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Re: [Qemu-devel] [PATCH v3] virtio-pci: Fix cross-version migration with
From: |
Stefan Hajnoczi |
Subject: |
Re: [Qemu-devel] [PATCH v3] virtio-pci: Fix cross-version migration with older machines |
Date: |
Wed, 14 Dec 2016 17:18:38 +0000 |
On Wed, Dec 14, 2016 at 4:30 PM, Maxime Coquelin
<address@hidden> wrote:
> 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: Michael Roth <address@hidden>
> Suggested-by: Stefan Hajnoczi <address@hidden>
> Cc: Michael S. Tsirkin <address@hidden>
> Cc: Cornelia Huck <address@hidden>
> Cc: Dr. David Alan Gilbert <address@hidden>
> Reviewed-by: Marcel Apfelbaum <address@hidden>
> Reviewed-by: Stefan Hajnoczi <address@hidden>
> Tested-by: Michael Roth <address@hidden>
> Signed-off-by: Maxime Coquelin <address@hidden>
> ---
>
> V3 fixes commit message with the new property name.
> V2 changes the naming as proposed by Michael T.and Cornelia, and
> fixes commit message.
>
> hw/virtio/virtio-pci.c | 5 ++++-
> hw/virtio/virtio-pci.h | 1 +
> include/hw/compat.h | 4 ++++
> 3 files changed, 9 insertions(+), 1 deletion(-)
>
> diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c
> index 521ba0b..21c2b9d 100644
> --- a/hw/virtio/virtio-pci.c
> +++ b/hw/virtio/virtio-pci.c
> @@ -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(),
> };
>
> diff --git a/hw/virtio/virtio-pci.h b/hw/virtio/virtio-pci.h
> index b2a996f..5e07886 100644
> --- a/hw/virtio/virtio-pci.h
> +++ b/hw/virtio/virtio-pci.h
> @@ -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;
> diff --git a/include/hw/compat.h b/include/hw/compat.h
> index 0f06e11..8dfc7a3 100644
> --- a/include/hw/compat.h
> +++ b/include/hw/compat.h
> @@ -18,6 +18,10 @@
> .driver = "intel-iommu",\
> .property = "x-buggy-eim",\
> .value = "true",\
> + },{\
> + .driver = "virtio-pci",\
> + .property = "x-ignore-backend-features",\
> + .value = "on",\
> },
Waiting for Michael Tsirkin's R-b before applying.
Reviewed-by: Stefan Hajnoczi <address@hidden>