linux-kernel - Re: [PATCH 02/17] iommu: Add nested domain support

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Date:   Tue, 14 Feb 2023 10:47:27 -0800
From:   Nicolin Chen <nicolinc@...dia.com>
To:     Yi Liu <yi.l.liu@...el.com>
CC:     <joro@...tes.org>, <alex.williamson@...hat.com>, <jgg@...dia.com>,
        <kevin.tian@...el.com>, <robin.murphy@....com>,
        <cohuck@...hat.com>, <eric.auger@...hat.com>,
        <kvm@...r.kernel.org>, <mjrosato@...ux.ibm.com>,
        <chao.p.peng@...ux.intel.com>, <yi.y.sun@...ux.intel.com>,
        <peterx@...hat.com>, <jasowang@...hat.com>,
        <shameerali.kolothum.thodi@...wei.com>, <lulu@...hat.com>,
        <suravee.suthikulpanit@....com>, <iommu@...ts.linux.dev>,
        <linux-kernel@...r.kernel.org>, <linux-kselftest@...r.kernel.org>,
        <baolu.lu@...ux.intel.com>
Subject: Re: [PATCH 02/17] iommu: Add nested domain support

On Wed, Feb 08, 2023 at 08:31:38PM -0800, Yi Liu wrote:
> From: Lu Baolu <baolu.lu@...ux.intel.com>
> 
> Introduce a new domain type for a user space I/O address, which is nested
> on top of another user space address represented by a UNMANAGED domain. The
> mappings of a nested domain are managed by user space software, therefore
> it's unnecessary to have map/unmap callbacks. But the updates of the PTEs
> in the nested domain page table must be propagated to the caches on both
> IOMMU (IOTLB) and devices (DevTLB).
> 
> The nested domain is allocated by the domain_alloc_user op, and attached
> to the device through the existing iommu_attach_device/group() interfaces.
> 
> An new domain op, named iotlb_sync_user is added for the userspace to flush
> the hardware caches for a nested domain through iommufd. No wrapper for it
> as it's only supposed to be used by iommufd.

Following the remarks from Jason and Robin in their first looks
at the nested SMMU changes, perhaps we should rename this op
"iotlb_sync_user" back to "cache_invalidate_user" or so, since
the type for the caches on VT-d isn't confined to IOTLB either.

Thanks
Nic