Commit 38565c93 authored by Alex Williamson's avatar Alex Williamson
Browse files

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

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: bc93b9ae ("vfio-pci: Avoid recursive read-lock usage")
Link: https://bugzilla.kernel.org/show_bug.cgi?id=209253#c1


Reported-by: default avatarIan Pilcher <arequipeno@gmail.com>
Tested-by: default avatarIan Pilcher <arequipeno@gmail.com>
Tested-by: default avatarJustin Gatzen <justin.gatzen@gmail.com>
Signed-off-by: default avatarAlex Williamson <alex.williamson@redhat.com>
parent 8e91cb38

drivers/vfio/pci/vfio_pci_rdwr.c

+35 −8
Original line number Diff line number Diff line
@@ -356,33 +356,59 @@ 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;

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