118 lines
5.1 KiB
Diff
118 lines
5.1 KiB
Diff
From 2c8d6826ebaf1bf846edd213f8fe8f95c0c300cb Mon Sep 17 00:00:00 2001
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From: "Michael S. Tsirkin" <mst@redhat.com>
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Date: Thu, 11 Sep 2014 18:34:29 +0300
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Subject: [PATCH] virtio-pci: fix migration for pci bus master
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Current support for bus master (clearing OK bit)
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together with the need to support guests which do not
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enable PCI bus mastering, leads to extra state in
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VIRTIO_PCI_FLAG_BUS_MASTER_BUG bit, which isn't robust
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in case of cross-version migration for the case when
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guests use the device before setting DRIVER_OK.
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Rip out VIRTIO_PCI_FLAG_BUS_MASTER_BUG and implement a simpler
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work-around: treat clearing of PCI_COMMAND as a virtio reset. Old
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guests never touch this bit so they will work.
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As reset clears device status, DRIVER and MASTER bits are
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now in sync, so we can fix up cross-version migration simply
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by synchronising them, without need to detect a buggy guest
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explicitly.
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Drop tracking VIRTIO_PCI_FLAG_BUS_MASTER_BUG completely.
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As reset makes the device quiescent, in the future we'll be able to drop
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checking OK bit in a bunch of places.
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Cc: Jason Wang <jasowang@redhat.com>
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Cc: Greg Kurz <gkurz@linux.vnet.ibm.com>
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Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
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(cherry picked from commit 4d43d3f3c8147ade184df9a1e9e82826edd39e19)
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---
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hw/virtio/virtio-pci.c | 39 ++++++++++++++++++++-------------------
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1 file changed, 20 insertions(+), 19 deletions(-)
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diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c
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index 58ebbcf..c19c4d6 100644
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--- a/hw/virtio/virtio-pci.c
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+++ b/hw/virtio/virtio-pci.c
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@@ -86,9 +86,6 @@
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* 12 is historical, and due to x86 page size. */
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#define VIRTIO_PCI_QUEUE_ADDR_SHIFT 12
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-/* Flags track per-device state like workarounds for quirks in older guests. */
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-#define VIRTIO_PCI_FLAG_BUS_MASTER_BUG (1 << 0)
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-
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static void virtio_pci_bus_new(VirtioBusState *bus, size_t bus_size,
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VirtIOPCIProxy *dev);
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@@ -323,14 +320,6 @@ static void virtio_ioport_write(void *opaque, uint32_t addr, uint32_t val)
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proxy->pci_dev.config[PCI_COMMAND] |
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PCI_COMMAND_MASTER, 1);
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}
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-
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- /* Linux before 2.6.34 sets the device as OK without enabling
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- the PCI device bus master bit. In this case we need to disable
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- some safety checks. */
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- if ((val & VIRTIO_CONFIG_S_DRIVER_OK) &&
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- !(proxy->pci_dev.config[PCI_COMMAND] & PCI_COMMAND_MASTER)) {
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- proxy->flags |= VIRTIO_PCI_FLAG_BUS_MASTER_BUG;
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- }
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break;
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case VIRTIO_MSI_CONFIG_VECTOR:
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msix_vector_unuse(&proxy->pci_dev, vdev->config_vector);
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@@ -480,13 +469,18 @@ static void virtio_write_config(PCIDevice *pci_dev, uint32_t address,
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VirtIOPCIProxy *proxy = DO_UPCAST(VirtIOPCIProxy, pci_dev, pci_dev);
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VirtIODevice *vdev = virtio_bus_get_device(&proxy->bus);
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+ uint8_t cmd = proxy->pci_dev.config[PCI_COMMAND];
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+
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pci_default_write_config(pci_dev, address, val, len);
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if (range_covers_byte(address, len, PCI_COMMAND) &&
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!(pci_dev->config[PCI_COMMAND] & PCI_COMMAND_MASTER) &&
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- !(proxy->flags & VIRTIO_PCI_FLAG_BUS_MASTER_BUG)) {
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+ (cmd & PCI_COMMAND_MASTER)) {
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+ /* Bus driver disables bus mastering - make it act
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+ * as a kind of reset to render the device quiescent. */
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virtio_pci_stop_ioeventfd(proxy);
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- virtio_set_status(vdev, vdev->status & ~VIRTIO_CONFIG_S_DRIVER_OK);
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+ virtio_reset(vdev);
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+ msix_unuse_all_vectors(&proxy->pci_dev);
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}
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}
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@@ -895,11 +889,19 @@ static void virtio_pci_vmstate_change(DeviceState *d, bool running)
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VirtIODevice *vdev = virtio_bus_get_device(&proxy->bus);
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if (running) {
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- /* Try to find out if the guest has bus master disabled, but is
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- in ready state. Then we have a buggy guest OS. */
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- if ((vdev->status & VIRTIO_CONFIG_S_DRIVER_OK) &&
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- !(proxy->pci_dev.config[PCI_COMMAND] & PCI_COMMAND_MASTER)) {
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- proxy->flags |= VIRTIO_PCI_FLAG_BUS_MASTER_BUG;
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+ /* Linux before 2.6.34 drives the device without enabling
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+ the PCI device bus master bit. Enable it automatically
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+ for the guest. This is a PCI spec violation but so is
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+ initiating DMA with bus master bit clear.
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+ Note: this only makes a difference when migrating
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+ across QEMU versions from an old QEMU, as for new QEMU
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+ bus master and driver bits are always in sync.
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+ TODO: consider enabling conditionally for compat machine types. */
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+ if (vdev->status & (VIRTIO_CONFIG_S_ACKNOWLEDGE |
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+ VIRTIO_CONFIG_S_DRIVER)) {
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+ pci_default_write_config(&proxy->pci_dev, PCI_COMMAND,
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+ proxy->pci_dev.config[PCI_COMMAND] |
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+ PCI_COMMAND_MASTER, 1);
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}
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virtio_pci_start_ioeventfd(proxy);
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} else {
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@@ -1043,7 +1045,6 @@ static void virtio_pci_reset(DeviceState *qdev)
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virtio_pci_stop_ioeventfd(proxy);
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virtio_bus_reset(bus);
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msix_unuse_all_vectors(&proxy->pci_dev);
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- proxy->flags &= ~VIRTIO_PCI_FLAG_BUS_MASTER_BUG;
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}
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static Property virtio_pci_properties[] = {
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