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Message-ID: <802eacfa-b29d-4589-bad8-a9665909cb1b@intel.com>
Date: Fri, 9 May 2025 17:32:04 +0800
From: Yi Liu <yi.l.liu@...el.com>
To: Wei Wang <wei.w.wang@...el.com>, <dwmw2@...radead.org>,
<baolu.lu@...ux.intel.com>, <kevin.tian@...el.com>, <jroedel@...e.de>,
<linux-kernel@...r.kernel.org>, <iommu@...ts.linux.dev>
Subject: Re: [PATCH v1 3/3] iommu/vt-d: Fix ATS support check for integrated
endpoints
On 2025/5/9 22:00, Wei Wang wrote:
> The VT-d spec states that "SATC reporting structure identifies devices
> that have address translation cache and that is validated per requirements
> described in the 'Device TLB in System-on-Chip (SoC) Integrated Devices'
> section. It is recommended that system software enable ATC for this
> device". It is possible for an integrated device to have PCI ATC
> capability implemented but not validated per the requirements, and thus
> not appear in the SATC structure as recommended for ATS enablement.
>
> The current implementation checks ATS support for integrated endpoints in
> two places. First, it verifies if the integrated endpoint device is listed
> in SATC. If not, it proceeds to the second check that always returns true
> for integrated devices. This could result in endpoint devices not
> recommended in SATC presenting "supported = true" to the caller.
>
> Add integrated_device_ats_supported() for the integrated device ATS check
> in a single location, which improves readability. The above issue is
> also fixed in the function via returning false in that case.
if it is a fix. A Fixes tag is needed.
> Signed-off-by: Wei Wang <wei.w.wang@...el.com>
> ---
> drivers/iommu/intel/iommu.c | 42 +++++++++++++++++++++++++------------
> 1 file changed, 29 insertions(+), 13 deletions(-)
>
> diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
> index 2778bfe14f36..39abcf4e0f8f 100644
> --- a/drivers/iommu/intel/iommu.c
> +++ b/drivers/iommu/intel/iommu.c
> @@ -2760,6 +2760,34 @@ static struct dmar_satc_unit *dmar_find_matched_satc_unit(struct pci_dev *dev)
> return satcu;
> }
>
> +static bool integrated_device_ats_supported(struct pci_dev *dev, struct intel_iommu *iommu)
> +{
> + struct dmar_satc_unit *satcu = dmar_find_matched_satc_unit(dev);
> +
> + /*
> + * This device supports ATS as it is in SATC table. When IOMMU is in
> + * legacy mode, enabling ATS is done automatically by HW for the device
> + * that requires ATS, hence OS should not enable this device ATS to
> + * avoid duplicated TLB invalidation.
> + */
> + if (satcu)
> + return !(satcu->atc_required && !sm_supported(iommu));
> +
> + /*
> + * The integrated device isn't enumerated in the SATC structure. For
> + * example, it has ATS PCI capability implemented but not validated per
> + * the requirements described in the VT-d specification, specifically
> + * in the "Device TLB in System-on-Chip (SoC) Integrated Devices"
> + * section. Therefore, it does not appear in the SATC structure. Return
> + * false in this case.
> + *
> + * On older machines that do not support SATC (i.e., no SATC structure
> + * present), ATS is considered to be "always" supported for integrated
> + * endpoints.
> + */
> + return !list_empty(&dmar_satc_units);
shouldn't it be "return list_empty(&dmar_satc_units);"?
> +}
> +
> static bool dmar_ats_supported(struct pci_dev *dev, struct intel_iommu *iommu)
> {
> int i;
> @@ -2769,25 +2797,13 @@ static bool dmar_ats_supported(struct pci_dev *dev, struct intel_iommu *iommu)
> struct device *tmp;
> struct acpi_dmar_atsr *atsr;
> struct dmar_atsr_unit *atsru;
> - struct dmar_satc_unit *satcu;
>
> dev = pci_physfn(dev);
> - satcu = dmar_find_matched_satc_unit(dev);
> - if (satcu)
> - /*
> - * This device supports ATS as it is in SATC table.
> - * When IOMMU is in legacy mode, enabling ATS is done
> - * automatically by HW for the device that requires
> - * ATS, hence OS should not enable this device ATS
> - * to avoid duplicated TLB invalidation.
> - */
> - return !(satcu->atc_required && !sm_supported(iommu));
>
> for (bus = dev->bus; bus; bus = bus->parent) {
> bridge = bus->self;
> - /* If it's an integrated device, allow ATS */
> if (!bridge)
> - return true;
> + return integrated_device_ats_supported(dev, iommu);
> /* Connected via non-PCIe: no ATS */
> if (!pci_is_pcie(bridge) ||
> pci_pcie_type(bridge) == PCI_EXP_TYPE_PCI_BRIDGE)
--
Regards,
Yi Liu
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