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Subject[PATCH 3/3] vfio/pci: Add ioeventfd support
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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;
+#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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