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Date:   Wed, 21 Jun 2023 09:07:25 -0300
From:   Jason Gunthorpe <jgg@nvidia.com>
To:     "Duan, Zhenzhong" <zhenzhong.duan@intel.com>
Cc:     "Tian, Kevin" <kevin.tian@intel.com>,
        "Liu, Yi L" <yi.l.liu@intel.com>,
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Subject: Re: [PATCH v2 00/11] iommufd: Add nesting infrastructure
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On Wed, Jun 21, 2023 at 08:29:09AM +0000, Duan, Zhenzhong wrote:
> >-----Original Message-----
> >From: Jason Gunthorpe <jgg@nvidia.com>
> >Sent: Tuesday, June 20, 2023 8:47 PM
> >Subject: Re: [PATCH v2 00/11] iommufd: Add nesting infrastructure
> >
> >On Tue, Jun 20, 2023 at 01:43:42AM +0000, Tian, Kevin wrote:
> >> I wonder whether we have argued passed each other.
> >>
> >> This series adds reserved regions to S2. I challenged the necessity as
> >> S2 is not directly accessed by the device.
> >>
> >> Then you replied that doing so still made sense to support identity
> >> S1.
> >
> >I think I said/ment if we attach the "s2" iommu domain as a direct attach for
> >identity - eg at boot time, then the IOAS must gain the reserved regions. This is
> >our normal protocol.
> There is code to fail the attaching for device with RMRR in intel iommu driver,
> do we plan to remove below check for IOMMUFD soon or later?
> 
> static int intel_iommu_attach_device(struct iommu_domain *domain,
>                                      struct device *dev)
> {
>         struct device_domain_info *info = dev_iommu_priv_get(dev);
>         int ret;
> 
>         if (domain->type == IOMMU_DOMAIN_UNMANAGED &&
>             device_is_rmrr_locked(dev)) {
>                 dev_warn(dev, "Device is ineligible for IOMMU domain attach due to platform RMRR requirement.  Contact your platform vendor.\n");
>                 return -EPERM;
>         }

Not really, systems with RMRR cannot support VFIO at all. Baolu sent a
series lifting this restriction up higher in the stack:

https://lore.kernel.org/all/20230607035145.343698-1-baolu.lu@linux.intel.com/

Jason