On 6/23/2026 10:01 AM, Shameer Kolothum Thodi wrote:
Yes, I agree it would be better to put this in an else statement after it is verified that ats cap is present.-----Original Message----- From: Nathan Chen<[email protected]> Sent: 23 June 2026 03:36 To:[email protected] Cc: Yi Liu<[email protected]>; Eric Auger<[email protected]>; Zhenzhong Duan<[email protected]>; Alex Williamson <[email protected]>; Cédric Le Goater<[email protected]>; Matt Ochs <[email protected]>; Nicolin Chen<[email protected]>; Shameer Kolothum Thodi<[email protected]>; Nathan Chen <[email protected]> Subject: [PATCH v3 2/2] vfio/pci: Add ats property From: Nathan Chen<[email protected]> Add an "ats" OnOffAuto property to vfio-pci. When the device has an ATS extended capability in config space but we should not expose it (ats=off, or ats=auto and kernel reports IOMMU_HW_CAP_PCI_ATS_NOT_SUPPORTED), mask the capability so the guest does not see it. If ATS is explicitly requested but not supported by the kernel, fail device realize. This aligns with the kernel's per-device effective ATS reporting and allows vfio-pci to mask ATS when the host kernel reports ATS as unsupported. Emit a warning when ats=on is requested but the physical device does not advertise ATS, since ATS cannot be exposed to the guest in this case. Suggested-by: Shameer Kolothum<[email protected]> Signed-off-by: Nathan Chen<[email protected]> --- hw/vfio/pci.h | 1 + hw/vfio/pci.c | 88 ++++++++++++++++++++++++++++++++++++++++++++++++--- 2 files changed, 85 insertions(+), 4 deletions(-) diff --git a/hw/vfio/pci.h b/hw/vfio/pci.h index c3a1f53d35..f2934f2d84 100644 --- a/hw/vfio/pci.h +++ b/hw/vfio/pci.h @@ -188,6 +188,7 @@ struct VFIOPCIDevice { bool clear_parent_atomics_on_exit; bool skip_vsc_check; uint16_t vpasid_cap_offset; + OnOffAuto ats; VFIODisplay *dpy; Notifier irqchip_change_notifier; VFIOPCICPR cpr; diff --git a/hw/vfio/pci.c b/hw/vfio/pci.c index 9c06b25e63..c0436b4c04 100644 --- a/hw/vfio/pci.c +++ b/hw/vfio/pci.c @@ -2546,10 +2546,58 @@ static bool vfio_pci_synthesize_pasid_cap(VFIOPCIDevice *vdev, Error **errp) return true; } -static void vfio_add_ext_cap(VFIOPCIDevice *vdev) +/* + * Determine whether ATS capability should be advertised for @vdev, based on + * whether it was enabled on the command line and whether it is supported + * according to the kernel. + * + * Store whether ATS capability should be advertised in @ats_needed. + * + * Returns false only when ats=on is explicitly requested but the kernel + * reports it is not supported. Returns true in all other cases. + */ +static bool vfio_pci_ats_requested_and_supported(VFIOPCIDevice *vdev, + bool *ats_needed, Error **errp) +{ + HostIOMMUDevice *hiod = vdev->vbasedev.hiod; + HostIOMMUDeviceClass *hiodc; + bool ats_supported; + *ats_needed = false; + + if (vdev->ats == ON_OFF_AUTO_OFF) { + return true; + } + + *ats_needed = true; + if (!hiod) { + return true; + } + hiodc = HOST_IOMMU_DEVICE_GET_CLASS(hiod); + if (!hiodc || !hiodc->support_ats) { + return true; + } + + ats_supported = hiodc->support_ats(hiod); + if (vdev->ats == ON_OFF_AUTO_ON && !ats_supported) { + error_setg(errp, "vfio-pci: ATS requested but not supported by kernel"); + *ats_needed = false; + return false; + } + + if (vdev->ats == ON_OFF_AUTO_AUTO && !ats_supported) { + warn_report("vfio-pci: host kernel reports ATS unsupported; " + "ATS capability will be masked"); + }This will be slightly misleading if dev doesn't have the ATS CAP at all. Isn't it? I think, the best place to do this warning is below where we know ats_cap_present is set or not. Thanks, Shameer
Thanks, Nathan>> +
+ *ats_needed = ats_supported; + return true; +} + +static void vfio_add_ext_cap(VFIOPCIDevice *vdev, bool ats_needed) { PCIDevice *pdev = PCI_DEVICE(vdev); bool pasid_cap_added = false; + bool ats_cap_present = false; Error *err = NULL; uint32_t header; uint16_t cap_id, next, size; @@ -2635,7 +2683,19 @@ static void vfio_add_ext_cap(VFIOPCIDevice *vdev) */ case PCI_EXT_CAP_ID_PASID: pasid_cap_added = true; - /* fallthrough */ + pcie_add_capability(pdev, cap_id, cap_ver, next, size); + break; + case PCI_EXT_CAP_ID_ATS: + ats_cap_present = true; + /* + * If ATS is requested and supported according to the kernel, add + * the ATS capability. If not supported according to the kernel or + * disabled on the qemu command line, omit the ATS cap. + */ + if (ats_needed) { + pcie_add_capability(pdev, cap_id, cap_ver, next, size); + } + break; default: pcie_add_capability(pdev, cap_id, cap_ver, next, size); } @@ -2646,6 +2706,11 @@ static void vfio_add_ext_cap(VFIOPCIDevice *vdev) error_report_err(err); } + if (ats_needed && !ats_cap_present) { + warn_report("vfio-pci: ats=on requested, but host device has no " + "ATS extended capability"); + } + /* Cleanup chain head ID if necessary */ if (pci_get_word(pdev->config + PCI_CONFIG_SPACE_SIZE) == 0xFFFF) { pci_set_word(pdev->config + PCI_CONFIG_SPACE_SIZE, 0); @@ -2657,6 +2722,7 @@ static void vfio_add_ext_cap(VFIOPCIDevice *vdev) bool vfio_pci_add_capabilities(VFIOPCIDevice *vdev, Error **errp) { PCIDevice *pdev = PCI_DEVICE(vdev); + bool ats_needed = false; if (!(pdev->config[PCI_STATUS] & PCI_STATUS_CAP_LIST) || !pdev->config[PCI_CAPABILITY_LIST]) { @@ -2667,7 +2733,11 @@ bool vfio_pci_add_capabilities(VFIOPCIDevice *vdev, Error **errp) return false; } - vfio_add_ext_cap(vdev); + if (!vfio_pci_ats_requested_and_supported(vdev, &ats_needed, errp)) { + return false; + } + + vfio_add_ext_cap(vdev, ats_needed); return true; } @@ -3815,6 +3885,7 @@ static const Property vfio_pci_properties[] = { DEFINE_PROP_BOOL("skip-vsc-check", VFIOPCIDevice, skip_vsc_check, true), DEFINE_PROP_UINT16("x-vpasid-cap-offset", VFIOPCIDevice, vpasid_cap_offset, 0), + DEFINE_PROP_ON_OFF_AUTO("ats", VFIOPCIDevice, ats, ON_OFF_AUTO_AUTO), }; static void vfio_pci_set_fd(Object *obj, const char *str, Error **errp) @@ -3966,13 +4037,22 @@ static void vfio_pci_class_init(ObjectClass *klass, const void *data) "destination when doing live " "migration of device state via " "multifd channels"); - object_class_property_set_description(klass, /* 11.0 */ + object_class_property_set_description(klass, /* 11.0 */ "x-vpasid-cap-offset", "PCIe extended configuration space offset at which to place a " "synthetic PASID extended capability when PASID is enabled via " "a vIOMMU. A value of 0 (default) places the capability at the " "end of the extended configuration space. The offset must be " "4-byte aligned and within the PCIe extended configuration space"); + object_class_property_set_description(klass, /* 11.1 */ + "ats", + "Control guest visibility of the ATS PCIe extended capability. " + "Valid values are on, off, and auto (default). " + "'off' always masks ATS. " + "'on' requires ATS support for the device and fails realize if the " + "host kernel reports ATS as unavailable for this device. " + "'auto' masks ATS only when the host kernel reports " + "ATS as unavailable"); } static const TypeInfo vfio_pci_info = { -- 2.43.0
