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    Subject[PATCH v7 3/5] vfio/pci: Mask INTx during runtime suspend
    Date
    This patch adds INTx handling during runtime suspend/resume.
    All the suspend/resume related code for the user to put the device
    into the low power state will be added in subsequent patches.

    The INTx lines may be shared among devices. Whenever any INTx
    interrupt comes for the VFIO devices, then vfio_intx_handler() will be
    called for each device sharing the interrupt. Inside vfio_intx_handler(),
    it calls pci_check_and_mask_intx() and checks if the interrupt has
    been generated for the current device. Now, if the device is already
    in the D3cold state, then the config space can not be read. Attempt
    to read config space in D3cold state can cause system unresponsiveness
    in a few systems. To prevent this, mask INTx in runtime suspend callback,
    and unmask the same in runtime resume callback. If INTx has been already
    masked, then no handling is needed in runtime suspend/resume callbacks.
    'pm_intx_masked' tracks this, and vfio_pci_intx_mask() has been updated
    to return true if the INTx vfio_pci_irq_ctx.masked value is changed
    inside this function.

    For the runtime suspend which is triggered for the no user of VFIO
    device, the 'irq_type' will be VFIO_PCI_NUM_IRQS and these
    callbacks won't do anything.

    The MSI/MSI-X are not shared so similar handling should not be
    needed for MSI/MSI-X. vfio_msihandler() triggers eventfd_signal()
    without doing any device-specific config access. When the user performs
    any config access or IOCTL after receiving the eventfd notification,
    then the device will be moved to the D0 state first before
    servicing any request.

    Another option was to check this flag 'pm_intx_masked' inside
    vfio_intx_handler() instead of masking the interrupts. This flag
    is being set inside the runtime_suspend callback but the device
    can be in non-D3cold state (for example, if the user has disabled D3cold
    explicitly by sysfs, the D3cold is not supported in the platform, etc.).
    Also, in D3cold supported case, the device will be in D0 till the
    PCI core moves the device into D3cold. In this case, there is
    a possibility that the device can generate an interrupt. Adding check
    in the IRQ handler will not clear the IRQ status and the interrupt
    line will still be asserted. This can cause interrupt flooding.

    Signed-off-by: Abhishek Sahu <abhsahu@nvidia.com>
    ---
    drivers/vfio/pci/vfio_pci_core.c | 38 +++++++++++++++++++++++++++----
    drivers/vfio/pci/vfio_pci_intrs.c | 6 ++++-
    drivers/vfio/pci/vfio_pci_priv.h | 2 +-
    include/linux/vfio_pci_core.h | 1 +
    4 files changed, 41 insertions(+), 6 deletions(-)

    diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c
    index 9273f1ffd0dd..207ede189c2a 100644
    --- a/drivers/vfio/pci/vfio_pci_core.c
    +++ b/drivers/vfio/pci/vfio_pci_core.c
    @@ -277,16 +277,46 @@ int vfio_pci_set_power_state(struct vfio_pci_core_device *vdev, pci_power_t stat
    return ret;
    }

    +#ifdef CONFIG_PM
    +static int vfio_pci_core_runtime_suspend(struct device *dev)
    +{
    + struct vfio_pci_core_device *vdev = dev_get_drvdata(dev);
    +
    + /*
    + * If INTx is enabled, then mask INTx before going into the runtime
    + * suspended state and unmask the same in the runtime resume.
    + * If INTx has already been masked by the user, then
    + * vfio_pci_intx_mask() will return false and in that case, INTx
    + * should not be unmasked in the runtime resume.
    + */
    + vdev->pm_intx_masked = ((vdev->irq_type == VFIO_PCI_INTX_IRQ_INDEX) &&
    + vfio_pci_intx_mask(vdev));
    +
    + return 0;
    +}
    +
    +static int vfio_pci_core_runtime_resume(struct device *dev)
    +{
    + struct vfio_pci_core_device *vdev = dev_get_drvdata(dev);
    +
    + if (vdev->pm_intx_masked)
    + vfio_pci_intx_unmask(vdev);
    +
    + return 0;
    +}
    +#endif /* CONFIG_PM */
    +
    /*
    - * The dev_pm_ops needs to be provided to make pci-driver runtime PM working,
    - * so use structure without any callbacks.
    - *
    * The pci-driver core runtime PM routines always save the device state
    * before going into suspended state. If the device is going into low power
    * state with only with runtime PM ops, then no explicit handling is needed
    * for the devices which have NoSoftRst-.
    */
    -static const struct dev_pm_ops vfio_pci_core_pm_ops = { };
    +static const struct dev_pm_ops vfio_pci_core_pm_ops = {
    + SET_RUNTIME_PM_OPS(vfio_pci_core_runtime_suspend,
    + vfio_pci_core_runtime_resume,
    + NULL)
    +};

    int vfio_pci_core_enable(struct vfio_pci_core_device *vdev)
    {
    diff --git a/drivers/vfio/pci/vfio_pci_intrs.c b/drivers/vfio/pci/vfio_pci_intrs.c
    index 8cb987ef3c47..40c3d7cf163f 100644
    --- a/drivers/vfio/pci/vfio_pci_intrs.c
    +++ b/drivers/vfio/pci/vfio_pci_intrs.c
    @@ -59,10 +59,12 @@ static void vfio_send_intx_eventfd(void *opaque, void *unused)
    eventfd_signal(vdev->ctx[0].trigger, 1);
    }

    -void vfio_pci_intx_mask(struct vfio_pci_core_device *vdev)
    +/* Returns true if the INTx vfio_pci_irq_ctx.masked value is changed. */
    +bool vfio_pci_intx_mask(struct vfio_pci_core_device *vdev)
    {
    struct pci_dev *pdev = vdev->pdev;
    unsigned long flags;
    + bool masked_changed = false;

    spin_lock_irqsave(&vdev->irqlock, flags);

    @@ -86,9 +88,11 @@ void vfio_pci_intx_mask(struct vfio_pci_core_device *vdev)
    disable_irq_nosync(pdev->irq);

    vdev->ctx[0].masked = true;
    + masked_changed = true;
    }

    spin_unlock_irqrestore(&vdev->irqlock, flags);
    + return masked_changed;
    }

    /*
    diff --git a/drivers/vfio/pci/vfio_pci_priv.h b/drivers/vfio/pci/vfio_pci_priv.h
    index 58b8d34c162c..5e4fa69aee16 100644
    --- a/drivers/vfio/pci/vfio_pci_priv.h
    +++ b/drivers/vfio/pci/vfio_pci_priv.h
    @@ -23,7 +23,7 @@ struct vfio_pci_ioeventfd {
    bool test_mem;
    };

    -void vfio_pci_intx_mask(struct vfio_pci_core_device *vdev);
    +bool vfio_pci_intx_mask(struct vfio_pci_core_device *vdev);
    void vfio_pci_intx_unmask(struct vfio_pci_core_device *vdev);

    int vfio_pci_set_irqs_ioctl(struct vfio_pci_core_device *vdev, uint32_t flags,
    diff --git a/include/linux/vfio_pci_core.h b/include/linux/vfio_pci_core.h
    index e5cf0d3313a6..a0f1f36e42a2 100644
    --- a/include/linux/vfio_pci_core.h
    +++ b/include/linux/vfio_pci_core.h
    @@ -78,6 +78,7 @@ struct vfio_pci_core_device {
    bool needs_reset;
    bool nointx;
    bool needs_pm_restore;
    + bool pm_intx_masked;
    struct pci_saved_state *pci_saved_state;
    struct pci_saved_state *pm_save;
    int ioeventfds_nr;
    --
    2.17.1
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