linux-kernel - RE: [PATCH v1 01/14] iommu: Add iommu_get_unmanaged

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Date:   Fri, 10 Mar 2023 15:44:02 +0000
From:   Shameerali Kolothum Thodi <shameerali.kolothum.thodi@...wei.com>
To:     Jason Gunthorpe <jgg@...dia.com>,
        Eric Auger <eric.auger@...hat.com>
CC:     Nicolin Chen <nicolinc@...dia.com>,
        "robin.murphy@....com" <robin.murphy@....com>,
        "will@...nel.org" <will@...nel.org>,
        "kevin.tian@...el.com" <kevin.tian@...el.com>,
        "baolu.lu@...ux.intel.com" <baolu.lu@...ux.intel.com>,
        "joro@...tes.org" <joro@...tes.org>,
        "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>
Subject: RE: [PATCH v1 01/14] iommu: Add iommu_get_unmanaged_domain helper



> -----Original Message-----
> From: Jason Gunthorpe [mailto:jgg@...dia.com]
> Sent: 10 March 2023 15:33
> To: Eric Auger <eric.auger@...hat.com>
> Cc: Nicolin Chen <nicolinc@...dia.com>; robin.murphy@....com;
> will@...nel.org; kevin.tian@...el.com; baolu.lu@...ux.intel.com;
> joro@...tes.org; Shameerali Kolothum Thodi
> <shameerali.kolothum.thodi@...wei.com>; jean-philippe@...aro.org;
> linux-arm-kernel@...ts.infradead.org; iommu@...ts.linux.dev;
> linux-kernel@...r.kernel.org
> Subject: Re: [PATCH v1 01/14] iommu: Add iommu_get_unmanaged_domain
> helper
> 
> On Fri, Mar 10, 2023 at 11:14:59AM +0100, Eric Auger wrote:
> > Hi Nicolin,
> >
> > On 3/9/23 11:53, Nicolin Chen wrote:
> > > The nature of ITS virtualization on ARM is done via hypercalls, so
> > > kernel handles all IOVA mappings for the MSI doorbell in
> > > iommu_dma_prepare_msi() and iommu_dma_compose_msi_msg(). The
> current
> > > virtualization solution with a 2-stage nested translation setup is
> > > to do 1:1 IOVA mappings at stage-1
> > Note that if we still intend to use that trick there is a known issue
> > at kernel side that needs to be fixed.
> >
> > ARM DEN 0049E.b IORT specification mandates that when RMRs are
> > present, the OS must preserve PCIe configuration performed by the boot
> > FW.
> 
> This limitation doesn't seem necessary for this MSI stuff?
> 
> What is it for?

That is to make sure the Stream Ids specified in RMR are still valid and is not being
reassigned by OS. The kernel checks for this(iort_rmr_has_dev()),
https://lore.kernel.org/linux-arm-kernel/20220420164836.1181-5-shameerali.kolothum.thodi@huawei.com/

Thanks,
Shameer