Commit 66d1c4c1 authored by Maxime Coquelin's avatar Maxime Coquelin Committed by Stefan Hajnoczi
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virtio-pci: Fix cross-version migration with older machines 



This patch fixes a cross-version migration regression introduced
by commit d1b4259f ("virtio-bus: Plug devices after features are
negotiated").

The problem is encountered when host's vhost backend does not support
VIRTIO_F_VERSION_1, and migration is initiated from a v2.7 or prior
machine with virtio-pci modern capabilities enabled to a v2.8 machine.

In this case, modern capabilities get exposed to the guest by the source,
whereas the target will detect version 1 is not supported so will only
expose legacy capabilities.

The problem is fixed by introducing a new "x-ignore-backend-features"
property, which is set in v2.7 and prior compatibility modes. Doing this,
v2.7 machine keeps its broken behaviour (enabling modern while version
is not supported), and newer machines will behave correctly.

Reported-by: default avatarMichael Roth <mdroth@linux.vnet.ibm.com>
Reviewed-by: default avatarMarcel Apfelbaum <marcel@redhat.com>
Reviewed-by: default avatarStefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: default avatarMichael S. Tsirkin <mst@redhat.com>
Tested-by: default avatarMichael Roth <mdroth@linux.vnet.ibm.com>
Signed-off-by: default avatarMaxime Coquelin <maxime.coquelin@redhat.com>
Message-id: 20161214163035.3297-1-maxime.coquelin@redhat.com
Suggested-by: default avatarStefan Hajnoczi <stefanha@redhat.com>
Cc: Michael S. Tsirkin <mst@redhat.com>
Cc: Cornelia Huck <cornelia.huck@de.ibm.com>
Cc: Dr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: default avatarMarcel Apfelbaum <marcel@redhat.com>
Reviewed-by: default avatarStefan Hajnoczi <stefanha@redhat.com>
Tested-by: default avatarMichael Roth <mdroth@linux.vnet.ibm.com>
Signed-off-by: default avatarMaxime Coquelin <maxime.coquelin@redhat.com>
Signed-off-by: default avatarStefan Hajnoczi <stefanha@redhat.com>
parent d70678a5

hw/virtio/virtio-pci.c

+4 −1
Original line number Diff line number Diff line
@@ -1580,7 +1580,8 @@ static void virtio_pci_device_plugged(DeviceState *d, Error **errp) 
     * Virtio capabilities present without

     * VIRTIO_F_VERSION_1 confuses guests

     */

    if (!virtio_has_feature(vdev->host_features, VIRTIO_F_VERSION_1)) {

    if (!proxy->ignore_backend_features &&

            !virtio_has_feature(vdev->host_features, VIRTIO_F_VERSION_1)) {

        virtio_pci_disable_modern(proxy);



        if (!legacy) {
@@ -1852,6 +1853,8 @@ static Property virtio_pci_properties[] = { 
                    VIRTIO_PCI_FLAG_DISABLE_PCIE_BIT, false),

    DEFINE_PROP_BIT("page-per-vq", VirtIOPCIProxy, flags,

                    VIRTIO_PCI_FLAG_PAGE_PER_VQ_BIT, false),

    DEFINE_PROP_BOOL("x-ignore-backend-features", VirtIOPCIProxy,

                     ignore_backend_features, false),

    DEFINE_PROP_END_OF_LIST(),

};

hw/virtio/virtio-pci.h

+1 −0
Original line number Diff line number Diff line
@@ -153,6 +153,7 @@ struct VirtIOPCIProxy { 
    int config_cap;

    uint32_t flags;

    bool disable_modern;

    bool ignore_backend_features;

    OnOffAuto disable_legacy;

    uint32_t class_code;

    uint32_t nvectors;

include/hw/compat.h

+4 −0
Original line number Diff line number Diff line
@@ -18,6 +18,10 @@ 
        .driver   = "intel-iommu",\

        .property = "x-buggy-eim",\

        .value    = "true",\

    },{\

        .driver   = "virtio-pci",\

        .property = "x-ignore-backend-features",\

        .value    = "on",\

    },



#define HW_COMPAT_2_6 \