Hello Shameer, Yi,
On 10/31/25 11:50, Shameer Kolothum wrote:
From: Yi Liu <[email protected]>
If user wants to expose PASID capability in vIOMMU, then VFIO would also
report the PASID cap for this device if the underlying hardware supports
it as well.
As a start, this chooses to put the vPASID cap in the last 8 bytes of the
vconfig space. This is a choice in the good hope of no conflict with any
existing cap or hidden registers. For the devices that has hidden registers,
user should figure out a proper offset for the vPASID cap. This may require
an option for user to config it. Here we leave it as a future extension.
There are more discussions on the mechanism of finding the proper offset.
https://lore.kernel.org/kvm/bn9pr11mb5276318969a212ad0649c7be8c...@bn9pr11mb5276.namprd11.prod.outlook.com/
Since we add a check to ensure the vIOMMU supports PASID, only devices
under those vIOMMUs can synthesize the vPASID capability. This gives
users control over which devices expose vPASID.
Signed-off-by: Yi Liu <[email protected]>
Tested-by: Zhangfei Gao <[email protected]>
Signed-off-by: Shameer Kolothum <[email protected]>
---
hw/vfio/pci.c | 37 +++++++++++++++++++++++++++++++++++++
include/hw/iommu.h | 1 +
2 files changed, 38 insertions(+)
diff --git a/hw/vfio/pci.c b/hw/vfio/pci.c
index 06b06afc2b..2054eac897 100644
--- a/hw/vfio/pci.c
+++ b/hw/vfio/pci.c
@@ -24,6 +24,7 @@
#include <sys/ioctl.h>
#include "hw/hw.h"
+#include "hw/iommu.h"
#include "hw/pci/msi.h"
#include "hw/pci/msix.h"
#include "hw/pci/pci_bridge.h"
@@ -2500,7 +2501,12 @@ static int vfio_setup_rebar_ecap(VFIOPCIDevice *vdev,
uint16_t pos)
static void vfio_add_ext_cap(VFIOPCIDevice *vdev)
{
+ HostIOMMUDevice *hiod = vdev->vbasedev.hiod;
+ HostIOMMUDeviceClass *hiodc = HOST_IOMMU_DEVICE_GET_CLASS(hiod);
PCIDevice *pdev = PCI_DEVICE(vdev);
+ uint64_t max_pasid_log2 = 0;
+ bool pasid_cap_added = false;
+ uint64_t hw_caps;
uint32_t header;
uint16_t cap_id, next, size;
uint8_t cap_ver;
@@ -2578,12 +2584,43 @@ static void vfio_add_ext_cap(VFIOPCIDevice *vdev)
pcie_add_capability(pdev, cap_id, cap_ver, next, size);
}
break;
+ case PCI_EXT_CAP_ID_PASID:
+ pasid_cap_added = true;
+ /* fallthrough */
default:
pcie_add_capability(pdev, cap_id, cap_ver, next, size);
}
}
+#ifdef CONFIG_IOMMUFD
The HostIOMMUDevice concept was introduced to abstract the use of
the Host IOMMU backends in VFIO (and other parts of QEMU):
- the VFIO IOMMU type1 backend, also referred as 'legacy',
- IOMMUFD
Adding code in VFIO under CONFIG_IOMMUFD should be avoided always
when possible. There are exceptions, such as for the definition
of the properties below in this file. This is, however, due to the
dual-bus nature of the VFIO devices and the limitation of QEMU class
inheritance.
In this case, I think we can extend HostIOMMUDevice and associated
class, to handle PASID support. Please rework this patch. I can
merge as a prereq change.
Also, IOMMUFD backend is not supported on all platforms, so these
changes, even if correct, won't compile.
Thanks,
C.
+ /*
+ * Although we check for PCI_EXT_CAP_ID_PASID above, the Linux VFIO
+ * framework currently hides this capability. Try to retrieve it
+ * through alternative kernel interfaces (e.g. IOMMUFD APIs).
+ */
+ if (!pasid_cap_added && hiodc->get_cap) {
+ hiodc->get_cap(hiod, HOST_IOMMU_DEVICE_CAP_GENERIC_HW, &hw_caps, NULL);
+ hiodc->get_cap(hiod, HOST_IOMMU_DEVICE_CAP_MAX_PASID_LOG2,
+ &max_pasid_log2, NULL);
+ }
+
+ /*
+ * If supported, adds the PASID capability in the end of the PCIe config
+ * space. TODO: Add option for enabling pasid at a safe offset.
+ */
+ if (max_pasid_log2 && (pci_device_get_viommu_flags(pdev) &
+ VIOMMU_FLAG_PASID_SUPPORTED)) {
+ bool exec_perm = (hw_caps & IOMMU_HW_CAP_PCI_PASID_EXEC) ? true :
false;
+ bool priv_mod = (hw_caps & IOMMU_HW_CAP_PCI_PASID_PRIV) ? true : false;
+
+ pcie_pasid_init(pdev, PCIE_CONFIG_SPACE_SIZE -
PCI_EXT_CAP_PASID_SIZEOF,
+ max_pasid_log2, exec_perm, priv_mod);
+ /* PASID capability is fully emulated by QEMU */
+ memset(vdev->emulated_config_bits + pdev->exp.pasid_cap, 0xff, 8);
+ }
+#endif
+
/* 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);
diff --git a/include/hw/iommu.h b/include/hw/iommu.h
index 9b8bb94fc2..9635770bee 100644
--- a/include/hw/iommu.h
+++ b/include/hw/iommu.h
@@ -20,6 +20,7 @@
enum viommu_flags {
/* vIOMMU needs nesting parent HWPT to create nested HWPT */
VIOMMU_FLAG_WANT_NESTING_PARENT = BIT_ULL(0),
+ VIOMMU_FLAG_PASID_SUPPORTED = BIT_ULL(1),
};
#endif /* HW_IOMMU_H */
