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SubjectRe: [PATCH 3/3] vfio/pci: Add ioeventfd support
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Hi Alex,

On 28/02/18 21:15, Alex Williamson wrote:
> The ioeventfd here is actually irqfd handling of an ioeventfd such as
> supported in KVM. A user is able to pre-program a device write to
> occur when the eventfd triggers. This is yet another instance of
> eventfd-irqfd triggering between KVM and vfio. The impetus for this
> is high frequency writes to pages which are virtualized in QEMU.
> Enabling this near-direct write path for selected registers within
> the virtualized page can improve performance and reduce overhead.
> Specifically this is initially targeted at NVIDIA graphics cards where
> the driver issues a write to an MMIO register within a virtualized
> region in order to allow the MSI interrupt to re-trigger.
>
> Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
> ---
> drivers/vfio/pci/vfio_pci.c | 34 ++++++++++
> drivers/vfio/pci/vfio_pci_private.h | 18 +++++
> drivers/vfio/pci/vfio_pci_rdwr.c | 115 +++++++++++++++++++++++++++++++++++
> include/uapi/linux/vfio.h | 27 ++++++++
> 4 files changed, 194 insertions(+)
>
> diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c
> index b0f759476900..ad18ed266dc0 100644
> --- a/drivers/vfio/pci/vfio_pci.c
> +++ b/drivers/vfio/pci/vfio_pci.c
> @@ -305,6 +305,7 @@ static void vfio_pci_disable(struct vfio_pci_device *vdev)
> {
> struct pci_dev *pdev = vdev->pdev;
> struct vfio_pci_dummy_resource *dummy_res, *tmp;
> + struct vfio_pci_ioeventfd *ioeventfd, *ioeventfd_tmp;
> int i, bar;
>
> /* Stop the device from further DMA */
> @@ -314,6 +315,15 @@ static void vfio_pci_disable(struct vfio_pci_device *vdev)
> VFIO_IRQ_SET_ACTION_TRIGGER,
> vdev->irq_type, 0, 0, NULL);
>
> + /* Device closed, don't need mutex here */
> + list_for_each_entry_safe(ioeventfd, ioeventfd_tmp,
> + &vdev->ioeventfds_list, next) {
> + vfio_virqfd_disable(&ioeventfd->virqfd);
> + list_del(&ioeventfd->next);
> + kfree(ioeventfd);
> + }
> + vdev->ioeventfds_nr = 0;
> +
> vdev->virq_disabled = false;
>
> for (i = 0; i < vdev->num_regions; i++)
> @@ -1012,6 +1022,28 @@ static long vfio_pci_ioctl(void *device_data,
>
> kfree(groups);
> return ret;
> + } else if (cmd == VFIO_DEVICE_IOEVENTFD) {
> + struct vfio_device_ioeventfd ioeventfd;
> + int count;
> +
> + minsz = offsetofend(struct vfio_device_ioeventfd, fd);
> +
> + if (copy_from_user(&ioeventfd, (void __user *)arg, minsz))
> + return -EFAULT;
> +
> + if (ioeventfd.argsz < minsz)
> + return -EINVAL;
> +
> + if (ioeventfd.flags & ~VFIO_DEVICE_IOEVENTFD_SIZE_MASK)
> + return -EINVAL;
> +
> + count = ioeventfd.flags & VFIO_DEVICE_IOEVENTFD_SIZE_MASK;
> +
> + if (hweight8(count) != 1 || ioeventfd.fd < -1)
> + return -EINVAL;
> +
> + return vfio_pci_ioeventfd(vdev, ioeventfd.offset,
> + ioeventfd.data, count, ioeventfd.fd);
> }
>
> return -ENOTTY;
> @@ -1174,6 +1206,8 @@ static int vfio_pci_probe(struct pci_dev *pdev, const struct pci_device_id *id)
> vdev->irq_type = VFIO_PCI_NUM_IRQS;
> mutex_init(&vdev->igate);
> spin_lock_init(&vdev->irqlock);
> + mutex_init(&vdev->ioeventfds_lock);
> + INIT_LIST_HEAD(&vdev->ioeventfds_list);
>
> ret = vfio_add_group_dev(&pdev->dev, &vfio_pci_ops, vdev);
> if (ret) {
> diff --git a/drivers/vfio/pci/vfio_pci_private.h b/drivers/vfio/pci/vfio_pci_private.h
> index f561ac1c78a0..33a48c3ba11c 100644
> --- a/drivers/vfio/pci/vfio_pci_private.h
> +++ b/drivers/vfio/pci/vfio_pci_private.h
> @@ -29,6 +29,18 @@
> #define PCI_CAP_ID_INVALID 0xFF /* default raw access */
> #define PCI_CAP_ID_INVALID_VIRT 0xFE /* default virt access */
>
> +/* Cap maximum number of ioeventfds per device (arbitrary) */
> +#define VFIO_PCI_IOEVENTFD_MAX 1000
> +
> +struct vfio_pci_ioeventfd {
> + struct list_head next;
> + struct virqfd *virqfd;
> + loff_t pos;
> + uint64_t data;
> + int bar;
> + int count;
> +};
> +
> struct vfio_pci_irq_ctx {
> struct eventfd_ctx *trigger;
> struct virqfd *unmask;
> @@ -92,9 +104,12 @@ struct vfio_pci_device {
> bool nointx;
> struct pci_saved_state *pci_saved_state;
> int refcnt;
> + int ioeventfds_nr;
> struct eventfd_ctx *err_trigger;
> struct eventfd_ctx *req_trigger;
> struct list_head dummy_resources_list;
> + struct mutex ioeventfds_lock;
> + struct list_head ioeventfds_list;
> };
>
> #define is_intx(vdev) (vdev->irq_type == VFIO_PCI_INTX_IRQ_INDEX)
> @@ -120,6 +135,9 @@ extern ssize_t vfio_pci_bar_rw(struct vfio_pci_device *vdev, char __user *buf,
> extern ssize_t vfio_pci_vga_rw(struct vfio_pci_device *vdev, char __user *buf,
> size_t count, loff_t *ppos, bool iswrite);
>
> +extern long vfio_pci_ioeventfd(struct vfio_pci_device *vdev, loff_t offset,
> + uint64_t data, int count, int fd);
> +
> extern int vfio_pci_init_perm_bits(void);
> extern void vfio_pci_uninit_perm_bits(void);
>
> diff --git a/drivers/vfio/pci/vfio_pci_rdwr.c b/drivers/vfio/pci/vfio_pci_rdwr.c
> index 925419e0f459..43e4b5112337 100644
> --- a/drivers/vfio/pci/vfio_pci_rdwr.c
> +++ b/drivers/vfio/pci/vfio_pci_rdwr.c
> @@ -17,6 +17,7 @@
> #include <linux/pci.h>
> #include <linux/uaccess.h>
> #include <linux/io.h>
> +#include <linux/vfio.h>
> #include <linux/vgaarb.h>
>
> #include "vfio_pci_private.h"
> @@ -275,3 +276,117 @@ ssize_t vfio_pci_vga_rw(struct vfio_pci_device *vdev, char __user *buf,
>
> return done;
> }
> +
> +#define VFIO_PCI_IOEVENTFD_HANDLER(size) \
> +static int vfio_pci_ioeventfd_handler##size(void *opaque, void *data) \
> +{ \
> + vfio_iowrite##size((unsigned long)data, opaque); \
> + return 0; \
> +}
> +
> +#ifdef iowrite64
> +VFIO_PCI_IOEVENTFD_HANDLER(64)
> +#endif
> +VFIO_PCI_IOEVENTFD_HANDLER(32)
> +VFIO_PCI_IOEVENTFD_HANDLER(16)
> +VFIO_PCI_IOEVENTFD_HANDLER(8)
> +
> +long vfio_pci_ioeventfd(struct vfio_pci_device *vdev, loff_t offset,
> + uint64_t data, int count, int fd)
> +{
> + struct pci_dev *pdev = vdev->pdev;
> + loff_t pos = offset & VFIO_PCI_OFFSET_MASK;
> + int ret, bar = VFIO_PCI_OFFSET_TO_INDEX(offset);
> + struct vfio_pci_ioeventfd *ioeventfd;
> + int (*handler)(void *addr, void *value);
> +
> + /* Only support ioeventfds into BARs */
> + if (bar > VFIO_PCI_BAR5_REGION_INDEX)
> + return -EINVAL;
> +
> + if (pos + count > pci_resource_len(pdev, bar))
> + return -EINVAL;
> +
> + /* Disallow ioeventfds working around MSI-X table writes */
> + if (bar == vdev->msix_bar &&
> + !(pos + count <= vdev->msix_offset ||
> + pos >= vdev->msix_offset + vdev->msix_size))
> + return -EINVAL;
> +
> + switch (count) {
> + case 1:
> + handler = &vfio_pci_ioeventfd_handler8;
> + break;
> + case 2:
> + handler = &vfio_pci_ioeventfd_handler16;
> + break;
> + case 4:
> + handler = &vfio_pci_ioeventfd_handler32;
> + break;
> +#ifdef iowrite64
> + case 8:
> + handler = &vfio_pci_ioeventfd_handler64;
> + break;
from a user point of view, it is straightforward this setup will be
rejected? This is not documented in the uapi at the moment.

Thanks

Eric
> +#endif
> + default:
> + return -EINVAL;
> + }
> +
> + ret = vfio_pci_setup_barmap(vdev, bar);
> + if (ret)
> + return ret;
> +
> + mutex_lock(&vdev->ioeventfds_lock);
> +
> + list_for_each_entry(ioeventfd, &vdev->ioeventfds_list, next) {
> + if (ioeventfd->pos == pos && ioeventfd->bar == bar &&
> + ioeventfd->data == data && ioeventfd->count == count) {
> + if (fd == -1) {
> + vfio_virqfd_disable(&ioeventfd->virqfd);
> + list_del(&ioeventfd->next);
> + vdev->ioeventfds_nr--;
> + kfree(ioeventfd);
> + ret = 0;
> + } else
> + ret = -EEXIST;
> +
> + goto out_unlock;
> + }
> + }
> +
> + if (fd < 0) {
> + ret = -ENODEV;
> + goto out_unlock;
> + }
> +
> + if (vdev->ioeventfds_nr >= VFIO_PCI_IOEVENTFD_MAX) {
> + ret = -ENOSPC;
> + goto out_unlock;
> + }
> +
> + ioeventfd = kzalloc(sizeof(*ioeventfd), GFP_KERNEL);
> + if (!ioeventfd) {
> + ret = -ENOMEM;
> + goto out_unlock;
> + }
> +
> + ioeventfd->pos = pos;
> + ioeventfd->bar = bar;
> + ioeventfd->data = data;
> + ioeventfd->count = count;
> +
> + ret = vfio_virqfd_enable(vdev->barmap[bar] + pos, handler, NULL,
> + (void *)data, &ioeventfd->virqfd, fd);
> + if (ret) {
> + kfree(ioeventfd);
> + goto out_unlock;
> + }
> +
> + list_add(&ioeventfd->next, &vdev->ioeventfds_list);
> + vdev->ioeventfds_nr++;
> +
> +out_unlock:
> + mutex_unlock(&vdev->ioeventfds_lock);
> +
> + return ret;
> +}
> diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
> index c74372163ed2..7e9d76203e86 100644
> --- a/include/uapi/linux/vfio.h
> +++ b/include/uapi/linux/vfio.h
> @@ -575,6 +575,33 @@ struct vfio_device_gfx_plane_info {
>
> #define VFIO_DEVICE_GET_GFX_DMABUF _IO(VFIO_TYPE, VFIO_BASE + 15)
>
> +/**
> + * VFIO_DEVICE_IOEVENTFD - _IOW(VFIO_TYPE, VFIO_BASE + 16,
> + * struct vfio_device_ioeventfd)
> + *
> + * Perform a write to the device at the specified device fd offset, with
> + * the specified data and width when the provided eventfd is triggered.
> + * vfio bus drivers may not support this for all regions, or at all.
> + * vfio-pci currently only enables support for BAR regions and excludes
> + * the MSI-X vector table.
> + *
> + * Return: 0 on success, -errno on failure.
> + */
> +struct vfio_device_ioeventfd {
> + __u32 argsz;
> + __u32 flags;
> +#define VFIO_DEVICE_IOEVENTFD_8 (1 << 0) /* 1-byte write */
> +#define VFIO_DEVICE_IOEVENTFD_16 (1 << 1) /* 2-byte write */
> +#define VFIO_DEVICE_IOEVENTFD_32 (1 << 2) /* 4-byte write */
> +#define VFIO_DEVICE_IOEVENTFD_64 (1 << 3) /* 8-byte write */
> +#define VFIO_DEVICE_IOEVENTFD_SIZE_MASK (0xf)
> + __u64 offset; /* device fd offset of write */
> + __u64 data; /* data to be written */
> + __s32 fd; /* -1 for de-assignment */
> +};
> +
> +#define VFIO_DEVICE_IOEVENTFD _IO(VFIO_TYPE, VFIO_BASE + 16)
> +
> /* -------- API for Type1 VFIO IOMMU -------- */
>
> /**
>

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