linux-kernel - Re: [PATCH v2 00/17] Add Nested Translation Support for SMMUv3

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Date:   Wed, 10 May 2023 01:41:14 -0700
From:   Nicolin Chen <nicolinc@...dia.com>
To:     "Tian, Kevin" <kevin.tian@...el.com>,
        "jgg@...dia.com" <jgg@...dia.com>,
        "robin.murphy@....com" <robin.murphy@....com>,
        "will@...nel.org" <will@...nel.org>
CC:     "eric.auger@...hat.com" <eric.auger@...hat.com>,
        "baolu.lu@...ux.intel.com" <baolu.lu@...ux.intel.com>,
        "joro@...tes.org" <joro@...tes.org>,
        "shameerali.kolothum.thodi@...wei.com" 
        <shameerali.kolothum.thodi@...wei.com>,
        "jean-philippe@...aro.org" <jean-philippe@...aro.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "alex.williamson@...hat.com" <alex.williamson@...hat.com>,
        "Liu, Yi L" <yi.l.liu@...el.com>
Subject: Re: [PATCH v2 00/17] Add Nested Translation Support for SMMUv3

On Wed, May 10, 2023 at 08:11:28AM +0000, Tian, Kevin wrote:
 
> > From: Nicolin Chen <nicolinc@...dia.com>
> > Sent: Wednesday, May 10, 2023 11:33 AM
> >
> > One unique requirement for SMMUv3 nested translation support is the MSI
> > doorbell address translation, which is a 2-stage translation too. And,
> > to working with the ITS driver, an msi_cookie needs to be setup on the
> > kernel-managed domain, the stage-2 domain of the nesting setup. And the
> > same msi_cookie will be fetched, via
> > iommu_dma_get_msi_mapping_domain(),
> > in the iommu core to allocate and creates IOVA mappings for MSI doorbell
> > page(s). However, with the nesting design, the device is attached to a
> > user-managed domain, the stage-1 domain. So both the setup and fetching
> > of the msi_cookie would not work at the level of stage-2 domain. Thus,
> > on both sides, the msi_cookie setup and fetching require a redirection
> > of the domain pointer. It's easy to do so in iommufd core, but needs a
> > new op in the iommu core and driver.
> >
> 
> Looks the new preferred way is to map the physical ITS page to an IPA
> provided by Qemu then let the guest allocate the cookie in S1 which
> is then passed back by Qemu to the host kernel? [1]
> 
> [1] https://lore.kernel.org/linux-iommu/5ff0d72b-a7b8-c8a9-60e5-396e7a1ef363@arm.com/

Hmm..is that something firm to implement at this stage?

Thank you
Nicolin