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

Alex Williamson
2023-05-18T20:03:18Z

On Thu, 18 May 2023 13:21:57 +0000
"Liu, Yi L" <yi.l.liu@intel.com> wrote:

> > 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?

Yes. In supporting this null-array model, the kernel is taking on the
responsibility to indicate that the hot-reset is available, which
necessarily includes the devset test. I think the logic we have is
correct, but the documentation and comments should match the code as
well.

> > 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

Good, that's an improvement too. Thanks,

Alex

> > 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[];
> > > };
>