[PATCH 5.9 044/255] vfio/pci: Implement ioeventfd thread handler for contended memory lock

Greg Kroah-Hartman
2020-11-17T13:50:53Z

From: Alex Williamson <alex.williamson@redhat.com>

[ 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@gmail.com>
Tested-by: Ian Pilcher <arequipeno@gmail.com>
Tested-by: Justin Gatzen <justin.gatzen@gmail.com>
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/vfio/pci/vfio_pci_rdwr.c | 43 ++++++++++++++++++++++++++------
1 file changed, 35 insertions(+), 8 deletions(-)

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;
--
2.27.0