From: Nicolin Chen <nicolinc@nvidia•com>
To: Pranjal Shrivastava <praan@google•com>
Cc: <iommu@lists•linux.dev>, <linux-pci@vger•kernel.org>,
<linux-arm-kernel@lists•infradead.org>,
<linux-kernel@vger•kernel.org>, "Joerg Roedel" <joro@8bytes•org>,
Will Deacon <will@kernel•org>,
Bjorn Helgaas <bhelgaas@google•com>,
David Woodhouse <dwmw2@infradead•org>,
Lu Baolu <baolu.lu@linux•intel.com>,
Robin Murphy <robin.murphy@arm•com>,
"Suravee Suthikulpanit" <suravee.suthikulpanit@amd•com>,
Jason Gunthorpe <jgg@ziepe•ca>,
David Matlack <dmatlack@google•com>,
Samiullah Khawaja <skhawaja@google•com>,
Daniel Mentz <danielmentz@google•com>,
Pasha Tatashin <pasha.tatashin@soleen•com>,
Mostafa Saleh <smostafa@google•com>,
"Jason Gunthorpe" <jgg@nvidia•com>
Subject: Re: [PATCH v4 2/5] PCI/ATS: Validate STU for VFs in pci_prepare_ats()
Date: Mon, 25 May 2026 12:46:53 -0700 [thread overview]
Message-ID: <ahSnLeKchpPbz1m9@Asurada-Nvidia> (raw)
In-Reply-To: <20260525184347.4059549-3-praan@google.com>
On Mon, May 25, 2026 at 06:43:44PM +0000, Pranjal Shrivastava wrote:
> While every PCI Function that implements ATS has an independent ATS
> Extended Capability structure with a Read/Write Smallest Translation
> Unit (STU) field, the kernel manages SR-IOV ATS by requiring the IOMMU
> driver to configure the STU on the Physical Function (PF) before any
> any Virtual Functions (VFs) are created.
>
> Currently, pci_prepare_ats() bails out early for VFs, assuming that the
> PF has already been correctly prepared. However, this creates a potential
> mismatch if a VF is subsequently prepared with a different page shift.
>
> Update pci_prepare_ats() to validate that the requested page shift (ps)
> matches the STU already configured in the associated PF. This ensures
> early detection of incompatible configurations and maintains the kernel's
> policy of consistent STU sizing across all functions associated with a
> given SMMU.
>
> Reviewed-by: Jason Gunthorpe <jgg@nvidia•com>
> Reviewed-by: Samiullah Khawaja <skhawaja@google•com>
> Signed-off-by: Pranjal Shrivastava <praan@google•com>
Reviewed-by: Nicolin Chen <nicolinc@nvidia•com>
Nit:
> @@ -73,8 +73,13 @@ int pci_prepare_ats(struct pci_dev *dev, int ps)
> if (ps < PCI_ATS_MIN_STU)
> return -EINVAL;
>
> - if (dev->is_virtfn)
> + if (dev->is_virtfn) {
> + struct pci_dev *pdev = pci_physfn(dev);
> +
> + if (pdev->ats_stu != ps)
> + return -EINVAL;
> return 0;
> + }
pdev doesn't seem useful. Dropping it reads better to me:
if (pci_physfn(dev)->ats_stu != ps)
return -EINVAL;
Nicolin
next prev parent reply other threads:[~2026-05-25 19:47 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-05-25 18:43 [PATCH v4 0/5] iommu: Standardize ATS robustness and state tracking Pranjal Shrivastava
2026-05-25 18:43 ` [PATCH v4 1/5] PCI/ATS: Ensure pci_ats_supported() is PF-aware for VFs Pranjal Shrivastava
2026-05-25 19:42 ` Nicolin Chen
2026-05-25 18:43 ` [PATCH v4 2/5] PCI/ATS: Validate STU for VFs in pci_prepare_ats() Pranjal Shrivastava
2026-05-25 19:46 ` Nicolin Chen [this message]
2026-05-28 20:27 ` Pranjal Shrivastava
2026-05-25 18:43 ` [PATCH v4 3/5] iommu/arm-smmu-v3: Fix ATS state tracking Pranjal Shrivastava
2026-05-25 20:05 ` Nicolin Chen
2026-05-25 20:30 ` Pranjal Shrivastava
2026-05-25 20:40 ` Nicolin Chen
2026-05-25 18:43 ` [PATCH v4 4/5] iommu/vt-d: Fail probe on ATS configuration failure Pranjal Shrivastava
2026-05-25 18:43 ` [PATCH v4 5/5] iommu/amd: " Pranjal Shrivastava
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