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[Qemu-devel] Re: [PATCH] [Also for STABLE-0.12] Don't check for bus mast
From: |
Michael S. Tsirkin |
Subject: |
[Qemu-devel] Re: [PATCH] [Also for STABLE-0.12] Don't check for bus master for old guests |
Date: |
Tue, 16 Mar 2010 22:21:43 +0200 |
User-agent: |
Mutt/1.5.19 (2009-01-05) |
On Tue, Mar 16, 2010 at 07:18:07PM +0100, Alexander Graf wrote:
> Older Linux guests don't activate the bus master enable bit. So for those we
> can just try to be clever and track if they set the DEVICE_OK bit even though
> bus mastering is still disabled.
>
> Under that condition we can disable the windows safety check. With that logic
> in place both guests should work just fine. Without PCI hotplug breaks
> virtio-net in Linux < 2.6.34 guests.
>
> Signed-off-by: Alexander Graf <address@hidden>
> CC: Michael S. Tsirkin <address@hidden>
> ---
> hw/virtio-pci.c | 25 ++++++++++++++++++++++++-
> 1 files changed, 24 insertions(+), 1 deletions(-)
>
> diff --git a/hw/virtio-pci.c b/hw/virtio-pci.c
> index 3594152..4fc4b3c 100644
> --- a/hw/virtio-pci.c
> +++ b/hw/virtio-pci.c
> @@ -76,6 +76,10 @@
> * 12 is historical, and due to x86 page size. */
> #define VIRTIO_PCI_QUEUE_ADDR_SHIFT 12
>
> +/* We can catch some guest bugs inside here so we continue supporting older
> + guests. */
> +#define VIRTIO_PCI_BUG_BUS_MASTER (1 << 0)
> +
> /* QEMU doesn't strictly need write barriers since everything runs in
> * lock-step. We'll leave the calls to wmb() in though to make it obvious
> for
> * KVM or if kqemu gets SMP support.
> @@ -87,6 +91,7 @@
> typedef struct {
> PCIDevice pci_dev;
> VirtIODevice *vdev;
> + uint32_t bugs;
> uint32_t addr;
> uint32_t class_code;
> uint32_t nvectors;
> @@ -138,6 +143,13 @@ static int virtio_pci_load_config(void * opaque,
> QEMUFile *f)
> if (proxy->vdev->config_vector != VIRTIO_NO_VECTOR) {
> return msix_vector_use(&proxy->pci_dev, proxy->vdev->config_vector);
> }
> +
> + /* Try to find out if the guest has bus master disabled, but is
> + in ready state. Then we have a buggy guest OS. */
> + if (!(proxy->vdev->status & VIRTIO_CONFIG_S_DRIVER_OK) &&
should not this be (proxy->vdev->status & VIRTIO_CONFIG_S_DRIVER_OK)?
> + !(proxy->pci_dev.config[PCI_COMMAND] & PCI_COMMAND_MASTER)) {
> + proxy->bugs |= VIRTIO_PCI_BUG_BUS_MASTER;
> + }
> return 0;
> }
>
> @@ -162,6 +174,7 @@ static void virtio_pci_reset(DeviceState *d)
> VirtIOPCIProxy *proxy = container_of(d, VirtIOPCIProxy, pci_dev.qdev);
> virtio_reset(proxy->vdev);
> msix_reset(&proxy->pci_dev);
> + proxy->bugs = 0;
> }
>
> static void virtio_ioport_write(void *opaque, uint32_t addr, uint32_t val)
> @@ -205,6 +218,14 @@ static void virtio_ioport_write(void *opaque, uint32_t
> addr, uint32_t val)
> virtio_reset(proxy->vdev);
> msix_unuse_all_vectors(&proxy->pci_dev);
> }
> +
> + /* Linux before 2.6.34 sets the device as OK without enabling
> + the PCI device bus master bit. In this case we need to disable
> + some safety checks. */
> + if ((val & VIRTIO_CONFIG_S_DRIVER_OK) &&
> + !(proxy->pci_dev.config[PCI_COMMAND] & PCI_COMMAND_MASTER)) {
> + proxy->bugs |= VIRTIO_PCI_BUG_BUS_MASTER;
> + }
> break;
> case VIRTIO_MSI_CONFIG_VECTOR:
> msix_vector_unuse(&proxy->pci_dev, vdev->config_vector);
> @@ -372,7 +393,9 @@ static void virtio_write_config(PCIDevice *pci_dev,
> uint32_t address,
>
> if (PCI_COMMAND == address) {
> if (!(val & PCI_COMMAND_MASTER)) {
> - proxy->vdev->status &= ~VIRTIO_CONFIG_S_DRIVER_OK;
> + if (!(proxy->bugs & VIRTIO_PCI_BUG_BUS_MASTER)) {
nested if statements are confusing
if (!(val & PCI_COMMAND_MASTER) &&
!(proxy->bugs & VIRTIO_PCI_BUG_BUS_MASTER))
would be clearer.
> + proxy->vdev->status &= ~VIRTIO_CONFIG_S_DRIVER_OK;
> + }
> }
> }
>
> --
> 1.6.0.2