Messages in this thread | | | Date | Thu, 9 Mar 2023 21:04:20 -0800 | From | Nicolin Chen <> | Subject | Re: [PATCH v1 02/14] iommufd: Add nesting related data structures for ARM SMMUv3 |
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Hi Jeans,
Allow me to partially reply your email:
On Thu, Mar 09, 2023 at 01:42:17PM +0000, Jean-Philippe Brucker wrote:
> > +struct iommu_hwpt_arm_smmuv3 { > > +#define IOMMU_SMMUV3_FLAG_S2 (1 << 0) /* if unset, stage-1 */ > > I don't understand the purpose of this flag, since the structure only > provides stage-1 configuration fields
I should have probably put more description for this flag. It is used to allocate a stage-2 domain for a nested translation setup. The default allocation for a kernel-managed domain will allocate an S1 format of IO page table, at ARM_SMMU_DOMAIN_S1 stage. But a nested kernel-managed domain needs an S2 format, at ARM_SMMU_DOMAIN_S2. So the whole structure seems to only provide stage-1 info but it's used for both stages. And a stage-2 allocation will only need s2vmid if VMID flag is set (explaining below).
> > +#define IOMMU_SMMUV3_FLAG_VMID (1 << 1) /* vmid override */ > > Doesn't this break isolation? The VMID space is global for the SMMU, so > the guest could access cached mappings of another device
This flag isn't mature yet. I kept it from my internal RFC to see if we can have a better solution. There are use cases on certain platforms where the VMIDs across all devices in the same VM need to be aligned.
Thanks Nic
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