cc2742fe36
Currently, if the runtime power management is enabled for vfio-pci based devices in the guest OS, then the guest OS will do the register write for PCI_PM_CTRL register. This write request will be handled in vfio_pm_config_write() where it will do the actual register write of PCI_PM_CTRL register. With this, the maximum D3hot state can be achieved for low power. If we can use the runtime PM framework, then we can achieve the D3cold state (on the supported systems) which will help in saving maximum power. 1. D3cold state can't be achieved by writing PCI standard PM config registers. This patch implements the following newly added low power related device features: - VFIO_DEVICE_FEATURE_LOW_POWER_ENTRY - VFIO_DEVICE_FEATURE_LOW_POWER_EXIT The VFIO_DEVICE_FEATURE_LOW_POWER_ENTRY feature will allow the device to make use of low power platform states on the host while the VFIO_DEVICE_FEATURE_LOW_POWER_EXIT will prevent further use of those power states. 2. The vfio-pci driver uses runtime PM framework for low power entry and exit. On the platforms where D3cold state is supported, the runtime PM framework will put the device into D3cold otherwise, D3hot or some other power state will be used. There are various cases where the device will not go into the runtime suspended state. For example, - The runtime power management is disabled on the host side for the device. - The user keeps the device busy after calling LOW_POWER_ENTRY. - There are dependent devices that are still in runtime active state. For these cases, the device will be in the same power state that has been configured by the user through PCI_PM_CTRL register. 3. The hypervisors can implement virtual ACPI methods. For example, in guest linux OS if PCI device ACPI node has _PR3 and _PR0 power resources with _ON/_OFF method, then guest linux OS invokes the _OFF method during D3cold transition and then _ON during D0 transition. The hypervisor can tap these virtual ACPI calls and then call the low power device feature IOCTL. 4. The 'pm_runtime_engaged' flag tracks the entry and exit to runtime PM. This flag is protected with 'memory_lock' semaphore. 5. All the config and other region access are wrapped under pm_runtime_resume_and_get() and pm_runtime_put(). So, if any device access happens while the device is in the runtime suspended state, then the device will be resumed first before access. Once the access has been finished, then the device will again go into the runtime suspended state. 6. The memory region access through mmap will not be allowed in the low power state. Since __vfio_pci_memory_enabled() is a common function, so check for 'pm_runtime_engaged' has been added explicitly in vfio_pci_mmap_fault() to block only mmap'ed access. Signed-off-by: Abhishek Sahu <abhsahu@nvidia.com> Link: https://lore.kernel.org/r/20220829114850.4341-5-abhsahu@nvidia.com Signed-off-by: Alex Williamson <alex.williamson@redhat.com> |
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.. | ||
fsl-mc | ||
mdev | ||
pci | ||
platform | ||
Kconfig | ||
Makefile | ||
vfio_iommu_spapr_tce.c | ||
vfio_iommu_type1.c | ||
vfio_main.c | ||
vfio_spapr_eeh.c | ||
vfio.h | ||
virqfd.c |