From: Jason Gunthorpe <jgg@nvidia.com>
To: Robin Murphy <robin.murphy@arm.com>
Cc: Joerg Roedel <joro@8bytes.org>,
Vasant Hegde <vasant.hegde@amd.com>,
iommu@lists.linux.dev, suravee.suthikulpanit@amd.com
Subject: Re: [PATCH v3 0/9] iommu/amd: Add Generic IO Page Table Framework Support for v2 Page Table
Date: Thu, 8 Sep 2022 10:58:57 -0300 [thread overview]
Message-ID: <Yxn1IcWk+61ddiCn@nvidia.com> (raw)
In-Reply-To: <c48211fe-00b1-e679-21b8-00a85bba599a@arm.com>
On Thu, Sep 08, 2022 at 02:47:11PM +0100, Robin Murphy wrote:
> On 2022-09-08 14:30, Joerg Roedel wrote:
> > On Thu, Sep 08, 2022 at 10:19:18AM -0300, Jason Gunthorpe wrote:
> > > What is the use case for having PASID nested under another level of
> > > translation?
> >
> > Virtualization. Basically having a device access process address spaces
> > inside a virtual machine. That got never put into code, but it was the
> > rationale behind it.
>
> For SMMUv3 it did actually get as far as a prototype[1] before the iommufd
> work interjected. I believe there are cloud vendors using those patches in
> their deployments :O
This is a bit different, this is just normal nested translation stuff.
AMD decision has effectively nested the PASID under the RID, while
typically nested translation nests PASID and RID equally under a
parent table.
I can't think of a use case for nesting the PASID under the RID, in
every scenario this seems to be problematic. Glad to see it is undone
with the new HW.
Jason
next prev parent reply other threads:[~2022-09-08 13:59 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-08-25 6:39 [PATCH v3 0/9] iommu/amd: Add Generic IO Page Table Framework Support for v2 Page Table Vasant Hegde
2022-08-25 6:39 ` [PATCH v3 1/9] iommu/amd/io-pgtable: Implement map_pages io_pgtable_ops callback Vasant Hegde
2022-08-25 6:39 ` [PATCH v3 2/9] iommu/amd/io-pgtable: Implement unmap_pages " Vasant Hegde
2022-08-25 6:39 ` [PATCH v3 3/9] iommu/amd: Add map/unmap_pages() iommu_domain_ops callback support Vasant Hegde
2022-08-25 6:39 ` [PATCH v3 4/9] iommu/amd: Refactor amd_iommu_domain_enable_v2 to remove locking Vasant Hegde
2022-08-25 6:39 ` [PATCH v3 5/9] iommu/amd: Update sanity check when enable PRI/ATS for IOMMU v1 table Vasant Hegde
2022-08-25 6:39 ` [PATCH v3 6/9] iommu/amd: Initial support for AMD IOMMU v2 page table Vasant Hegde
2022-08-25 6:39 ` [PATCH v3 7/9] iommu/amd: Add support for Guest IO protection Vasant Hegde
2022-08-25 6:39 ` [PATCH v3 8/9] iommu/amd: Add support for using AMD IOMMU v2 page table for DMA-API Vasant Hegde
2022-08-25 6:39 ` [PATCH v3 9/9] iommu/amd: Add command-line option to enable different page table Vasant Hegde
2022-09-05 11:39 ` [PATCH v3 0/9] iommu/amd: Add Generic IO Page Table Framework Support for v2 Page Table Vasant Hegde
2022-09-06 16:35 ` Robin Murphy
2022-09-07 14:16 ` Joerg Roedel
2022-09-07 16:52 ` Jason Gunthorpe
2022-09-07 18:16 ` Robin Murphy
2022-09-08 0:12 ` Jason Gunthorpe
2022-09-08 12:20 ` Joerg Roedel
2022-09-08 12:53 ` Robin Murphy
2022-09-08 13:19 ` Jason Gunthorpe
2022-09-08 13:30 ` Joerg Roedel
2022-09-08 13:47 ` Robin Murphy
2022-09-08 13:58 ` Jason Gunthorpe [this message]
2022-09-08 15:23 ` Robin Murphy
2022-09-09 1:24 ` Baolu Lu
2022-09-09 7:51 ` Tian, Kevin
2022-09-07 14:14 ` Joerg Roedel
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