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vfio/pci: Add ats property

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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.

Emit a warning when ats=auto, ats cap is present on the physical device,
but kernel reports ATS as unsupported.

Suggested-by: Shameer Kolothum <skolothumtho@nvidia.com>
Signed-off-by: Nathan Chen <nathanc@nvidia.com>
Reviewed-by: Shameer Kolothum <skolothumtho@nvidia.com>
Reviewed-by: Cédric Le Goater <clg@redhat.com>
Link: https://lore.kernel.org/qemu-devel/20260623204943.989903-3-nathanc@nvidia.com
Signed-off-by: Cédric Le Goater <clg@redhat.com>
This commit is contained in:
Nathan Chen
2026-06-23 13:49:42 -07:00
committed by Cédric Le Goater
parent 6befa55274
commit bc034e8a95
2 changed files with 85 additions and 4 deletions
Download Patch File Download Diff File Expand all files Collapse all files

88
hw/vfio/pci.c
View File

@@ -2548,10 +2548,53 @@ 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;
}
*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;
@@ -2637,7 +2680,19 @@ 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);
}
@@ -2648,6 +2703,16 @@ static void vfio_add_ext_cap(VFIOPCIDevice *vdev)
error_report_err(err);
}
if (vdev->ats == ON_OFF_AUTO_ON && !ats_cap_present) {
warn_report("vfio-pci: ats=on requested, but host device has no "
"ATS extended capability");
}
if (vdev->ats == ON_OFF_AUTO_AUTO && ats_cap_present && !ats_needed) {
warn_report("vfio-pci: host kernel reports ATS unsupported; "
"ATS capability will be masked");
}
/* 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);
@@ -2659,6 +2724,7 @@ 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]) {
@@ -2669,7 +2735,11 @@ 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;
}
@@ -3819,6 +3889,7 @@ 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)
@@ -3970,13 +4041,22 @@ 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 = {

1
hw/vfio/pci.h
View File

@@ -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;