Re: [PATCH v3 5/8] vfio/pci: Enable runtime PM for vfio_pci_core based drivers

Alex Williamson
2022-05-04T19:43:05Z

On Mon, 25 Apr 2022 14:56:12 +0530
Abhishek Sahu <abhsahu@nvidia.com> wrote:

> Currently, there is very limited power management support
> available in the upstream vfio_pci_core based drivers. If there
> are no users of the device, then the PCI device will be moved into
> D3hot state by writing directly into PCI PM registers. This D3hot
> state help in saving power but we can achieve zero power consumption
> if we go into the D3cold state. The D3cold state cannot be possible
> with native PCI PM. It requires interaction with platform firmware
> which is system-specific. To go into low power states (including D3cold),
> the runtime PM framework can be used which internally interacts with PCI
> and platform firmware and puts the device into the lowest possible
> D-States.
>
> This patch registers vfio_pci_core based drivers with the
> runtime PM framework.
>
> 1. The PCI core framework takes care of most of the runtime PM
> related things. For enabling the runtime PM, the PCI driver needs to
> decrement the usage count and needs to provide 'struct dev_pm_ops'
> at least. The runtime suspend/resume callbacks are optional and needed
> only if we need to do any extra handling. Now there are multiple
> vfio_pci_core based drivers. Instead of assigning the
> 'struct dev_pm_ops' in individual parent driver, the vfio_pci_core
> itself assigns the 'struct dev_pm_ops'. There are other drivers where
> the 'struct dev_pm_ops' is being assigned inside core layer
> (For example, wlcore_probe() and some sound based driver, etc.).
>
> 2. This patch provides the stub implementation of 'struct dev_pm_ops'.
> The subsequent patch will provide the runtime suspend/resume
> callbacks. All the config state saving, and PCI power management
> related things will be done by PCI core framework itself inside its
> runtime suspend/resume callbacks (pci_pm_runtime_suspend() and
> pci_pm_runtime_resume()).
>
> 3. Inside pci_reset_bus(), all the devices in dev_set needs to be
> runtime resumed. vfio_pci_dev_set_pm_runtime_get() will take
> care of the runtime resume and its error handling.
>
> 4. Inside vfio_pci_core_disable(), the device usage count always needs
> to be decremented which was incremented in vfio_pci_core_enable().
>
> 5. Since the runtime PM framework will provide the same functionality,
> so directly writing into PCI PM config register can be replaced with
> the use of runtime PM routines. Also, the use of runtime PM can help
> us in more power saving.
>
> In the systems which do not support D3cold,
>
> With the existing implementation:
>
> // PCI device
> # cat /sys/bus/pci/devices/0000\:01\:00.0/power_state
> D3hot
> // upstream bridge
> # cat /sys/bus/pci/devices/0000\:00\:01.0/power_state
> D0
>
> With runtime PM:
>
> // PCI device
> # cat /sys/bus/pci/devices/0000\:01\:00.0/power_state
> D3hot
> // upstream bridge
> # cat /sys/bus/pci/devices/0000\:00\:01.0/power_state
> D3hot
>
> So, with runtime PM, the upstream bridge or root port will also go
> into lower power state which is not possible with existing
> implementation.
>
> In the systems which support D3cold,
>
> // PCI device
> # cat /sys/bus/pci/devices/0000\:01\:00.0/power_state
> D3hot
> // upstream bridge
> # cat /sys/bus/pci/devices/0000\:00\:01.0/power_state
> D0
>
> With runtime PM:
>
> // PCI device
> # cat /sys/bus/pci/devices/0000\:01\:00.0/power_state
> D3cold
> // upstream bridge
> # cat /sys/bus/pci/devices/0000\:00\:01.0/power_state
> D3cold
>
> So, with runtime PM, both the PCI device and upstream bridge will
> go into D3cold state.
>
> 6. If 'disable_idle_d3' module parameter is set, then also the runtime
> PM will be enabled, but in this case, the usage count should not be
> decremented.
>
> 7. vfio_pci_dev_set_try_reset() return value is unused now, so this
> function return type can be changed to void.
>
> 8. Use the runtime PM API's in vfio_pci_core_sriov_configure().
> For preventing any runtime usage mismatch, pci_num_vf() has been
> called explicitly during disable.
>
> Signed-off-by: Abhishek Sahu <abhsahu@nvidia.com>
> ---
> drivers/vfio/pci/vfio_pci_core.c | 169 +++++++++++++++++++++----------
> 1 file changed, 114 insertions(+), 55 deletions(-)
>
> diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c
> index 953ac33b2f5f..aee5e0cd6137 100644
> --- a/drivers/vfio/pci/vfio_pci_core.c
> +++ b/drivers/vfio/pci/vfio_pci_core.c
> @@ -156,7 +156,7 @@ static void vfio_pci_probe_mmaps(struct vfio_pci_core_device *vdev)
> }
>
> struct vfio_pci_group_info;
> -static bool vfio_pci_dev_set_try_reset(struct vfio_device_set *dev_set);
> +static void vfio_pci_dev_set_try_reset(struct vfio_device_set *dev_set);
> static int vfio_pci_dev_set_hot_reset(struct vfio_device_set *dev_set,
> struct vfio_pci_group_info *groups);
>
> @@ -261,6 +261,19 @@ int vfio_pci_set_power_state(struct vfio_pci_core_device *vdev, pci_power_t stat
> return ret;
> }
>
> +#ifdef 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 = { };
> +#endif
> +
> int vfio_pci_core_enable(struct vfio_pci_core_device *vdev)
> {
> struct pci_dev *pdev = vdev->pdev;
> @@ -268,21 +281,23 @@ int vfio_pci_core_enable(struct vfio_pci_core_device *vdev)
> u16 cmd;
> u8 msix_pos;
>
> - vfio_pci_set_power_state(vdev, PCI_D0);
> + if (!disable_idle_d3) {
> + ret = pm_runtime_resume_and_get(&pdev->dev);
> + if (ret < 0)
> + return ret;
> + }
>
> /* Don't allow our initial saved state to include busmaster */
> pci_clear_master(pdev);
>
> ret = pci_enable_device(pdev);
> if (ret)
> - return ret;
> + goto out_power;
>
> /* If reset fails because of the device lock, fail this path entirely */
> ret = pci_try_reset_function(pdev);
> - if (ret == -EAGAIN) {
> - pci_disable_device(pdev);
> - return ret;
> - }
> + if (ret == -EAGAIN)
> + goto out_disable_device;
>
> vdev->reset_works = !ret;
> pci_save_state(pdev);
> @@ -306,12 +321,8 @@ int vfio_pci_core_enable(struct vfio_pci_core_device *vdev)
> }
>
> ret = vfio_config_init(vdev);
> - if (ret) {
> - kfree(vdev->pci_saved_state);
> - vdev->pci_saved_state = NULL;
> - pci_disable_device(pdev);
> - return ret;
> - }
> + if (ret)
> + goto out_free_state;
>
> msix_pos = pdev->msix_cap;
> if (msix_pos) {
> @@ -332,6 +343,16 @@ int vfio_pci_core_enable(struct vfio_pci_core_device *vdev)
>
>
> return 0;
> +
> +out_free_state:
> + kfree(vdev->pci_saved_state);
> + vdev->pci_saved_state = NULL;
> +out_disable_device:
> + pci_disable_device(pdev);
> +out_power:
> + if (!disable_idle_d3)
> + pm_runtime_put(&pdev->dev);
> + return ret;
> }
> EXPORT_SYMBOL_GPL(vfio_pci_core_enable);
>
> @@ -439,8 +460,11 @@ void vfio_pci_core_disable(struct vfio_pci_core_device *vdev)
> out:
> pci_disable_device(pdev);
>
> - if (!vfio_pci_dev_set_try_reset(vdev->vdev.dev_set) && !disable_idle_d3)
> - vfio_pci_set_power_state(vdev, PCI_D3hot);
> + vfio_pci_dev_set_try_reset(vdev->vdev.dev_set);
> +
> + /* Put the pm-runtime usage counter acquired during enable */
> + if (!disable_idle_d3)
> + pm_runtime_put(&pdev->dev);
> }
> EXPORT_SYMBOL_GPL(vfio_pci_core_disable);
>
> @@ -1879,19 +1903,24 @@ int vfio_pci_core_register_device(struct vfio_pci_core_device *vdev,
>
> vfio_pci_probe_power_state(vdev);
>
> - if (!disable_idle_d3) {
> - /*
> - * pci-core sets the device power state to an unknown value at
> - * bootup and after being removed from a driver. The only
> - * transition it allows from this unknown state is to D0, which
> - * typically happens when a driver calls pci_enable_device().
> - * We're not ready to enable the device yet, but we do want to
> - * be able to get to D3. Therefore first do a D0 transition
> - * before going to D3.
> - */
> - vfio_pci_set_power_state(vdev, PCI_D0);
> - vfio_pci_set_power_state(vdev, PCI_D3hot);
> - }
> + /*
> + * pci-core sets the device power state to an unknown value at
> + * bootup and after being removed from a driver. The only
> + * transition it allows from this unknown state is to D0, which
> + * typically happens when a driver calls pci_enable_device().
> + * We're not ready to enable the device yet, but we do want to
> + * be able to get to D3. Therefore first do a D0 transition
> + * before enabling runtime PM.
> + */
> + vfio_pci_set_power_state(vdev, PCI_D0);
> +
> +#if defined(CONFIG_PM)
> + dev->driver->pm = &vfio_pci_core_pm_ops,
> +#endif
> +
> + pm_runtime_allow(dev);
> + if (!disable_idle_d3)
> + pm_runtime_put(dev);
>
> ret = vfio_register_group_dev(&vdev->vdev);
> if (ret)
> @@ -1900,7 +1929,9 @@ int vfio_pci_core_register_device(struct vfio_pci_core_device *vdev,
>
> out_power:
> if (!disable_idle_d3)
> - vfio_pci_set_power_state(vdev, PCI_D0);
> + pm_runtime_get_noresume(dev);
> +
> + pm_runtime_forbid(dev);
> out_vf:
> vfio_pci_vf_uninit(vdev);
> out_drvdata:
> @@ -1922,8 +1953,9 @@ void vfio_pci_core_unregister_device(struct vfio_pci_core_device *vdev)
> vfio_pci_vga_uninit(vdev);
>
> if (!disable_idle_d3)
> - vfio_pci_set_power_state(vdev, PCI_D0);
> + pm_runtime_get_noresume(dev);
>
> + pm_runtime_forbid(dev);
> dev_set_drvdata(dev, NULL);
> }
> EXPORT_SYMBOL_GPL(vfio_pci_core_unregister_device);
> @@ -1984,18 +2016,26 @@ int vfio_pci_core_sriov_configure(struct pci_dev *pdev, int nr_virtfn)
>
> /*
> * The PF power state should always be higher than the VF power
> - * state. If PF is in the low power state, then change the
> - * power state to D0 first before enabling SR-IOV.
> + * state. If PF is in the runtime suspended state, then resume
> + * it first before enabling SR-IOV.
> */
> - vfio_pci_set_power_state(vdev, PCI_D0);
> - ret = pci_enable_sriov(pdev, nr_virtfn);
> + ret = pm_runtime_resume_and_get(&pdev->dev);
> if (ret)
> goto out_del;
> +
> + ret = pci_enable_sriov(pdev, nr_virtfn);
> + if (ret) {
> + pm_runtime_put(&pdev->dev);
> + goto out_del;
> + }
> ret = nr_virtfn;
> goto out_put;
> }
>
> - pci_disable_sriov(pdev);
> + if (pci_num_vf(pdev)) {
> + pci_disable_sriov(pdev);
> + pm_runtime_put(&pdev->dev);
> + }
>
> out_del:
> mutex_lock(&vfio_pci_sriov_pfs_mutex);
> @@ -2072,6 +2112,30 @@ vfio_pci_dev_set_resettable(struct vfio_device_set *dev_set)
> return pdev;
> }
>
> +static int vfio_pci_dev_set_pm_runtime_get(struct vfio_device_set *dev_set)
> +{
> + struct vfio_pci_core_device *cur_pm;
> + struct vfio_pci_core_device *cur;
> + int ret = 0;
> +
> + list_for_each_entry(cur_pm, &dev_set->device_list, vdev.dev_set_list) {
> + ret = pm_runtime_resume_and_get(&cur_pm->pdev->dev);
> + if (ret < 0)
> + break;
> + }
> +
> + if (!ret)
> + return 0;
> +
> + list_for_each_entry(cur, &dev_set->device_list, vdev.dev_set_list) {
> + if (cur == cur_pm)
> + break;
> + pm_runtime_put(&cur->pdev->dev);
> + }
> +
> + return ret;
> +}

The above works, but maybe could be a little cleaner taking advantage
of list_for_each_entry_continue_reverse as:

{
struct vfio_pci_core_device *cur;
int ret;

list_for_each_entry(cur, &dev_set->device_list, vdev.dev_set_list) {
ret = pm_runtime_resume_and_get(&cur->pdev->dev);
if (ret)
goto unwind;
}

return 0;

unwind:
list_for_each_entry_continue_reverse(cur, &dev_set->device_list, vdev.dev_set_list)
pm_runtime_put(&cur->pdev->dev);

return ret;
}

Thanks,
Alex

> +
> /*
> * We need to get memory_lock for each device, but devices can share mmap_lock,
> * therefore we need to zap and hold the vma_lock for each device, and only then
> @@ -2178,43 +2242,38 @@ static bool vfio_pci_dev_set_needs_reset(struct vfio_device_set *dev_set)
> * - At least one of the affected devices is marked dirty via
> * needs_reset (such as by lack of FLR support)
> * Then attempt to perform that bus or slot reset.
> - * Returns true if the dev_set was reset.
> */
> -static bool vfio_pci_dev_set_try_reset(struct vfio_device_set *dev_set)
> +static void vfio_pci_dev_set_try_reset(struct vfio_device_set *dev_set)
> {
> struct vfio_pci_core_device *cur;
> struct pci_dev *pdev;
> - int ret;
> + bool reset_done = false;
>
> if (!vfio_pci_dev_set_needs_reset(dev_set))
> - return false;
> + return;
>
> pdev = vfio_pci_dev_set_resettable(dev_set);
> if (!pdev)
> - return false;
> + return;
>
> /*
> - * The pci_reset_bus() will reset all the devices in the bus.
> - * The power state can be non-D0 for some of the devices in the bus.
> - * For these devices, the pci_reset_bus() will internally set
> - * the power state to D0 without vfio driver involvement.
> - * For the devices which have NoSoftRst-, the reset function can
> - * cause the PCI config space reset without restoring the original
> - * state (saved locally in 'vdev->pm_save').
> + * Some of the devices in the bus can be in the runtime suspended
> + * state. Increment the usage count for all the devices in the dev_set
> + * before reset and decrement the same after reset.
> */
> - list_for_each_entry(cur, &dev_set->device_list, vdev.dev_set_list)
> - vfio_pci_set_power_state(cur, PCI_D0);
> + if (!disable_idle_d3 && vfio_pci_dev_set_pm_runtime_get(dev_set))
> + return;
>
> - ret = pci_reset_bus(pdev);
> - if (ret)
> - return false;
> + if (!pci_reset_bus(pdev))
> + reset_done = true;
>
> list_for_each_entry(cur, &dev_set->device_list, vdev.dev_set_list) {
> - cur->needs_reset = false;
> + if (reset_done)
> + cur->needs_reset = false;
> +
> if (!disable_idle_d3)
> - vfio_pci_set_power_state(cur, PCI_D3hot);
> + pm_runtime_put(&cur->pdev->dev);
> }
> - return true;
> }
>
> void vfio_pci_core_set_params(bool is_nointxmask, bool is_disable_vga,