From: Jason Gunthorpe <jgg@nvidia.com>
To: Will Deacon <will@kernel.org>
Cc: Robin Murphy <robin.murphy@arm.com>,
Nicolin Chen <nicolinc@nvidia.com>,
bhelgaas@google.com, joro@8bytes.org, praan@google.com,
baolu.lu@linux.intel.com, kevin.tian@intel.com,
miko.lenczewski@arm.com, linux-arm-kernel@lists.infradead.org,
iommu@lists.linux.dev, linux-kernel@vger.kernel.org,
linux-pci@vger.kernel.org
Subject: Re: [PATCH RFCv1 3/3] iommu/arm-smmu-v3: Allow ATS to be always on
Date: Tue, 27 Jan 2026 10:49:04 -0400 [thread overview]
Message-ID: <20260127144904.GE1134360@nvidia.com> (raw)
In-Reply-To: <aXjCvuBFCDBi7jUD@willie-the-truck>
On Tue, Jan 27, 2026 at 01:50:54PM +0000, Will Deacon wrote:
> Argh, I had conflated a transaction using SSID 0 vs a transaction
> without a substream at all. So I think this makes sense now...
Yeah, it is bit subtle, but as a SW choice the iommu subsystem
reserves PASID 0/SSID 0 as the "untagged" translation.
Several HW's force this in their implementation (ie AMD)
ARM however includes a "Substream Valid" in the input bus. Linux
doesn't use the combination "Substream Valid, SSID=0", that should
never occur.
If it wrongly does happen then IDENTITY will generate a fault, either
C_BAD_CD (due to it being non-valid) or C_BAD_SUBSTREAMID (due to
S1CDMax disabling substreams).
While PAGING will either fault with C_BAD_SUBSTREAMID (S2 paging
domain) or success when S1DSS=b10.
Jason
next prev parent reply other threads:[~2026-01-27 14:49 UTC|newest]
Thread overview: 60+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-01-17 4:56 [PATCH RFCv1 0/3] Allow ATS to be always on for certain ATS-capable devices Nicolin Chen
2026-01-17 4:56 ` [PATCH RFCv1 1/3] PCI: Allow ATS to be always on for CXL.cache capable devices Nicolin Chen
2026-01-19 17:58 ` Jason Gunthorpe
2026-01-21 8:01 ` Tian, Kevin
2026-01-21 10:03 ` Jonathan Cameron
2026-01-21 13:03 ` Jason Gunthorpe
2026-01-22 1:17 ` Baolu Lu
2026-01-22 13:15 ` Jason Gunthorpe
2026-01-22 5:44 ` dan.j.williams
2026-01-22 13:14 ` Jason Gunthorpe
2026-01-22 16:29 ` Nicolin Chen
2026-01-22 16:58 ` Jason Gunthorpe
2026-01-22 19:46 ` dan.j.williams
2026-01-27 8:10 ` Tian, Kevin
2026-01-27 15:04 ` Jason Gunthorpe
2026-01-28 0:49 ` dan.j.williams
2026-01-28 13:05 ` Jason Gunthorpe
2026-02-03 5:13 ` Nicolin Chen
2026-02-03 14:33 ` Jason Gunthorpe
2026-02-03 17:45 ` Nicolin Chen
2026-02-03 17:55 ` Jason Gunthorpe
2026-02-03 18:50 ` Nicolin Chen
2026-02-04 13:21 ` Jason Gunthorpe
2026-02-03 18:59 ` Robin Murphy
2026-02-03 19:24 ` Nicolin Chen
2026-02-03 23:16 ` Jason Gunthorpe
2026-02-04 12:18 ` Robin Murphy
2026-02-04 13:20 ` Jason Gunthorpe
2026-02-18 22:56 ` Nicolin Chen
2026-02-19 14:37 ` Jason Gunthorpe
2026-02-19 16:53 ` Nicolin Chen
2026-02-19 17:41 ` Jason Gunthorpe
2026-02-20 4:52 ` Nicolin Chen
2026-02-20 12:50 ` Jason Gunthorpe
2026-02-20 13:22 ` Robin Murphy
2026-02-20 13:51 ` Jason Gunthorpe
2026-02-20 14:45 ` Robin Murphy
2026-02-26 15:10 ` Jason Gunthorpe
2026-02-20 18:49 ` Nicolin Chen
2026-02-24 14:38 ` Jason Gunthorpe
2026-01-28 0:57 ` Tian, Kevin
2026-01-28 13:11 ` Jason Gunthorpe
2026-01-29 3:28 ` Tian, Kevin
2026-01-22 10:24 ` Alejandro Lucero Palau
2026-01-17 4:56 ` [PATCH RFCv1 2/3] PCI: Allow ATS to be always on for non-CXL NVIDIA GPUs Nicolin Chen
2026-01-19 18:00 ` Jason Gunthorpe
2026-01-19 18:09 ` Nicolin Chen
2026-01-17 4:56 ` [PATCH RFCv1 3/3] iommu/arm-smmu-v3: Allow ATS to be always on Nicolin Chen
2026-01-19 20:06 ` Jason Gunthorpe
2026-01-26 12:39 ` Will Deacon
2026-01-26 17:20 ` Jason Gunthorpe
2026-01-26 18:40 ` Nicolin Chen
2026-01-26 19:16 ` Jason Gunthorpe
2026-01-26 18:49 ` Robin Murphy
2026-01-26 19:09 ` Jason Gunthorpe
2026-01-27 13:10 ` Will Deacon
2026-01-27 13:26 ` Robin Murphy
2026-01-27 13:50 ` Will Deacon
2026-01-27 14:49 ` Jason Gunthorpe [this message]
2026-01-26 18:21 ` Nicolin Chen
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