Messages in this thread | | | From | Shameerali Kolothum Thodi <> | Subject | RE: [PATCH v1 02/14] iommufd: Add nesting related data structures for ARM SMMUv3 | Date | Thu, 9 Mar 2023 16:07:54 +0000 |
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> -----Original Message----- > From: Jason Gunthorpe [mailto:jgg@nvidia.com] > Sent: 09 March 2023 16:00 > To: Shameerali Kolothum Thodi <shameerali.kolothum.thodi@huawei.com> > Cc: Jean-Philippe Brucker <jean-philippe@linaro.org>; Nicolin Chen > <nicolinc@nvidia.com>; robin.murphy@arm.com; will@kernel.org; > eric.auger@redhat.com; kevin.tian@intel.com; baolu.lu@linux.intel.com; > joro@8bytes.org; linux-arm-kernel@lists.infradead.org; > iommu@lists.linux.dev; linux-kernel@vger.kernel.org; yi.l.liu@intel.com > Subject: Re: [PATCH v1 02/14] iommufd: Add nesting related data structures > for ARM SMMUv3 > > On Thu, Mar 09, 2023 at 03:51:42PM +0000, Shameerali Kolothum Thodi > wrote: > > > > For ARM cases where there is no shared VMID space with KVM, the ARM > > > VMID should be somehow assigned to the iommfd_ctx itself and the alloc > > > domain op should receive it from there. > > > > Is there any use of VMID outside SMMUv3? I was thinking if nested domain > alloc > > doesn't provide the KVM instance, then SMMUv3 can use its internal VMID. > > When we talk about exposing an SMMUv3 IOMMU CMDQ directly to > userspace then > VMID is the security token that protects it. > > So in that environment every domain under the same iommufd should > share the same VMID so that the CMDQ's also share the same VMID. > > I expect this to be a common sort of requirement as we will see > userspace command queues in the other HW as well. > > So, I suppose the answer for now is that ARM SMMUv3 should just > allocate one VMID per iommu_domain and there should be no VMID in the > uapi at all. > > Moving all iommu_domains to share the same VMID is a future patch. > > Though.. I have no idea how vVMID is handled in the SMMUv3 > architecture. I suppose the guest IOMMU HW caps are set in a way that > it knows it does not have VMID?
I think, Guest only sets up the SMMUv3 S1 stage and it doesn't use VMID.
Thanks, Shameer
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