| Message ID | 20220517100219.15146-3-abhsahu@nvidia.com (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | vfio/pci: power management changes | expand |
On Tue, 17 May 2022 15:32:17 +0530 Abhishek Sahu <abhsahu@nvidia.com> wrote: > According to [PCIe v5 9.6.2] for PF Device Power Management States > > "The PF's power management state (D-state) has global impact on its > associated VFs. If a VF does not implement the Power Management > Capability, then it behaves as if it is in an equivalent > power state of its associated PF. > > If a VF implements the Power Management Capability, the Device behavior > is undefined if the PF is placed in a lower power state than the VF. > Software should avoid this situation by placing all VFs in lower power > state before lowering their associated PF's power state." > > From the vfio driver side, user can enable SR-IOV when the PF is in D3hot > state. If VF does not implement the Power Management Capability, then > the VF will be actually in D3hot state and then the VF BAR access will > fail. If VF implements the Power Management Capability, then VF will > assume that its current power state is D0 when the PF is D3hot and > in this case, the behavior is undefined. > > To support PF power management, we need to create power management > dependency between PF and its VF's. The runtime power management support > may help with this where power management dependencies are supported > through device links. But till we have such support in place, we can > disallow the PF to go into low power state, if PF has VF enabled. > There can be a case, where user first enables the VF's and then > disables the VF's. If there is no user of PF, then the PF can put into > D3hot state again. But with this patch, the PF will still be in D0 > state after disabling VF's since detecting this case inside > vfio_pci_core_sriov_configure() requires access to > struct vfio_device::open_count along with its locks. But the subsequent > patches related to runtime PM will handle this case since runtime PM > maintains its own usage count. > > Also, vfio_pci_core_sriov_configure() can be called at any time > (with and without vfio pci device user), so the power state change > needs to be protected with the required locks. > > Signed-off-by: Abhishek Sahu <abhsahu@nvidia.com> > --- > drivers/vfio/pci/vfio_pci_core.c | 11 +++++++++++ > 1 file changed, 11 insertions(+) > > diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c > index b9f222ca48cf..4fe9a4efc751 100644 > --- a/drivers/vfio/pci/vfio_pci_core.c > +++ b/drivers/vfio/pci/vfio_pci_core.c > @@ -217,6 +217,10 @@ int vfio_pci_set_power_state(struct vfio_pci_core_device *vdev, pci_power_t stat > bool needs_restore = false, needs_save = false; > int ret; > > + /* Prevent changing power state for PFs with VFs enabled */ > + if (pci_num_vf(pdev) && state > PCI_D0) > + return -EBUSY; > + > if (vdev->needs_pm_restore) { > if (pdev->current_state < PCI_D3hot && state >= PCI_D3hot) { > pci_save_state(pdev); > @@ -1960,6 +1964,13 @@ int vfio_pci_core_sriov_configure(struct vfio_pci_core_device *vdev, > } > list_add_tail(&vdev->sriov_pfs_item, &vfio_pci_sriov_pfs); > mutex_unlock(&vfio_pci_sriov_pfs_mutex); > + > + /* > + * 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. > + */ > + vfio_pci_lock_and_set_power_state(vdev, PCI_D0); But we need to hold memory_lock across the next function or else userspace could race a write to the PM register to set D3 before pci_num_vf() can protect us. Thanks, Alex > ret = pci_enable_sriov(pdev, nr_virtfn); > if (ret) > goto out_del;
On 5/17/2022 11:57 PM, Alex Williamson wrote: > On Tue, 17 May 2022 15:32:17 +0530 > Abhishek Sahu <abhsahu@nvidia.com> wrote: > >> According to [PCIe v5 9.6.2] for PF Device Power Management States >> >> "The PF's power management state (D-state) has global impact on its >> associated VFs. If a VF does not implement the Power Management >> Capability, then it behaves as if it is in an equivalent >> power state of its associated PF. >> >> If a VF implements the Power Management Capability, the Device behavior >> is undefined if the PF is placed in a lower power state than the VF. >> Software should avoid this situation by placing all VFs in lower power >> state before lowering their associated PF's power state." >> >> From the vfio driver side, user can enable SR-IOV when the PF is in D3hot >> state. If VF does not implement the Power Management Capability, then >> the VF will be actually in D3hot state and then the VF BAR access will >> fail. If VF implements the Power Management Capability, then VF will >> assume that its current power state is D0 when the PF is D3hot and >> in this case, the behavior is undefined. >> >> To support PF power management, we need to create power management >> dependency between PF and its VF's. The runtime power management support >> may help with this where power management dependencies are supported >> through device links. But till we have such support in place, we can >> disallow the PF to go into low power state, if PF has VF enabled. >> There can be a case, where user first enables the VF's and then >> disables the VF's. If there is no user of PF, then the PF can put into >> D3hot state again. But with this patch, the PF will still be in D0 >> state after disabling VF's since detecting this case inside >> vfio_pci_core_sriov_configure() requires access to >> struct vfio_device::open_count along with its locks. But the subsequent >> patches related to runtime PM will handle this case since runtime PM >> maintains its own usage count. >> >> Also, vfio_pci_core_sriov_configure() can be called at any time >> (with and without vfio pci device user), so the power state change >> needs to be protected with the required locks. >> >> Signed-off-by: Abhishek Sahu <abhsahu@nvidia.com> >> --- >> drivers/vfio/pci/vfio_pci_core.c | 11 +++++++++++ >> 1 file changed, 11 insertions(+) >> >> diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c >> index b9f222ca48cf..4fe9a4efc751 100644 >> --- a/drivers/vfio/pci/vfio_pci_core.c >> +++ b/drivers/vfio/pci/vfio_pci_core.c >> @@ -217,6 +217,10 @@ int vfio_pci_set_power_state(struct vfio_pci_core_device *vdev, pci_power_t stat >> bool needs_restore = false, needs_save = false; >> int ret; >> >> + /* Prevent changing power state for PFs with VFs enabled */ >> + if (pci_num_vf(pdev) && state > PCI_D0) >> + return -EBUSY; >> + >> if (vdev->needs_pm_restore) { >> if (pdev->current_state < PCI_D3hot && state >= PCI_D3hot) { >> pci_save_state(pdev); >> @@ -1960,6 +1964,13 @@ int vfio_pci_core_sriov_configure(struct vfio_pci_core_device *vdev, >> } >> list_add_tail(&vdev->sriov_pfs_item, &vfio_pci_sriov_pfs); >> mutex_unlock(&vfio_pci_sriov_pfs_mutex); >> + >> + /* >> + * 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. >> + */ >> + vfio_pci_lock_and_set_power_state(vdev, PCI_D0); > > But we need to hold memory_lock across the next function or else > userspace could race a write to the PM register to set D3 before > pci_num_vf() can protect us. Thanks, > > Alex > Thanks Alex. Yes. We need to bring pci_enable_sriov() also to protect this race condition. I will update this in my next version. Regards, Abhishek >> ret = pci_enable_sriov(pdev, nr_virtfn); >> if (ret) >> goto out_del; >
diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c index b9f222ca48cf..4fe9a4efc751 100644 --- a/drivers/vfio/pci/vfio_pci_core.c +++ b/drivers/vfio/pci/vfio_pci_core.c @@ -217,6 +217,10 @@ int vfio_pci_set_power_state(struct vfio_pci_core_device *vdev, pci_power_t stat bool needs_restore = false, needs_save = false; int ret; + /* Prevent changing power state for PFs with VFs enabled */ + if (pci_num_vf(pdev) && state > PCI_D0) + return -EBUSY; + if (vdev->needs_pm_restore) { if (pdev->current_state < PCI_D3hot && state >= PCI_D3hot) { pci_save_state(pdev); @@ -1960,6 +1964,13 @@ int vfio_pci_core_sriov_configure(struct vfio_pci_core_device *vdev, } list_add_tail(&vdev->sriov_pfs_item, &vfio_pci_sriov_pfs); mutex_unlock(&vfio_pci_sriov_pfs_mutex); + + /* + * 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. + */ + vfio_pci_lock_and_set_power_state(vdev, PCI_D0); ret = pci_enable_sriov(pdev, nr_virtfn); if (ret) goto out_del;
According to [PCIe v5 9.6.2] for PF Device Power Management States "The PF's power management state (D-state) has global impact on its associated VFs. If a VF does not implement the Power Management Capability, then it behaves as if it is in an equivalent power state of its associated PF. If a VF implements the Power Management Capability, the Device behavior is undefined if the PF is placed in a lower power state than the VF. Software should avoid this situation by placing all VFs in lower power state before lowering their associated PF's power state." From the vfio driver side, user can enable SR-IOV when the PF is in D3hot state. If VF does not implement the Power Management Capability, then the VF will be actually in D3hot state and then the VF BAR access will fail. If VF implements the Power Management Capability, then VF will assume that its current power state is D0 when the PF is D3hot and in this case, the behavior is undefined. To support PF power management, we need to create power management dependency between PF and its VF's. The runtime power management support may help with this where power management dependencies are supported through device links. But till we have such support in place, we can disallow the PF to go into low power state, if PF has VF enabled. There can be a case, where user first enables the VF's and then disables the VF's. If there is no user of PF, then the PF can put into D3hot state again. But with this patch, the PF will still be in D0 state after disabling VF's since detecting this case inside vfio_pci_core_sriov_configure() requires access to struct vfio_device::open_count along with its locks. But the subsequent patches related to runtime PM will handle this case since runtime PM maintains its own usage count. Also, vfio_pci_core_sriov_configure() can be called at any time (with and without vfio pci device user), so the power state change needs to be protected with the required locks. Signed-off-by: Abhishek Sahu <abhsahu@nvidia.com> --- drivers/vfio/pci/vfio_pci_core.c | 11 +++++++++++ 1 file changed, 11 insertions(+)