RE: [PATCH v5 09/10] vfio/pci: Extend VFIO_DEVICE_GET_PCI_HOT_RESET_INFO for vfio device cdev

Liu, Yi L
2023-05-18T13:49:59Z

> From: Alex Williamson <alex.williamson@redhat.com>
> Sent: Thursday, May 18, 2023 6:02 AM
>
> On Sat, 13 May 2023 06:21:35 -0700
> Yi Liu <yi.l.liu@intel.com> wrote:
>
> > This makes VFIO_DEVICE_GET_PCI_HOT_RESET_INFO ioctl to use the iommufd_ctx
>
> s/makes/allows/?
>
> s/to//
>
> > of the cdev device to check the ownership of the other affected devices.
> >
> > This returns devid for each of the affected devices. If it is bound to the
> > iommufd_ctx of the cdev device, _INFO reports a valid devid > 0; If it is
> > not opened by the calling user, but it belongs to the same iommu_group of
> > a device that is bound to the iommufd_ctx of the cdev device, reports devid
> > value of 0; If the device is un-owned device, configured within a different
> > iommufd, or opened outside of the vfio device cdev API, the _INFO ioctl shall
> > report devid value of -1.
> >
> > devid >=0 doesn't block hot-reset as the affected devices are considered to
> > be owned, while devid == -1 will block the use of VFIO_DEVICE_PCI_HOT_RESET
> > outside of proof-of-ownership calling conventions (ie. via legacy group
> > accessed devices).
> >
> > This adds flag VFIO_PCI_HOT_RESET_FLAG_DEV_ID to tell the user devid is
> > returned in case of calling user get device fd from other software stack
>
> "other software stack"? I think this is trying to say something like:
>
> When VFIO_DEVICE_GET_PCI_HOT_RESET_INFO is called on an IOMMUFD
> managed device, the new flag VFIO_PCI_HOT_RESET_FLAG_DEV_ID is
> reported to indicate the values returned are IOMMUFD devids rather
> than group IDs as used when accessing vfio devices through the
> conventional vfio group interface. Additionally the flag
> VFIO_PCI_HOT_RESET_FLAG_DEV_ID_OWNED will be reported in this mode if
> all of the devices affected by the hot-reset are owned by either
> virtue of being directly bound to the same iommufd context as the
> calling device, or implicitly owned via a shared IOMMU group.

Yes. it is.

> > and adds flag VFIO_PCI_HOT_RESET_FLAG_DEV_ID_OWNED to tell user if all
> > the affected devices are owned, so user can know it without looping all
> > the returned devids.
> >
> > Suggested-by: Jason Gunthorpe <jgg@nvidia.com>
> > 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 | 52 ++++++++++++++++++++++++++++++--
> > include/uapi/linux/vfio.h | 46 +++++++++++++++++++++++++++-
> > 2 files changed, 95 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c
> > index 4df2def35bdd..57586be770af 100644
> > --- a/drivers/vfio/pci/vfio_pci_core.c
> > +++ b/drivers/vfio/pci/vfio_pci_core.c
> > @@ -27,6 +27,7 @@
> > #include <linux/vgaarb.h>
> > #include <linux/nospec.h>
> > #include <linux/sched/mm.h>
> > +#include <linux/iommufd.h>
> > #if IS_ENABLED(CONFIG_EEH)
> > #include <asm/eeh.h>
> > #endif
> > @@ -36,6 +37,10 @@
> > #define DRIVER_AUTHOR "Alex Williamson <alex.williamson@redhat.com>"
> > #define DRIVER_DESC "core driver for VFIO based PCI devices"
> >
> > +#ifdef CONFIG_IOMMUFD
> > +MODULE_IMPORT_NS(IOMMUFD);
> > +#endif
> > +
> > static bool nointxmask;
> > static bool disable_vga;
> > static bool disable_idle_d3;
> > @@ -776,6 +781,9 @@ struct vfio_pci_fill_info {
> > int max;
> > int cur;
> > struct vfio_pci_dependent_device *devices;
> > + struct vfio_device *vdev;
> > + bool devid:1;
> > + bool dev_owned:1;
> > };
> >
> > static int vfio_pci_fill_devs(struct pci_dev *pdev, void *data)
> > @@ -790,7 +798,37 @@ static int vfio_pci_fill_devs(struct pci_dev *pdev, void *data)
> > if (!iommu_group)
> > return -EPERM; /* Cannot reset non-isolated devices */
> >
> > - fill->devices[fill->cur].group_id = iommu_group_id(iommu_group);
> > + if (fill->devid) {
> > + struct iommufd_ctx *iommufd = vfio_iommufd_physical_ictx(fill->vdev);
> > + struct vfio_device_set *dev_set = fill->vdev->dev_set;
> > + struct vfio_device *vdev;
> > +
> > + /*
> > + * Report devid for the affected devices:
> > + * - valid devid > 0 for the devices that are bound with
> > + * the iommufd of the calling device.
> > + * - devid == 0 for the devices that have not been opened
> > + * but have same group with one of the devices bound to
> > + * the iommufd of the calling device.
> > + * - devid == -1 for others, and clear dev_owned flag.
> > + */
> > + vdev = vfio_find_device_in_devset(dev_set, &pdev->dev);
> > + if (vdev && iommufd == vfio_iommufd_physical_ictx(vdev)) {
> > + int ret;
> > +
> > + ret = vfio_iommufd_physical_devid(vdev);
> > + if (WARN_ON(ret < 0))
> > + return ret;
> > + fill->devices[fill->cur].devid = ret;
>
> Nit, @devid seems like a better variable name here rather than @ret.
>
> > + } else if (vdev && iommufd_ctx_has_group(iommufd, iommu_group)) {
> > + fill->devices[fill->cur].devid = VFIO_PCI_DEVID_OWNED;
> > + } else {
> > + fill->devices[fill->cur].devid = VFIO_PCI_DEVID_NOT_OWNED;
> > + fill->dev_owned = false;
> > + }
>
> I think we're not describing the requirements for this middle test
> correctly. We're essentially only stating the iommufd_ctx_has_group()
> part of the requirement, but we're also enforcing a
> vfio_find_device_in_devset() requirement, which means the device is not
> just unopened within a group shared by the iommufd context, but it must
> also still be a device registered as a member of the devset, ie. it
> must be bound to a vfio driver.

Yes. This is to make it be par with hot-reset path. This is needed. Is it?

>
> It's not a new requirement, it's imposed in the hot-reset ioctl itself,
> but it's new for the info ioctl given that it's now trying to report
> that the user can perform the reset for cdev callers.
>
> This also shares too much logic with vfio_device_owned() added in the
> next patch. I think it might be cleaner to move the iommu_group_get() to
> the group path below and change vfio_device_owned() to something that
> can be used here and in the reset path. For example, if we had a
> function like:
>
> static int vfio_hot_reset_devid(struct vfio_device *vdev,
> struct iommufd_ctx *iommufd_ctx)
> {
> struct iommu_group *group;
> int devid;
>
> if (!vdev)
> return VFIO_PCI_DEVID_NOT_OWNED;
>
> if (vfio_iommufd_physical_ictx(vdev) == iommufd_ctx)
> return vfio_iommufd_physical_devid(vdev);
>
> group = iommu_group_get(vdev->dev);
> if (!group)
> return VFIO_PCI_DEVID_NOT_OWNED;
>
> if (iommufd_ctx_has_group(iommufd_ctx, group))
> devid = VFIO_PCI_DEVID_OWNED;
>
> iommu_group_put(group);
>
> return devid;
> }

Thanks. This can be placed in vfio/iommufd.c, hence no need to
Import the IOMMUFD namespace in vfio_pci_core.c.
vfio_iommufd_physical_devid() can ebe static within vfio/iommufd.c

> It could be called above as:
>
> vdev = vfio_find_device_in_devset(dev_set, &pdev->dev);
> fill->devices[fill->cur].devid =
> vfio_hot_reset_devid(vdev, iommufd);
>
>
> And from vfio_pci_dev_set_hot_reset() as:
>
> bool owned;
>
> if (iommufd_ctx) {
> int devid = vfio_hot_reset_devid(&cur_vma->vdev,
> iommufd_ctx);
>
> owned = (devid != VFIO_PCI_DEVID_NOT_OWNED);
> } else
> owned = vfio_dev_in_groups(&cur_vma->vdev, groups);
>
> Any better?

Above looks good enough.

>
> > + } else {
> > + fill->devices[fill->cur].group_id = iommu_group_id(iommu_group);
> > + }
> > fill->devices[fill->cur].segment = pci_domain_nr(pdev->bus);
> > fill->devices[fill->cur].bus = pdev->bus->number;
> > fill->devices[fill->cur].devfn = pdev->devfn;
> > @@ -1229,17 +1267,27 @@ static int vfio_pci_ioctl_get_pci_hot_reset_info(
> > return -ENOMEM;
> >
> > fill.devices = devices;
> > + fill.vdev = &vdev->vdev;
> >
> > + mutex_lock(&vdev->vdev.dev_set->lock);
> > + fill.devid = fill.dev_owned = vfio_device_cdev_opened(&vdev->vdev);
> > ret = vfio_pci_for_each_slot_or_bus(vdev->pdev, vfio_pci_fill_devs,
> > &fill, slot);
> > + mutex_unlock(&vdev->vdev.dev_set->lock);
> >
> > /*
> > * If a device was removed between counting and filling, we may come up
> > * short of fill.max. If a device was added, we'll have a return of
> > * -EAGAIN above.
> > */
> > - if (!ret)
> > + if (!ret) {
> > hdr.count = fill.cur;
> > + if (fill.devid) {
> > + hdr.flags |= VFIO_PCI_HOT_RESET_FLAG_DEV_ID;
> > + if (fill.dev_owned)
> > + hdr.flags |=
> VFIO_PCI_HOT_RESET_FLAG_DEV_ID_OWNED;
> > + }
> > + }
>
> Does this clean up the flag and branching a bit?

Yes. 😊

>
> diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c
> index 737115d16a79..6a2a079e452d 100644
> --- a/drivers/vfio/pci/vfio_pci_core.c
> +++ b/drivers/vfio/pci/vfio_pci_core.c
> @@ -786,8 +786,7 @@ struct vfio_pci_fill_info {
> int cur;
> struct vfio_pci_dependent_device *devices;
> struct vfio_device *vdev;
> - bool devid:1;
> - bool dev_owned:1;
> + u32 flags;
> };
>
> static int vfio_pci_fill_devs(struct pci_dev *pdev, void *data)
> @@ -802,7 +801,7 @@ static int vfio_pci_fill_devs(struct pci_dev *pdev, void *data)
> if (!iommu_group)
> return -EPERM; /* Cannot reset non-isolated devices */
>
> - if (fill->devid) {
> + if (fill->flags & VFIO_PCI_HOT_RESET_FLAG_DEV_ID) {
> struct iommufd_ctx *iommufd = vfio_iommufd_physical_ictx(fill->vdev);
> struct vfio_device_set *dev_set = fill->vdev->dev_set;
> struct vfio_device *vdev;
> @@ -814,7 +813,7 @@ static int vfio_pci_fill_devs(struct pci_dev *pdev, void *data)
> * - devid == 0 for the devices that have not been opened
> * but have same group with one of the devices bound to
> * the iommufd of the calling device.
> - * - devid == -1 for others, and clear dev_owned flag.
> + * - devid == -1 for others, and clear owned flag.
> */
> vdev = vfio_find_device_in_devset(dev_set, &pdev->dev);
> if (vdev && iommufd == vfio_iommufd_physical_ictx(vdev)) {
> @@ -828,7 +827,7 @@ static int vfio_pci_fill_devs(struct pci_dev *pdev, void *data)
> fill->devices[fill->cur].devid = VFIO_PCI_DEVID_OWNED;
> } else {
> fill->devices[fill->cur].devid = VFIO_PCI_DEVID_NOT_OWNED;
> - fill->dev_owned = false;
> + fill->flags &= ~VFIO_PCI_HOT_RESET_FLAG_DEV_ID_OWNED;
> }
> } else {
> fill->devices[fill->cur].group_id = iommu_group_id(iommu_group);
> @@ -1273,8 +1272,11 @@ static int vfio_pci_ioctl_get_pci_hot_reset_info(
> fill.devices = devices;
> fill.vdev = &vdev->vdev;
>
> + if (vfio_device_cdev_opened(&vdev->vdev))
> + fill.flags |= VFIO_PCI_HOT_RESET_FLAG_DEV_ID |
> + VFIO_PCI_HOT_RESET_FLAG_DEV_ID_OWNED;
> +
> mutex_lock(&vdev->vdev.dev_set->lock);
> - fill.devid = fill.dev_owned = vfio_device_cdev_opened(&vdev->vdev);
> ret = vfio_pci_for_each_slot_or_bus(vdev->pdev, vfio_pci_fill_devs,
> &fill, slot);
> mutex_unlock(&vdev->vdev.dev_set->lock);
> @@ -1286,11 +1288,7 @@ static int vfio_pci_ioctl_get_pci_hot_reset_info(
> */
> if (!ret) {
> hdr.count = fill.cur;
> - if (fill.devid) {
> - hdr.flags |= VFIO_PCI_HOT_RESET_FLAG_DEV_ID;
> - if (fill.dev_owned)
> - hdr.flags |=
> VFIO_PCI_HOT_RESET_FLAG_DEV_ID_OWNED;
> - }
> + hdr.flags = fill.flags;
> }
>
> reset_info_exit:
>
> Thanks,
> Alex

Thanks,
Yi Liu

> >
> > reset_info_exit:
> > if (copy_to_user(arg, &hdr, minsz))
> > diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
> > index 0552e8dcf0cb..01203215251a 100644
> > --- a/include/uapi/linux/vfio.h
> > +++ b/include/uapi/linux/vfio.h
> > @@ -650,11 +650,53 @@ enum {
> > * VFIO_DEVICE_GET_PCI_HOT_RESET_INFO - _IOWR(VFIO_TYPE, VFIO_BASE + 12,
> > * struct vfio_pci_hot_reset_info)
> > *
> > + * This command is used to query the affected devices in the hot reset for
> > + * a given device.
> > + *
> > + * This command always reports the segment, bus, and devfn information for
> > + * each affected device, and selectively reports the group_id or devid per
> > + * the way how the calling device is opened.
> > + *
> > + * - If the calling device is opened via the traditional group/container
> > + * API, group_id is reported. User should check if it has owned all
> > + * the affected devices and provides a set of group fds to prove the
> > + * ownership in VFIO_DEVICE_PCI_HOT_RESET ioctl.
> > + *
> > + * - If the calling device is opened as a cdev, devid is reported.
> > + * Flag VFIO_PCI_HOT_RESET_FLAG_DEV_ID is set to indicate this
> > + * data type. For a given affected device, it is considered owned by
> > + * this interface if it meets the following conditions:
> > + * 1) Has a valid devid within the iommufd_ctx of the calling device.
> > + * Ownership cannot be determined across separate iommufd_ctx and the
> > + * cdev calling conventions do not support a proof-of-ownership model
> > + * as provided in the legacy group interface. In this case a valid
> > + * devid with value greater than zero is provided in the return
> > + * structure.
> > + * 2) Does not have a valid devid within the iommufd_ctx of the calling
> > + * device, but belongs to the same IOMMU group as the calling device
> > + * or another opened device that has a valid devid within the
> > + * iommufd_ctx of the calling device. This provides implicit ownership
> > + * for devices within the same DMA isolation context. In this case
> > + * the invalid devid value of zero is provided in the return structure.
> > + *
> > + * A devid value of -1 is provided in the return structure for devices
> > + * where ownership is not available. Such devices prevent the use of
> > + * VFIO_DEVICE_PCI_HOT_RESET outside of proof-of-ownership calling
> > + * conventions (ie. via legacy group accessed devices).
> > + * Flag VFIO_PCI_HOT_RESET_FLAG_DEV_ID_OWNED would be set when all the
> > + * affected devices are owned by the user. This flag is available only
> > + * when VFIO_PCI_HOT_RESET_FLAG_DEV_ID is set, otherwise reserved.
> > + *
> > * Return: 0 on success, -errno on failure:
> > * -enospc = insufficient buffer, -enodev = unsupported for device.
> > */
> > struct vfio_pci_dependent_device {
> > - __u32 group_id;
> > + union {
> > + __u32 group_id;
> > + __u32 devid;
> > +#define VFIO_PCI_DEVID_OWNED 0
> > +#define VFIO_PCI_DEVID_NOT_OWNED -1
> > + };
> > __u16 segment;
> > __u8 bus;
> > __u8 devfn; /* Use PCI_SLOT/PCI_FUNC */
> > @@ -663,6 +705,8 @@ struct vfio_pci_dependent_device {
> > struct vfio_pci_hot_reset_info {
> > __u32 argsz;
> > __u32 flags;
> > +#define VFIO_PCI_HOT_RESET_FLAG_DEV_ID (1 << 0)
> > +#define VFIO_PCI_HOT_RESET_FLAG_DEV_ID_OWNED (1 << 1)
> > __u32 count;
> > struct vfio_pci_dependent_device devices[];
> > };