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    SubjectRE: [PATCH 3/3] vfio: Report PASID capability via VFIO_DEVICE_FEATURE ioctl
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    >-----Original Message-----
    >From: Liu, Yi L <yi.l.liu@intel.com>
    >Sent: Monday, November 27, 2023 2:39 PM
    >Subject: [PATCH 3/3] vfio: Report PASID capability via VFIO_DEVICE_FEATURE
    >ioctl
    >
    >This reports the PASID capability data to userspace via VFIO_DEVICE_FEATURE,
    >hence userspace could probe PASID capability by it. This is a bit different
    >with other capabilities which are reported to userspace when the user reads
    >the device's PCI configuration space. There are two reasons for this.
    >
    > - First, Qemu by default exposes all available PCI capabilities in vfio-pci
    > config space to the guest as read-only, so adding PASID capability in the
    > vfio-pci config space will make it exposed to the guest automatically while
    > an old Qemu doesn't really support it.
    >
    > - Second, PASID capability does not exit on VFs (instead shares the cap of
    > the PF). Creating a virtual PASID capability in vfio-pci config space needs
    > to find a hole to place it, but doing so may require device specific
    > knowledge to avoid potential conflict with device specific registers like
    > hiden bits in VF config space. It's simpler by moving this burden to the
    > VMM instead of maintaining a quirk system in the kernel.
    >
    >Suggested-by: Alex Williamson <alex.williamson@redhat.com>
    >Signed-off-by: Yi Liu <yi.l.liu@intel.com>
    >---
    > drivers/vfio/pci/vfio_pci_core.c | 47 ++++++++++++++++++++++++++++++++
    > include/uapi/linux/vfio.h | 13 +++++++++
    > 2 files changed, 60 insertions(+)
    >
    >diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c
    >index 1929103ee59a..8038aa45500e 100644
    >--- a/drivers/vfio/pci/vfio_pci_core.c
    >+++ b/drivers/vfio/pci/vfio_pci_core.c
    >@@ -1495,6 +1495,51 @@ static int vfio_pci_core_feature_token(struct
    >vfio_device *device, u32 flags,
    > return 0;
    > }
    >
    >+static int vfio_pci_core_feature_pasid(struct vfio_device *device, u32 flags,
    >+ struct vfio_device_feature_pasid __user
    >*arg,
    >+ size_t argsz)
    >+{
    >+ struct vfio_pci_core_device *vdev =
    >+ container_of(device, struct vfio_pci_core_device, vdev);
    >+ struct vfio_device_feature_pasid pasid = { 0 };
    >+ struct pci_dev *pdev = vdev->pdev;
    >+ u32 capabilities = 0;
    >+ int ret;
    >+
    >+ /* We do not support SET of the PASID capability */
    >+ ret = vfio_check_feature(flags, argsz, VFIO_DEVICE_FEATURE_GET,
    >+ sizeof(pasid));
    >+ if (ret != 1)
    >+ return ret;
    >+
    >+ /*
    >+ * Needs go to PF if the device is VF as VF shares its PF's
    >+ * PASID Capability.
    >+ */
    >+ if (pdev->is_virtfn)
    >+ pdev = pci_physfn(pdev);
    >+
    >+ if (!pdev->pasid_enabled)
    >+ goto out;

    Does a PF bound to VFIO have pasid enabled by default?
    Isn't the guest kernel's responsibility to enable pasid cap of an assigned PF?

    Thanks
    Zhenzhong

    >+
    >+#ifdef CONFIG_PCI_PASID
    >+ pci_read_config_dword(pdev, pdev->pasid_cap + PCI_PASID_CAP,
    >+ &capabilities);
    >+#endif
    >+
    >+ if (capabilities & PCI_PASID_CAP_EXEC)
    >+ pasid.capabilities |= VFIO_DEVICE_PASID_CAP_EXEC;
    >+ if (capabilities & PCI_PASID_CAP_PRIV)
    >+ pasid.capabilities |= VFIO_DEVICE_PASID_CAP_PRIV;
    >+
    >+ pasid.width = (capabilities >> 8) & 0x1f;
    >+
    >+out:
    >+ if (copy_to_user(arg, &pasid, sizeof(pasid)))
    >+ return -EFAULT;
    >+ return 0;
    >+}
    >+
    > int vfio_pci_core_ioctl_feature(struct vfio_device *device, u32 flags,
    > void __user *arg, size_t argsz)
    > {
    >@@ -1508,6 +1553,8 @@ int vfio_pci_core_ioctl_feature(struct vfio_device
    >*device, u32 flags,
    > return vfio_pci_core_pm_exit(device, flags, arg, argsz);
    > case VFIO_DEVICE_FEATURE_PCI_VF_TOKEN:
    > return vfio_pci_core_feature_token(device, flags, arg, argsz);
    >+ case VFIO_DEVICE_FEATURE_PASID:
    >+ return vfio_pci_core_feature_pasid(device, flags, arg, argsz);
    > default:
    > return -ENOTTY;
    > }
    >diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
    >index 495193629029..8326faf8622b 100644
    >--- a/include/uapi/linux/vfio.h
    >+++ b/include/uapi/linux/vfio.h
    >@@ -1512,6 +1512,19 @@ struct vfio_device_feature_bus_master {
    > };
    > #define VFIO_DEVICE_FEATURE_BUS_MASTER 10
    >
    >+/**
    >+ * Upon VFIO_DEVICE_FEATURE_GET, return the PASID capability for the device.
    >+ * Zero width means no support for PASID.
    >+ */
    >+struct vfio_device_feature_pasid {
    >+ __u16 capabilities;
    >+#define VFIO_DEVICE_PASID_CAP_EXEC (1 << 0)
    >+#define VFIO_DEVICE_PASID_CAP_PRIV (1 << 1)
    >+ __u8 width;
    >+ __u8 __reserved;
    >+};
    >+#define VFIO_DEVICE_FEATURE_PASID 11
    >+
    > /* -------- API for Type1 VFIO IOMMU -------- */
    >
    > /**
    >--
    >2.34.1

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