From: Jason Gunthorpe <jgg@nvidia.com>
To: Nicolin Chen <nicolinc@nvidia.com>
Cc: "Tian, Kevin" <kevin.tian@intel.com>,
"will@kernel.org" <will@kernel.org>,
"robin.murphy@arm.com" <robin.murphy@arm.com>,
"suravee.suthikulpanit@amd.com" <suravee.suthikulpanit@amd.com>,
"joro@8bytes.org" <joro@8bytes.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"iommu@lists.linux.dev" <iommu@lists.linux.dev>,
"linux-arm-kernel@lists.infradead.org"
<linux-arm-kernel@lists.infradead.org>,
"linux-tegra@vger.kernel.org" <linux-tegra@vger.kernel.org>,
"Liu, Yi L" <yi.l.liu@intel.com>,
"eric.auger@redhat.com" <eric.auger@redhat.com>,
"vasant.hegde@amd.com" <vasant.hegde@amd.com>,
"jon.grimm@amd.com" <jon.grimm@amd.com>,
"santosh.shukla@amd.com" <santosh.shukla@amd.com>,
"Dhaval.Giani@amd.com" <Dhaval.Giani@amd.com>,
"shameerali.kolothum.thodi@huawei.com"
<shameerali.kolothum.thodi@huawei.com>
Subject: Re: [PATCH RFCv1 08/14] iommufd: Add IOMMU_VIOMMU_SET_DEV_ID ioctl
Date: Tue, 11 Jun 2024 09:17:56 -0300 [thread overview]
Message-ID: <20240611121756.GT19897@nvidia.com> (raw)
In-Reply-To: <Zmed4AtFjuF7+lWd@Asurada-Nvidia>
On Mon, Jun 10, 2024 at 05:44:16PM -0700, Nicolin Chen wrote:
> On Mon, Jun 10, 2024 at 09:28:39PM -0300, Jason Gunthorpe wrote:
> > On Mon, Jun 10, 2024 at 04:04:30PM -0700, Nicolin Chen wrote:
> >
> > > > > Actually, even now as we put a dispatcher in VMM, VMM still does
> > > > > decode the CD table to link ASID to s1_hwpt. Otherwise, it could
> > > > > only broadcast a TLBI cmd to all pSMMUs.
> > > >
> > > > No, there should be no CD table decoding and no linking ASID to
> > > > anything by the VMM.
> > > >
> > > > The ARM architecture is clean, the ASID can remain private to the VM,
> > > > there is no reason for the VMM to understand it.
> > >
> > > But a guest-level TLBI command usually has only ASID available to
> > > know which pSMMU to dispatch the command. Without an ASID lookup
> > > table, how could VMM then dispatch a command to the corresponding
> > > pSMMU?
> >
> > It can broadcast. The ARM architecture does not expect a N:1 mapping
> > of SMMUs. This is why I think it is not such a good idea..
>
> Hmm, I thought we had an agreed idea that we shouldn't broadcast
> a TLBI (except global NH_ALL/VAA) for invalidation performance?
I wouldn't say agree, there are just lots of different trade offs to
be made here. You can reduce broadcast by parsing the CD table from
the VMM. You can reduce broadcast with multiple vSMMUs.
VMM needs to pick a design. I favour multiple vSMMUs.
> CD table walkthrough would be always done only by VMM, while the
> lookup table could be created/maintained by the kernel. I feel a
> vasid table could make sense since we maintain the vdev_id table
> in the kernel space too.
I'm not convinced we should put such a micro optimization in the
kernel. If the VMM cares about performance then split the vSMMU,
otherwise lets just put all the mess in the VMM and give it the tools
to manage the invalidation distribution.
In the long run things like vCMDQ are going to force the choice to
multi-smmu, which is why I don't see too much value with investing in
optimizing the single vSMMU case. The optimization can be done later
if someone does have a use case.
Jason
next prev parent reply other threads:[~2024-06-11 12:18 UTC|newest]
Thread overview: 118+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-13 3:46 [PATCH RFCv1 00/14] Add Tegra241 (Grace) CMDQV Support (part 2/2) Nicolin Chen
2024-04-13 3:46 ` [PATCH RFCv1 01/14] iommufd: Move iommufd_object to public iommufd header Nicolin Chen
2024-05-12 13:21 ` Jason Gunthorpe
2024-05-12 22:40 ` Nicolin Chen
2024-05-13 22:30 ` Jason Gunthorpe
2024-04-13 3:46 ` [PATCH RFCv1 02/14] iommufd: Swap _iommufd_object_alloc and __iommufd_object_alloc Nicolin Chen
2024-05-12 13:26 ` Jason Gunthorpe
2024-05-13 2:29 ` Nicolin Chen
2024-05-13 3:44 ` Nicolin Chen
2024-05-13 22:30 ` Jason Gunthorpe
2024-04-13 3:47 ` [PATCH RFCv1 03/14] iommufd: Prepare for viommu structures and functions Nicolin Chen
2024-05-12 13:42 ` Jason Gunthorpe
2024-05-13 2:35 ` Nicolin Chen
2024-04-13 3:47 ` [PATCH RFCv1 04/14] iommufd: Add struct iommufd_viommu and iommufd_viommu_ops Nicolin Chen
2024-05-12 14:03 ` Jason Gunthorpe
2024-05-13 3:34 ` Nicolin Chen
2024-05-14 15:55 ` Jason Gunthorpe
2024-05-22 8:58 ` Tian, Kevin
2024-05-22 9:57 ` Baolu Lu
2024-05-22 13:39 ` Jason Gunthorpe
2024-05-23 1:43 ` Tian, Kevin
2024-05-23 4:01 ` Nicolin Chen
2024-05-23 5:40 ` Tian, Kevin
2024-05-23 12:58 ` Jason Gunthorpe
2024-05-24 2:16 ` Tian, Kevin
2024-05-24 13:03 ` Jason Gunthorpe
2024-05-24 2:36 ` Tian, Kevin
2024-04-13 3:47 ` [PATCH RFCv1 05/14] iommufd: Add IOMMUFD_OBJ_VIOMMU and IOMMUFD_CMD_VIOMMU_ALLOC Nicolin Chen
2024-05-12 14:27 ` Jason Gunthorpe
2024-05-13 4:33 ` Nicolin Chen
2024-05-14 15:38 ` Jason Gunthorpe
2024-05-15 1:20 ` Nicolin Chen
2024-05-21 18:05 ` Jason Gunthorpe
2024-05-22 0:13 ` Nicolin Chen
2024-05-22 16:46 ` Jason Gunthorpe
2024-04-13 3:47 ` [PATCH RFCv1 06/14] iommufd/selftest: Add IOMMU_VIOMMU_ALLOC test coverage Nicolin Chen
2024-04-13 3:47 ` [PATCH RFCv1 07/14] iommufd: Add viommu set/unset_dev_id ops Nicolin Chen
2024-05-12 14:46 ` Jason Gunthorpe
2024-05-13 4:39 ` Nicolin Chen
2024-05-14 15:53 ` Jason Gunthorpe
2024-05-15 1:59 ` Nicolin Chen
2024-05-21 18:24 ` Jason Gunthorpe
2024-05-21 22:27 ` Nicolin Chen
2024-05-22 13:59 ` Jason Gunthorpe
2024-05-23 6:19 ` Tian, Kevin
2024-05-23 15:01 ` Jason Gunthorpe
2024-05-24 2:21 ` Tian, Kevin
2024-05-24 3:26 ` Nicolin Chen
2024-05-24 5:24 ` Tian, Kevin
2024-05-24 5:57 ` Nicolin Chen
2024-05-24 7:21 ` Tian, Kevin
2024-05-24 13:12 ` Jason Gunthorpe
2024-05-24 13:05 ` Jason Gunthorpe
2024-05-23 5:44 ` Tian, Kevin
2024-05-23 6:09 ` Nicolin Chen
2024-05-23 6:22 ` Tian, Kevin
2024-05-23 13:33 ` Jason Gunthorpe
2024-05-12 14:51 ` Jason Gunthorpe
2024-04-13 3:47 ` [PATCH RFCv1 08/14] iommufd: Add IOMMU_VIOMMU_SET_DEV_ID ioctl Nicolin Chen
2024-05-12 14:58 ` Jason Gunthorpe
2024-05-13 5:24 ` Nicolin Chen
2024-05-17 5:14 ` Nicolin Chen
2024-05-21 18:30 ` Jason Gunthorpe
2024-05-22 2:15 ` Nicolin Chen
2024-05-23 6:42 ` Tian, Kevin
2024-05-24 5:40 ` Nicolin Chen
2024-05-24 7:13 ` Tian, Kevin
2024-05-24 13:19 ` Jason Gunthorpe
2024-05-27 1:08 ` Tian, Kevin
2024-05-28 20:22 ` Nicolin Chen
2024-05-28 20:33 ` Nicolin Chen
2024-05-29 2:58 ` Tian, Kevin
2024-05-29 3:20 ` Nicolin Chen
2024-05-30 0:28 ` Tian, Kevin
2024-05-30 0:58 ` Nicolin Chen
2024-05-30 3:05 ` Tian, Kevin
2024-05-30 4:26 ` Nicolin Chen
2024-06-01 21:45 ` Jason Gunthorpe
2024-06-03 3:25 ` Nicolin Chen
2024-06-06 18:24 ` Jason Gunthorpe
2024-06-06 18:44 ` Nicolin Chen
2024-06-07 0:27 ` Jason Gunthorpe
2024-06-07 0:36 ` Tian, Kevin
2024-06-07 14:49 ` Jason Gunthorpe
2024-06-07 21:19 ` Nicolin Chen
2024-06-10 12:04 ` Jason Gunthorpe
2024-06-10 20:01 ` Nicolin Chen
2024-06-10 22:01 ` Jason Gunthorpe
2024-06-10 23:04 ` Nicolin Chen
2024-06-11 0:28 ` Jason Gunthorpe
2024-06-11 0:44 ` Nicolin Chen
2024-06-11 12:17 ` Jason Gunthorpe [this message]
2024-06-11 19:11 ` Nicolin Chen
2024-05-28 20:30 ` Nicolin Chen
2024-05-24 13:20 ` Jason Gunthorpe
2024-04-13 3:47 ` [PATCH RFCv1 09/14] iommufd/selftest: Add IOMMU_VIOMMU_SET_DEV_ID test coverage Nicolin Chen
2024-04-13 3:47 ` [PATCH RFCv1 10/14] iommufd/selftest: Add IOMMU_TEST_OP_MV_CHECK_DEV_ID Nicolin Chen
2024-04-13 3:47 ` [PATCH RFCv1 11/14] iommufd: Add struct iommufd_vqueue and its related viommu ops Nicolin Chen
2024-04-13 3:47 ` [PATCH RFCv1 12/14] iommufd: Add IOMMUFD_OBJ_VQUEUE and IOMMUFD_CMD_VQUEUE_ALLOC Nicolin Chen
2024-05-12 15:02 ` Jason Gunthorpe
2024-05-13 4:41 ` Nicolin Chen
2024-05-13 22:36 ` Jason Gunthorpe
2024-05-23 6:57 ` Tian, Kevin
2024-05-24 4:42 ` Nicolin Chen
2024-05-24 5:26 ` Tian, Kevin
2024-05-24 6:03 ` Nicolin Chen
2024-05-23 7:05 ` Tian, Kevin
2024-04-13 3:47 ` [PATCH RFCv1 13/14] iommufd: Add mmap infrastructure Nicolin Chen
2024-05-12 15:19 ` Jason Gunthorpe
2024-05-13 4:43 ` Nicolin Chen
2024-04-13 3:47 ` [PATCH RFCv1 14/14] iommu/tegra241-cmdqv: Add user-space use support Nicolin Chen
2024-05-22 8:40 ` [PATCH RFCv1 00/14] Add Tegra241 (Grace) CMDQV Support (part 2/2) Tian, Kevin
2024-05-22 16:48 ` Jason Gunthorpe
2024-05-22 19:47 ` Nicolin Chen
2024-05-22 23:28 ` Jason Gunthorpe
2024-05-22 23:43 ` Tian, Kevin
2024-05-23 3:09 ` Nicolin Chen
2024-05-23 12:48 ` Jason Gunthorpe
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