Messages in this thread | | | Date | Tue, 21 Mar 2023 22:14:44 -0700 | From | Nicolin Chen <> | Subject | Re: [PATCH v1 14/14] iommu/arm-smmu-v3: Add arm_smmu_cache_invalidate_user |
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On Mon, Mar 20, 2023 at 07:14:17PM -0300, Jason Gunthorpe wrote: > On Mon, Mar 20, 2023 at 01:46:52PM -0700, Nicolin Chen wrote: > > On Mon, Mar 20, 2023 at 03:07:13PM -0300, Jason Gunthorpe wrote: > > > On Mon, Mar 20, 2023 at 09:35:20AM -0700, Nicolin Chen wrote: > > > > > > > > You need to know what devices the vSID is targetting ang issues > > > > > invalidations only for those devices. > > > > > > > > I agree with that, yet cannot think of a solution to achieve > > > > that out of vSID. QEMU code by means of emulating a physical > > > > SMMU only reads the commands from the queue, without knowing > > > > which device (vSID) actually sent these commands. > > > > > > Huh? > > > > > > CMD_ATC_INV has the SID > > > > > > Other commands have the ASID. > > > > > > You never need to cross an ASID to a SID or vice versa. > > > > > > If the guest is aware of ATS it will issue CMD_ATC_INV with vSIDs, and > > > the hypervisor just needs to convert vSID to pSID. > > > > > > Otherwise vSID doesn't matter because it isn't used in the invalidation > > > API and you are just handling ASIDs that only need the VM_ID scope > > > applied. > > > > Yea, I was thinking of your point (at the top) how we could > > ensure if an invalidation is targeting a correct vSID. So, > > that narrative was only about CMD_ATC_INV... > > > > Actually, we don't forward CMD_ATC_INV in QEMU. In another > > thread, Kevin also remarked whether we need to support that > > in the host or not. And I plan to drop CMD_ATC_INV from the > > list of cache_invalidate_user(), following his comments and > > the QEMU situation. Our uAPI, either forwarding the commands > > or a package of queue info, should be able to cover this in > > the future whenever we think it's required. > > Something has to generate CMD_ATC_INV. > > How do you plan to generate this from the hypervisor based on ASID > invalidations? > > The hypervisor doesn't know what ASIDs are connected to what SIDs to > generate the ATC? > > Intel is different, they know what devices the vDID is connected to, > so when they get a vDID invalidation they can elaborate it into a ATC > invalidation. ARM doesn't have that information.
I see. Perhaps vSMMU still needs to forward CMD_ATC_INV. And, as you suggested, it should go through a vSID sanity check by the host handler. We can find the corresponding pSID to check if the device is associated with the iommu_domain?
Thanks Nic
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