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Subject[RFC PATCH] 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 | 33 +++++++
drivers/vfio/pci/vfio_pci_private.h | 14 +++
drivers/vfio/pci/vfio_pci_rdwr.c | 165 ++++++++++++++++++++++++++++++++---
include/uapi/linux/vfio.h | 24 +++++
4 files changed, 224 insertions(+), 12 deletions(-)

diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c
index f041b1a6cf66..c8e7297a61a3 100644
--- a/drivers/vfio/pci/vfio_pci.c
+++ b/drivers/vfio/pci/vfio_pci.c
@@ -302,6 +302,7 @@ 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 */
@@ -311,6 +312,14 @@ 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->virq_disabled = false;

for (i = 0; i < vdev->num_regions; i++)
@@ -1039,6 +1048,28 @@ 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;
@@ -1217,6 +1248,8 @@ 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..23797622396e 100644
--- a/drivers/vfio/pci/vfio_pci_private.h
+++ b/drivers/vfio/pci/vfio_pci_private.h
@@ -29,6 +29,15 @@
#define PCI_CAP_ID_INVALID 0xFF /* default raw access */
#define PCI_CAP_ID_INVALID_VIRT 0xFE /* default virt access */

+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;
@@ -95,6 +104,8 @@ struct vfio_pci_device {
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 +131,9 @@ 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 357243d76f10..55bb4517d4ba 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"
@@ -113,6 +114,30 @@ static ssize_t do_io_rw(void __iomem *io, char __user *buf,
return done;
}

+static int vfio_pci_setup_barmap(struct vfio_pci_device *vdev, int bar)
+{
+ struct pci_dev *pdev = vdev->pdev;
+ int ret;
+ void __iomem *io;
+
+ if (vdev->barmap[bar])
+ return 0;
+
+ ret = pci_request_selected_regions(pdev, 1 << bar, "vfio");
+ if (ret)
+ return ret;
+
+ io = pci_iomap(pdev, bar, 0);
+ if (!io) {
+ pci_release_selected_regions(pdev, 1 << bar);
+ return -ENOMEM;
+ }
+
+ vdev->barmap[bar] = io;
+
+ return 0;
+}
+
ssize_t vfio_pci_bar_rw(struct vfio_pci_device *vdev, char __user *buf,
size_t count, loff_t *ppos, bool iswrite)
{
@@ -147,22 +172,13 @@ ssize_t vfio_pci_bar_rw(struct vfio_pci_device *vdev, char __user *buf,
if (!io)
return -ENOMEM;
x_end = end;
- } else if (!vdev->barmap[bar]) {
- int ret;
-
- ret = pci_request_selected_regions(pdev, 1 << bar, "vfio");
+ } else {
+ int ret = vfio_pci_setup_barmap(vdev, bar);
if (ret)
return ret;

- io = pci_iomap(pdev, bar, 0);
- if (!io) {
- pci_release_selected_regions(pdev, 1 << bar);
- return -ENOMEM;
- }
-
- vdev->barmap[bar] = io;
- } else
io = vdev->barmap[bar];
+ }

if (bar == vdev->msix_bar) {
x_start = vdev->msix_offset;
@@ -242,3 +258,128 @@ ssize_t vfio_pci_vga_rw(struct vfio_pci_device *vdev, char __user *buf,

return done;
}
+
+static int vfio_pci_ioeventfd_handler8(void *opaque, void *data)
+{
+ iowrite8((unsigned long)data, opaque);
+ return 0;
+}
+
+static int vfio_pci_ioeventfd_handler16(void *opaque, void *data)
+{
+ iowrite16((unsigned long)data, opaque);
+ return 0;
+}
+
+static int vfio_pci_ioeventfd_handler32(void *opaque, void *data)
+{
+ iowrite32((unsigned long)data, opaque);
+ return 0;
+}
+
+#ifdef iowrite64
+static int vfio_pci_ioeventfd_handler64(void *opaque, void *data)
+{
+ iowrite64((unsigned long)data, opaque);
+ return 0;
+}
+#endif
+
+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 *, void *);
+ unsigned long val;
+
+ /* 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;
+ val = data;
+ break;
+ case 2:
+ handler = &vfio_pci_ioeventfd_handler16;
+ val = le16_to_cpu(data);
+ break;
+ case 4:
+ handler = &vfio_pci_ioeventfd_handler32;
+ val = le32_to_cpu(data);
+ break;
+#ifdef iowrite64
+ case 8:
+ handler = &vfio_pci_ioeventfd_handler64;
+ val = le64_to_cpu(data);
+ 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);
+ kfree(ioeventfd);
+ ret = 0;
+ } else
+ ret = -EEXIST;
+
+ goto out_unlock;
+ }
+ }
+
+ if (fd < 0) {
+ ret = -ENODEV;
+ 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[ioeventfd->bar] + ioeventfd->pos,
+ handler, NULL, (void *)val,
+ &ioeventfd->virqfd, fd);
+ if (ret) {
+ kfree(ioeventfd);
+ goto out_unlock;
+ }
+
+ list_add(&ioeventfd->next, &vdev->ioeventfds_list);
+
+out_unlock:
+ mutex_unlock(&vdev->ioeventfds_lock);
+
+ return ret;
+}
diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
index e3301dbd27d4..07966a5f0832 100644
--- a/include/uapi/linux/vfio.h
+++ b/include/uapi/linux/vfio.h
@@ -503,6 +503,30 @@ struct vfio_pci_hot_reset {

#define VFIO_DEVICE_PCI_HOT_RESET _IO(VFIO_TYPE, VFIO_BASE + 13)

+/**
+ * VFIO_DEVICE_IOEVENTFD - _IOW(VFIO_TYPE, VFIO_BASE + 14,
+ * 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.
+ *
+ * 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 + 14)
+
/* -------- API for Type1 VFIO IOMMU -------- */

/**
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