On 15/03/2019 08:33, Leo Yan wrote:
> Since PCI forbids enabling INTx, MSI or MSIX at the same time, it's by
> default to disable INTx mode when enable MSI/MSIX mode; but this logic is
> easily broken if the guest PCI driver detects the MSI/MSIX cannot work as
> expected and tries to rollback to use INTx mode. The INTx mode has been
> disabled and it has no chance to be enabled again, thus both INTx mode
> and MSI/MSIX mode will not be enabled in vfio for this case.
>
> Below shows the detailed flow for introducing this issue:
>
> vfio_pci_configure_dev_irqs()
> `-> vfio_pci_enable_intx()
>
> vfio_pci_enable_msis()
> `-> vfio_pci_disable_intx()
>
> vfio_pci_disable_msis() => Guest PCI driver disables MSI
>
> To fix this issue, when disable MSI/MSIX we need to check if INTx mode
> is available for this device or not; if the device can support INTx then
> we need to re-enable it so the device can fallback to use it.
>
> Signed-off-by: Leo Yan <leo.yan@xxxxxxxxxx>
> ---
> vfio/pci.c | 17 ++++++++++++-----
> 1 file changed, 12 insertions(+), 5 deletions(-)
>
> diff --git a/vfio/pci.c b/vfio/pci.c
> index c0683f6..44727bb 100644
> --- a/vfio/pci.c
> +++ b/vfio/pci.c
> @@ -28,6 +28,7 @@ struct vfio_irq_eventfd {
> msi_update_state(state, val, VFIO_PCI_MSI_STATE_EMPTY)
>
> static void vfio_pci_disable_intx(struct kvm *kvm, struct vfio_device *vdev);
> +static int vfio_pci_enable_intx(struct kvm *kvm, struct vfio_device *vdev);
>
> static int vfio_pci_enable_msis(struct kvm *kvm, struct vfio_device *vdev,
> bool msix)
> @@ -50,7 +51,7 @@ static int vfio_pci_enable_msis(struct kvm *kvm, struct vfio_device *vdev,
> if (!msi_is_enabled(msis->virt_state))
> return 0;
>
> - if (pdev->irq_modes & VFIO_PCI_IRQ_MODE_INTX) {
> + if (pdev->irq_modes & VFIO_PCI_IRQ_MODE_INTX)
> /*
> * PCI (and VFIO) forbids enabling INTx, MSI or MSIX at the same
> * time. Since INTx has to be enabled from the start (we don't
> @@ -58,9 +59,6 @@ static int vfio_pci_enable_msis(struct kvm *kvm, struct vfio_device *vdev,
> * disable it now.
> */
> vfio_pci_disable_intx(kvm, vdev);
> - /* Permanently disable INTx */
> - pdev->irq_modes &= ~VFIO_PCI_IRQ_MODE_INTX;
As a result vfio_pci_disable_intx() may be called multiple times (each
time the guest enables one MSI vector). Could you make
vfio_pci_disable_intx() safe against that (maybe use intx_fd == -1 to
denote the INTx state)?
> - }
>
> eventfds = (void *)msis->irq_set + sizeof(struct vfio_irq_set);
>
> @@ -162,7 +160,16 @@ static int vfio_pci_disable_msis(struct kvm *kvm, struct vfio_device *vdev,
> msi_set_enabled(msis->phys_state, false);
> msi_set_empty(msis->phys_state, true);
>
> - return 0;
> + if (pdev->irq_modes & VFIO_PCI_IRQ_MODE_INTX)
> + /*
> + * When MSI or MSIX is disabled, this might be called when
> + * PCI driver detects the MSI interrupt failure and wants to
> + * rollback to INTx mode. Thus enable INTx if the device
> + * supports INTx mode in this case.
> + */
> + ret = vfio_pci_enable_intx(kvm, vdev);
Let's remove vfio_pci_reserve_irq_fds(2) from vfio_pci_enable_intx(), it
should only called once per run, and isn't particularly useful here
since INTx only uses 2 fds. It's used to bump the fd rlimit when a
device needs ~2048 file descriptors for MSI-X.
Thanks,
Jean
> +
> + return ret >= 0 ? 0 : ret;
> }
>
> static int vfio_pci_update_msi_entry(struct kvm *kvm, struct vfio_device *vdev,
>
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