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;