Patch "vfio/pci: Implement ioeventfd thread handler for contended memory lock" has been added to the 5.9-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    vfio/pci: Implement ioeventfd thread handler for contended memory lock

to the 5.9-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     vfio-pci-implement-ioeventfd-thread-handler-for-cont.patch
and it can be found in the queue-5.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit ef3bbb2d3a2ef48c5d4280b619a63bf796d613f7
Author: Alex Williamson <alex.williamson@xxxxxxxxxx>
Date:   Mon Nov 2 15:02:00 2020 -0700

    vfio/pci: Implement ioeventfd thread handler for contended memory lock
    
    [ Upstream commit 38565c93c8a1306dc5f245572a545fbea908ac41 ]
    
    The ioeventfd is called under spinlock with interrupts disabled,
    therefore if the memory lock is contended defer code that might
    sleep to a thread context.
    
    Fixes: bc93b9ae0151 ("vfio-pci: Avoid recursive read-lock usage")
    Link: https://bugzilla.kernel.org/show_bug.cgi?id=209253#c1
    Reported-by: Ian Pilcher <arequipeno@xxxxxxxxx>
    Tested-by: Ian Pilcher <arequipeno@xxxxxxxxx>
    Tested-by: Justin Gatzen <justin.gatzen@xxxxxxxxx>
    Signed-off-by: Alex Williamson <alex.williamson@xxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/drivers/vfio/pci/vfio_pci_rdwr.c b/drivers/vfio/pci/vfio_pci_rdwr.c
index 9e353c484ace2..a0b5fc8e46f4d 100644
--- a/drivers/vfio/pci/vfio_pci_rdwr.c
+++ b/drivers/vfio/pci/vfio_pci_rdwr.c
@@ -356,34 +356,60 @@ 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)
+static void vfio_pci_ioeventfd_do_write(struct vfio_pci_ioeventfd *ioeventfd,
+					bool test_mem)
 {
-	struct vfio_pci_ioeventfd *ioeventfd = opaque;
-
 	switch (ioeventfd->count) {
 	case 1:
-		vfio_pci_iowrite8(ioeventfd->vdev, ioeventfd->test_mem,
+		vfio_pci_iowrite8(ioeventfd->vdev, test_mem,
 				  ioeventfd->data, ioeventfd->addr);
 		break;
 	case 2:
-		vfio_pci_iowrite16(ioeventfd->vdev, ioeventfd->test_mem,
+		vfio_pci_iowrite16(ioeventfd->vdev, test_mem,
 				   ioeventfd->data, ioeventfd->addr);
 		break;
 	case 4:
-		vfio_pci_iowrite32(ioeventfd->vdev, ioeventfd->test_mem,
+		vfio_pci_iowrite32(ioeventfd->vdev, test_mem,
 				   ioeventfd->data, ioeventfd->addr);
 		break;
 #ifdef iowrite64
 	case 8:
-		vfio_pci_iowrite64(ioeventfd->vdev, ioeventfd->test_mem,
+		vfio_pci_iowrite64(ioeventfd->vdev, test_mem,
 				   ioeventfd->data, ioeventfd->addr);
 		break;
 #endif
 	}
+}
+
+static int vfio_pci_ioeventfd_handler(void *opaque, void *unused)
+{
+	struct vfio_pci_ioeventfd *ioeventfd = opaque;
+	struct vfio_pci_device *vdev = ioeventfd->vdev;
+
+	if (ioeventfd->test_mem) {
+		if (!down_read_trylock(&vdev->memory_lock))
+			return 1; /* Lock contended, use thread */
+		if (!__vfio_pci_memory_enabled(vdev)) {
+			up_read(&vdev->memory_lock);
+			return 0;
+		}
+	}
+
+	vfio_pci_ioeventfd_do_write(ioeventfd, false);
+
+	if (ioeventfd->test_mem)
+		up_read(&vdev->memory_lock);
 
 	return 0;
 }
 
+static void vfio_pci_ioeventfd_thread(void *opaque, void *unused)
+{
+	struct vfio_pci_ioeventfd *ioeventfd = opaque;
+
+	vfio_pci_ioeventfd_do_write(ioeventfd, ioeventfd->test_mem);
+}
+
 long vfio_pci_ioeventfd(struct vfio_pci_device *vdev, loff_t offset,
 			uint64_t data, int count, int fd)
 {
@@ -457,7 +483,8 @@ long vfio_pci_ioeventfd(struct vfio_pci_device *vdev, loff_t offset,
 	ioeventfd->test_mem = vdev->pdev->resource[bar].flags & IORESOURCE_MEM;
 
 	ret = vfio_virqfd_enable(ioeventfd, vfio_pci_ioeventfd_handler,
-				 NULL, NULL, &ioeventfd->virqfd, fd);
+				 vfio_pci_ioeventfd_thread, NULL,
+				 &ioeventfd->virqfd, fd);
 	if (ret) {
 		kfree(ioeventfd);
 		goto out_unlock;