vfio/pci: Add ioeventfd support

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.

Reviewed-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>

4 files changed, 192 insertions, 0 deletions

diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c
index b0f759476900..c6822149b394 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 @@ hot_reset_release:
 
                 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) {
@@ -1215,6 +1249,7 @@ static void vfio_pci_remove(struct pci_dev *pdev)
 
         vfio_iommu_group_put(pdev->dev.iommu_group, &pdev->dev);
         kfree(vdev->region);
+        mutex_destroy(&vdev->ioeventfds_lock);
         kfree(vdev);
 
         if (vfio_pci_is_vga(pdev)) {
diff --git a/drivers/vfio/pci/vfio_pci_private.h b/drivers/vfio/pci/vfio_pci_private.h
index f561ac1c78a0..cde3b5d3441a 100644
--- a/drivers/vfio/pci/vfio_pci_private.h
+++ b/drivers/vfio/pci/vfio_pci_private.h
@@ -29,6 +29,19 @@
 #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;
+        void __iomem            *addr;
+        uint64_t                data;
+        loff_t                  pos;
+        int                     bar;
+        int                     count;
+};
+
 struct vfio_pci_irq_ctx {
         struct eventfd_ctx      *trigger;
         struct virqfd           *unmask;
@@ -92,9 +105,12 @@ 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 +136,9 @@ 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..a6029d0a5524 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 +276,113 @@ ssize_t vfio_pci_vga_rw(struct vfio_pci_device *vdev, char __user *buf,
 
         return done;
 }
+
+static int vfio_pci_ioeventfd_handler(void *opaque, void *unused)
+{
+        struct vfio_pci_ioeventfd *ioeventfd = opaque;
+
+        switch (ioeventfd->count) {
+        case 1:
+                vfio_iowrite8(ioeventfd->data, ioeventfd->addr);
+                break;
+        case 2:
+                vfio_iowrite16(ioeventfd->data, ioeventfd->addr);
+                break;
+        case 4:
+                vfio_iowrite32(ioeventfd->data, ioeventfd->addr);
+                break;
+#ifdef iowrite64
+        case 8:
+                vfio_iowrite64(ioeventfd->data, ioeventfd->addr);
+                break;
+#endif
+        }
+
+        return 0;
+}
+
+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;
+
+        /* 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;
+
+#ifndef iowrite64
+        if (count == 8)
+                return -EINVAL;
+#endif
+
+        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->addr = vdev->barmap[bar] + pos;
+        ioeventfd->data = data;
+        ioeventfd->pos = pos;
+        ioeventfd->bar = bar;
+        ioeventfd->count = count;
+
+        ret = vfio_virqfd_enable(ioeventfd, vfio_pci_ioeventfd_handler,
+                                 NULL, NULL, &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..1aa7b82e8169 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, for all widths,
+ * or at all.  vfio-pci currently only enables support for BAR regions,
+ * excluding 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 -------- */
 
 /**