linux-kernel - RE: [PATCH v2 08/10] iommufd/device: Use iommu_group_replace

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Message-ID: <BN9PR11MB5276768FA501B5CD573745108CA39@BN9PR11MB5276.namprd11.prod.outlook.com>
Date:   Wed, 15 Feb 2023 07:24:30 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     Nicolin Chen <nicolinc@...dia.com>
CC:     Jason Gunthorpe <jgg@...dia.com>,
        "joro@...tes.org" <joro@...tes.org>,
        "will@...nel.org" <will@...nel.org>,
        "robin.murphy@....com" <robin.murphy@....com>,
        "alex.williamson@...hat.com" <alex.williamson@...hat.com>,
        "shuah@...nel.org" <shuah@...nel.org>,
        "Liu, Yi L" <yi.l.liu@...el.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kselftest@...r.kernel.org" <linux-kselftest@...r.kernel.org>,
        "baolu.lu@...ux.intel.com" <baolu.lu@...ux.intel.com>
Subject: RE: [PATCH v2 08/10] iommufd/device: Use iommu_group_replace_domain()

> From: Nicolin Chen <nicolinc@...dia.com>
> Sent: Wednesday, February 15, 2023 3:15 PM
> 
> But things will be out of control, if user space continues mapping
> something onto domain1's iopt for idev2, even after it is attached
> covertly to domain2's iopt by the replace routine. I wonder how
> kernel should handle this and keep the consistency between IOMMUFD
> objects and iommu_group.
> 

this is where I don't understand.

domain mapping just reflects what an address space has.

Take Qemu for example. w/o vIOMMU domain mappings is added/
removed according to the change in the GPA address space.

w/ vIOMMU then it is synced with guest page table.

why would userspace construct mappings for a specific device?

when device is moved from one domain to another domain, it just
bears with whatever the new domain allows it to access.