From: Jason Gunthorpe <jgg@nvidia.com>
To: Samiullah Khawaja <skhawaja@google.com>
Cc: Shameer Kolothum <skolothumtho@nvidia.com>,
iommu@lists.linux.dev, linux-kernel@vger.kernel.org,
joro@8bytes.org, will@kernel.org, robin.murphy@arm.com,
baolu.lu@linux.intel.com, kevin.tian@intel.com,
nicolinc@nvidia.com, nathanc@nvidia.com, mochs@nvidia.com,
kjaju@nvidia.com
Subject: Re: [PATCH 1/2] iommu: Add device ATS not supported capability
Date: Tue, 3 Mar 2026 19:28:35 -0400 [thread overview]
Message-ID: <20260303232835.GI972761@nvidia.com> (raw)
In-Reply-To: <p435ycx3b27d5gpzcli2kbp4eh36fq2ufgkft3hf3rqgqfx7i6@oql6hovzwkju>
On Tue, Mar 03, 2026 at 10:42:48PM +0000, Samiullah Khawaja wrote:
> On Tue, Mar 03, 2026 at 03:03:47PM +0000, Shameer Kolothum wrote:
> > PCIe ATS may be disabled by platform firmware, root complex limitations,
> > or kernel policy even when a device advertises the ATS capability in its
> > PCI configuration space.
> >
> > Add a new IOMMU_CAP_PCI_ATS_NOT_SUPPORTED capability to allow IOMMU
> > drivers to report the effective ATS decision for a device.
>
> nit: Maybe have IOMMU_CAP_PCI_ATS_SUPPORTED instead of the negative
> variant of the capability. As this will affect only new users who might
> check this capability so this does not really have to be negative.
It is deliberately negative for UAPI reasons.
Currently all userspace should assume ATS is supported.
The negative means new userspace that is sensitive will still work
correctly on old and new kernels that both return 0 as meaning ATS is
supported.
Perhaps this should be touched on in the commit message.
Jason
next prev parent reply other threads:[~2026-03-03 23:28 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-03-03 15:03 [PATCH 0/2] iommu: Report effective PCIe ATS support status Shameer Kolothum
2026-03-03 15:03 ` [PATCH 1/2] iommu: Add device ATS not supported capability Shameer Kolothum
2026-03-03 22:42 ` Samiullah Khawaja
2026-03-03 23:28 ` Jason Gunthorpe [this message]
2026-03-04 0:14 ` Samiullah Khawaja
2026-03-04 8:31 ` Shameer Kolothum Thodi
2026-03-13 16:47 ` Jason Gunthorpe
2026-03-13 16:48 ` Jason Gunthorpe
2026-03-13 16:55 ` Shameer Kolothum Thodi
2026-03-03 15:03 ` [PATCH 2/2] iommufd: Report ATS not supported status via IOMMU_GET_HW_INFO Shameer Kolothum
2026-03-04 0:17 ` Samiullah Khawaja
2026-03-13 16:50 ` Jason Gunthorpe
2026-03-13 16:57 ` Shameer Kolothum Thodi
2026-03-16 8:10 ` Tian, Kevin
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