helpers, except these two:
> > 
> > struct device *vdev_to_dev(struct iommufd_vdevice *vdev)
> > {
> > 	return vdev ? vdev->idev->dev : NULL;
> > } // Without it, we need to expose struct iommufd_device.
> > 
> > struct iommu_domain *
> > iommufd_viommu_to_parent_domain(struct iommufd_viommu *viommu)
> > {
> > 	if (!viommu || !viommu->hwpt)
> > 		return NULL;
> > 	return viommu->hwpt->common.domain;
> > } // Without it, we need to expose struct iommufd_hwpt_page.
> 
> It seems OK, there isn't really locking entanglements or performance
> path on this stuff?

-----
The typical use case of the first one is like:
	dev = vdev_to_dev(xa_load(&viommu->vdevs, (unsigned long)vdev_id));
so I am asking for:
/* Caller should lock via viommu->vdevs_rwsem with proper permission */

-----
And for the second one:
/*
 * Convert a viommu to the encapsulated nesting parent domain. A caller must be
 * aware of the life cycle of the viommu pointer: only call this function in a
 * callback functions of viommu_alloc or a viommu op.
 */
-----

Thanks
Nicolin