Merge tag 'vfio-v4.17-rc1' of git://github.com/awilliam/linux-vfio

Pull VFIO updates from Alex Williamson:

 - Adopt iommu_unmap_fast() interface to type1 backend
   (Suravee Suthikulpanit)

 - mdev sample driver fixup (Shunyong Yang)

 - More efficient PFN mapping handling in type1 backend
   (Jason Cai)

 - VFIO device ioeventfd interface (Alex Williamson)

 - Tag new vfio-platform sub-maintainer (Alex Williamson)

* tag 'vfio-v4.17-rc1' of git://github.com/awilliam/linux-vfio:
  MAINTAINERS: vfio/platform: Update sub-maintainer
  vfio/pci: Add ioeventfd support
  vfio/pci: Use endian neutral helpers
  vfio/pci: Pull BAR mapping setup from read-write path
  vfio/type1: Improve memory pinning process for raw PFN mapping
  vfio-mdev/samples: change RDI interrupt condition
  vfio/type1: Adopt fast IOTLB flush interface when unmap IOVAs

7 files changed, 377 insertions, 43 deletions

diff --git a/MAINTAINERS b/MAINTAINERS
index 83f5a6fd7de3..7e48624f4f9f 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -14797,7 +14797,7 @@ F:	include/linux/mdev.h
 F:	samples/vfio-mdev/
 
 VFIO PLATFORM DRIVER
-M:	Baptiste Reynal <b.reynal@virtualopensystems.com>
+M:	Eric Auger <eric.auger@redhat.com>
 L:	kvm@vger.kernel.org
 S:	Maintained
 F:	drivers/vfio/platform/
diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c
index 8a1508a8e481..b423a309a6e0 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 +312,15 @@ 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++)
@@ -1009,6 +1019,28 @@ 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;
@@ -1171,6 +1203,8 @@ 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) {
@@ -1212,6 +1246,7 @@ 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 357243d76f10..a6029d0a5524 100644
--- a/drivers/vfio/pci/vfio_pci_rdwr.c
+++ b/drivers/vfio/pci/vfio_pci_rdwr.c
@@ -17,10 +17,29 @@
 #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"
 
+#ifdef __LITTLE_ENDIAN
+#define vfio_ioread64	ioread64
+#define vfio_iowrite64	iowrite64
+#define vfio_ioread32	ioread32
+#define vfio_iowrite32	iowrite32
+#define vfio_ioread16	ioread16
+#define vfio_iowrite16	iowrite16
+#else
+#define vfio_ioread64	ioread64be
+#define vfio_iowrite64	iowrite64be
+#define vfio_ioread32	ioread32be
+#define vfio_iowrite32	iowrite32be
+#define vfio_ioread16	ioread16be
+#define vfio_iowrite16	iowrite16be
+#endif
+#define vfio_ioread8	ioread8
+#define vfio_iowrite8	iowrite8
+
 /*
  * Read or write from an __iomem region (MMIO or I/O port) with an excluded
  * range which is inaccessible.  The excluded range drops writes and fills
@@ -44,15 +63,15 @@ static ssize_t do_io_rw(void __iomem *io, char __user *buf,
 			fillable = 0;
 
 		if (fillable >= 4 && !(off % 4)) {
-			__le32 val;
+			u32 val;
 
 			if (iswrite) {
 				if (copy_from_user(&val, buf, 4))
 					return -EFAULT;
 
-				iowrite32(le32_to_cpu(val), io + off);
+				vfio_iowrite32(val, io + off);
 			} else {
-				val = cpu_to_le32(ioread32(io + off));
+				val = vfio_ioread32(io + off);
 
 				if (copy_to_user(buf, &val, 4))
 					return -EFAULT;
@@ -60,15 +79,15 @@ static ssize_t do_io_rw(void __iomem *io, char __user *buf,
 
 			filled = 4;
 		} else if (fillable >= 2 && !(off % 2)) {
-			__le16 val;
+			u16 val;
 
 			if (iswrite) {
 				if (copy_from_user(&val, buf, 2))
 					return -EFAULT;
 
-				iowrite16(le16_to_cpu(val), io + off);
+				vfio_iowrite16(val, io + off);
 			} else {
-				val = cpu_to_le16(ioread16(io + off));
+				val = vfio_ioread16(io + off);
 
 				if (copy_to_user(buf, &val, 2))
 					return -EFAULT;
@@ -82,9 +101,9 @@ static ssize_t do_io_rw(void __iomem *io, char __user *buf,
 				if (copy_from_user(&val, buf, 1))
 					return -EFAULT;
 
-				iowrite8(val, io + off);
+				vfio_iowrite8(val, io + off);
 			} else {
-				val = ioread8(io + off);
+				val = vfio_ioread8(io + off);
 
 				if (copy_to_user(buf, &val, 1))
 					return -EFAULT;
@@ -113,6 +132,30 @@ 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 +190,13 @@ 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 +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/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
index 45657e2b1ff7..5c212bf29640 100644
--- a/drivers/vfio/vfio_iommu_type1.c
+++ b/drivers/vfio/vfio_iommu_type1.c
@@ -102,6 +102,13 @@ struct vfio_pfn {
 	atomic_t		ref_count;
 };
 
+struct vfio_regions {
+	struct list_head list;
+	dma_addr_t iova;
+	phys_addr_t phys;
+	size_t len;
+};
+
 #define IS_IOMMU_CAP_DOMAIN_IN_CONTAINER(iommu)	\
 					(!list_empty(&iommu->domain_list))
 
@@ -397,7 +404,6 @@ static long vfio_pin_pages_remote(struct vfio_dma *dma, unsigned long vaddr,
 {
 	unsigned long pfn = 0;
 	long ret, pinned = 0, lock_acct = 0;
-	bool rsvd;
 	dma_addr_t iova = vaddr - dma->vaddr + dma->iova;
 
 	/* This code path is only user initiated */
@@ -408,14 +414,23 @@ static long vfio_pin_pages_remote(struct vfio_dma *dma, unsigned long vaddr,
 	if (ret)
 		return ret;
 
+	if (is_invalid_reserved_pfn(*pfn_base)) {
+		struct vm_area_struct *vma;
+
+		down_read(&current->mm->mmap_sem);
+		vma = find_vma_intersection(current->mm, vaddr, vaddr + 1);
+		pinned = min_t(long, npage, vma_pages(vma));
+		up_read(&current->mm->mmap_sem);
+		return pinned;
+	}
+
 	pinned++;
-	rsvd = is_invalid_reserved_pfn(*pfn_base);
 
 	/*
 	 * Reserved pages aren't counted against the user, externally pinned
 	 * pages are already counted against the user.
 	 */
-	if (!rsvd && !vfio_find_vpfn(dma, iova)) {
+	if (!vfio_find_vpfn(dma, iova)) {
 		if (!lock_cap && current->mm->locked_vm + 1 > limit) {
 			put_pfn(*pfn_base, dma->prot);
 			pr_warn("%s: RLIMIT_MEMLOCK (%ld) exceeded\n", __func__,
@@ -435,13 +450,12 @@ static long vfio_pin_pages_remote(struct vfio_dma *dma, unsigned long vaddr,
 		if (ret)
 			break;
 
-		if (pfn != *pfn_base + pinned ||
-		    rsvd != is_invalid_reserved_pfn(pfn)) {
+		if (pfn != *pfn_base + pinned) {
 			put_pfn(pfn, dma->prot);
 			break;
 		}
 
-		if (!rsvd && !vfio_find_vpfn(dma, iova)) {
+		if (!vfio_find_vpfn(dma, iova)) {
 			if (!lock_cap &&
 			    current->mm->locked_vm + lock_acct + 1 > limit) {
 				put_pfn(pfn, dma->prot);
@@ -459,10 +473,8 @@ out:
 
 unpin_out:
 	if (ret) {
-		if (!rsvd) {
-			for (pfn = *pfn_base ; pinned ; pfn++, pinned--)
-				put_pfn(pfn, dma->prot);
-		}
+		for (pfn = *pfn_base ; pinned ; pfn++, pinned--)
+			put_pfn(pfn, dma->prot);
 
 		return ret;
 	}
@@ -660,11 +672,102 @@ unpin_exit:
 	return i > npage ? npage : (i > 0 ? i : -EINVAL);
 }
 
+static long vfio_sync_unpin(struct vfio_dma *dma, struct vfio_domain *domain,
+				struct list_head *regions)
+{
+	long unlocked = 0;
+	struct vfio_regions *entry, *next;
+
+	iommu_tlb_sync(domain->domain);
+
+	list_for_each_entry_safe(entry, next, regions, list) {
+		unlocked += vfio_unpin_pages_remote(dma,
+						    entry->iova,
+						    entry->phys >> PAGE_SHIFT,
+						    entry->len >> PAGE_SHIFT,
+						    false);
+		list_del(&entry->list);
+		kfree(entry);
+	}
+
+	cond_resched();
+
+	return unlocked;
+}
+
+/*
+ * Generally, VFIO needs to unpin remote pages after each IOTLB flush.
+ * Therefore, when using IOTLB flush sync interface, VFIO need to keep track
+ * of these regions (currently using a list).
+ *
+ * This value specifies maximum number of regions for each IOTLB flush sync.
+ */
+#define VFIO_IOMMU_TLB_SYNC_MAX		512
+
+static size_t unmap_unpin_fast(struct vfio_domain *domain,
+			       struct vfio_dma *dma, dma_addr_t *iova,
+			       size_t len, phys_addr_t phys, long *unlocked,
+			       struct list_head *unmapped_list,
+			       int *unmapped_cnt)
+{
+	size_t unmapped = 0;
+	struct vfio_regions *entry = kzalloc(sizeof(*entry), GFP_KERNEL);
+
+	if (entry) {
+		unmapped = iommu_unmap_fast(domain->domain, *iova, len);
+
+		if (!unmapped) {
+			kfree(entry);
+		} else {
+			iommu_tlb_range_add(domain->domain, *iova, unmapped);
+			entry->iova = *iova;
+			entry->phys = phys;
+			entry->len  = unmapped;
+			list_add_tail(&entry->list, unmapped_list);
+
+			*iova += unmapped;
+			(*unmapped_cnt)++;
+		}
+	}
+
+	/*
+	 * Sync if the number of fast-unmap regions hits the limit
+	 * or in case of errors.
+	 */
+	if (*unmapped_cnt >= VFIO_IOMMU_TLB_SYNC_MAX || !unmapped) {
+		*unlocked += vfio_sync_unpin(dma, domain,
+					     unmapped_list);
+		*unmapped_cnt = 0;
+	}
+
+	return unmapped;
+}
+
+static size_t unmap_unpin_slow(struct vfio_domain *domain,
+			       struct vfio_dma *dma, dma_addr_t *iova,
+			       size_t len, phys_addr_t phys,
+			       long *unlocked)
+{
+	size_t unmapped = iommu_unmap(domain->domain, *iova, len);
+
+	if (unmapped) {
+		*unlocked += vfio_unpin_pages_remote(dma, *iova,
+						     phys >> PAGE_SHIFT,
+						     unmapped >> PAGE_SHIFT,
+						     false);
+		*iova += unmapped;
+		cond_resched();
+	}
+	return unmapped;
+}
+
 static long vfio_unmap_unpin(struct vfio_iommu *iommu, struct vfio_dma *dma,
 			     bool do_accounting)
 {
 	dma_addr_t iova = dma->iova, end = dma->iova + dma->size;
 	struct vfio_domain *domain, *d;
+	LIST_HEAD(unmapped_region_list);
+	int unmapped_region_cnt = 0;
 	long unlocked = 0;
 
 	if (!dma->size)
@@ -710,20 +813,26 @@ static long vfio_unmap_unpin(struct vfio_iommu *iommu, struct vfio_dma *dma,
 				break;
 		}
 
-		unmapped = iommu_unmap(domain->domain, iova, len);
-		if (WARN_ON(!unmapped))
-			break;
-
-		unlocked += vfio_unpin_pages_remote(dma, iova,
-						    phys >> PAGE_SHIFT,
-						    unmapped >> PAGE_SHIFT,
-						    false);
-		iova += unmapped;
-
-		cond_resched();
+		/*
+		 * First, try to use fast unmap/unpin. In case of failure,
+		 * switch to slow unmap/unpin path.
+		 */
+		unmapped = unmap_unpin_fast(domain, dma, &iova, len, phys,
+					    &unlocked, &unmapped_region_list,
+					    &unmapped_region_cnt);
+		if (!unmapped) {
+			unmapped = unmap_unpin_slow(domain, dma, &iova, len,
+						    phys, &unlocked);
+			if (WARN_ON(!unmapped))
+				break;
+		}
 	}
 
 	dma->iommu_mapped = false;
+
+	if (unmapped_region_cnt)
+		unlocked += vfio_sync_unpin(dma, domain, &unmapped_region_list);
+
 	if (do_accounting) {
 		vfio_lock_acct(dma->task, -unlocked, NULL);
 		return 0;
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 -------- */
 
 /**
diff --git a/samples/vfio-mdev/mtty.c b/samples/vfio-mdev/mtty.c
index 09f255bdf3ac..7abb79d8313d 100644
--- a/samples/vfio-mdev/mtty.c
+++ b/samples/vfio-mdev/mtty.c
@@ -534,7 +534,7 @@ static void handle_bar_read(unsigned int index, struct mdev_state *mdev_state,
 
 		/* Interrupt priority 2: Fifo trigger level reached */
 		if ((ier & UART_IER_RDI) &&
-		    (mdev_state->s[index].rxtx.count ==
+		    (mdev_state->s[index].rxtx.count >=
 		      mdev_state->s[index].intr_trigger_level))
 			*buf |= UART_IIR_RDI;