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virtio-balloon: fix QEMU 4.0 config size migration incompatibility

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The virtio-balloon config size changed in QEMU 4.0 even for existing
machine types.  Migration from QEMU 3.1 to 4.0 can fail in some
circumstances with the following error:

  qemu-system-x86_64: get_pci_config_device: Bad config data: i=0x10 read: a1 device: 1 cmask: ff wmask: c0 w1cmask:0

This happens because the virtio-balloon config size affects the VIRTIO
Legacy I/O Memory PCI BAR size.

Introduce a qdev property called "qemu-4-0-config-size" and enable it
only for the QEMU 4.0 machine types.  This way <4.0 machine types use
the old size, 4.0 uses the larger size, and >4.0 machine types use the
appropriate size depending on enabled virtio-balloon features.

Live migration to and from old QEMUs to QEMU 4.1 works again as long as
a versioned machine type is specified (do not use just "pc"!).

Originally-by: Wolfgang Bumiller <w.bumiller@proxmox.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-Id: <20190710141440.27635-1-stefanha@redhat.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Tested-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Tested-by: Wolfgang Bumiller <w.bumiller@proxmox.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
This commit is contained in:
Stefan Hajnoczi 2019-07-10 16:14:40 +02:00 • committed by Michael S. Tsirkin
parent 4d90b7a0e4
commit 2bbadb08ce
3 changed files with 29 additions and 3 deletions
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2
hw/core/machine.c
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@ -34,6 +34,7 @@ GlobalProperty hw_compat_4_0[] = {
{ "virtio-vga", "edid", "false" },
{ "virtio-gpu-pci", "edid", "false" },
{ "virtio-device", "use-started", "false" },
{ "virtio-balloon-device", "qemu-4-0-config-size", "true" },
};
const size_t hw_compat_4_0_len = G_N_ELEMENTS(hw_compat_4_0);
@ -49,6 +50,7 @@ GlobalProperty hw_compat_3_1[] = {
{ "usb-tablet", "serial", "42" },
{ "virtio-blk-device", "discard", "false" },
{ "virtio-blk-device", "write-zeroes", "false" },
{ "virtio-balloon-device", "qemu-4-0-config-size", "false" },
};
const size_t hw_compat_3_1_len = G_N_ELEMENTS(hw_compat_3_1);