Re: [PATCH v13] PCI/ASPM: Make pci_save_aspm_l1ss_state save both child and parent's L1SS configuration

[Bjorn Helgaas <helgaas@kernel.org>]

[+to Alex, +cc kvm]

On Fri, Nov 15, 2024 at 03:22:02PM +0800, Jian-Hong Pan wrote:
> PCI devices' parameters on the VMD bus have been programmed properly
> originally. But, cleared after pci_reset_bus() and have not been restored
> correctly. This leads the link's L1.2 between PCIe Root Port and child
> device gets wrong configs.

17423360a27a ("PCI/ASPM: Save L1 PM Substates Capability for
suspend/resume") appeared in v6.9 and added a bug in the save/restore
path: we save the device L1SS state, but restore both the device L1SS
state and the parent's L1SS state (when the parent state may be junk)
afterwards.

Jian-Hong sees this on VMD, which makes sense because vmd uses
pci_reset_bus() when enabling the VMD domain.

But this should be a problem for any device reset, so I added you,
Alex, in case you've seen this with the resets VFIO does?

We also save/restore for suspend, but I suppose we don't notice the
problem there because in that case we save state for *all* devices,
so the parent state should be valid when we restore.

> Here is a failed example on ASUS B1400CEAE with enabled VMD. Both PCIe
> bridge and NVMe device should have the same LTR1.2_Threshold value.
> However, they are configured as different values in this case:
> 
> 10000:e0:06.0 PCI bridge [0604]: Intel Corporation 11th Gen Core Processor PCIe Controller [8086:9a09] (rev 01) (prog-if 00 [Normal decode])
>   ...
>   Capabilities: [200 v1] L1 PM Substates
>     L1SubCtl1: PCI-PM_L1.2- PCI-PM_L1.1- ASPM_L1.2+ ASPM_L1.1-
>       T_CommonMode=0us LTR1.2_Threshold=0ns
>     L1SubCtl2: T_PwrOn=0us
> 
> 10000:e1:00.0 Non-Volatile memory controller [0108]: Sandisk Corp WD Blue SN550 NVMe SSD [15b7:5009] (rev 01) (prog-if 02 [NVM Express])
>   ...
>   Capabilities: [900 v1] L1 PM Substates
>     L1SubCtl1: PCI-PM_L1.2- PCI-PM_L1.1- ASPM_L1.2+ ASPM_L1.1-
>       T_CommonMode=0us LTR1.2_Threshold=101376ns
>     L1SubCtl2: T_PwrOn=50us

I think T_PwrOn should also be the same for both devices, FWIW.

In fact, I think L1SS should be configured identically for both ends
of the link, with the exceptions of Link Activation and
Common_Mode_Restore_Time, which are RsvdP for the Upstream Port.

> Here is VMD mapped PCI device tree:
> 
> -+-[0000:00]-+-00.0  Intel Corporation Device 9a04
>  | ...
>  \-[10000:e0]-+-06.0-[e1]----00.0  Sandisk Corp WD Blue SN550 NVMe SSD
>               \-17.0  Intel Corporation Tiger Lake-LP SATA Controller
> 
> When pci_reset_bus() resets the bus [e1] of the NVMe, it only saves and
> restores NVMe's state before and after reset. Then, when it restores the
> NVMe's state, ASPM code restores L1SS for both the parent bridge and the
> NVMe in pci_restore_aspm_l1ss_state(). The NVMe's L1SS is restored
> correctly. But, the parent bridge's L1SS is restored with a wrong value 0x0
> because the parent bridge's L1SS wasn't saved by pci_save_aspm_l1ss_state()
> before reset.
> 
> To avoid pci_restore_aspm_l1ss_state() restore wrong value to the parent's
> L1SS config like this example, make pci_save_aspm_l1ss_state() save the
> parent's L1SS config, if the PCI device has a parent.
> 
> Link: https://lore.kernel.org/linux-pci/CAPpJ_eexU0gCHMbXw_z924WxXw0+B6SdS4eG9oGpEX1wmnMLkQ@mail.gmail.com/
> Closes: https://bugzilla.kernel.org/show_bug.cgi?id=218394
> Fixes: 17423360a27a ("PCI/ASPM: Save L1 PM Substates Capability for suspend/resume")
> Suggested-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
> Signed-off-by: Jian-Hong Pan <jhp@endlessos.org>
> Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
> Reviewed-by: David E. Box <david.e.box@linux.intel.com>
> ---
> v9:
> - Drop the v8 fix about drivers/pci/pcie/aspm.c. Use this in VMD instead.
> 
> v10:
> - Drop the v9 fix about drivers/pci/controller/vmd.c
> - Fix in PCIe ASPM to make it symmetric between pci_save_aspm_l1ss_state()
>   and pci_restore_aspm_l1ss_state()
> 
> v11:
> - Introduce __pci_save_aspm_l1ss_state as a resusable helper function
>   which is same as the original pci_configure_aspm_l1ss
> - Make pci_save_aspm_l1ss_state invoke __pci_save_aspm_l1ss_state for
>   both child and parent devices
> - Smooth the commit message
> 
> v12:
> - Update the commit message
> 
> v13:
> - Tweak the commit message to make it more like a general fix
> - When pci_alloc_dev() prepares the pci_dev, it sets the pci_dev's bus.
>   So, let pci_save_aspm_l1ss_state() access pdev's bus directly.
> - Add comment in pci_save_aspm_l1ss_state() to describe why it does not
>   save both the PCIe device and the parent's L1SS config like
>   pci_restore_aspm_l1ss_state() directly.
> 
>  drivers/pci/pcie/aspm.c | 18 +++++++++++++++++-
>  1 file changed, 17 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/pci/pcie/aspm.c b/drivers/pci/pcie/aspm.c
> index 28567d457613..0bcd060aab32 100644
> --- a/drivers/pci/pcie/aspm.c
> +++ b/drivers/pci/pcie/aspm.c
> @@ -79,7 +79,7 @@ void pci_configure_aspm_l1ss(struct pci_dev *pdev)
>  			ERR_PTR(rc));
>  }
>  
> -void pci_save_aspm_l1ss_state(struct pci_dev *pdev)
> +static void __pci_save_aspm_l1ss_state(struct pci_dev *pdev)
>  {
>  	struct pci_cap_saved_state *save_state;
>  	u16 l1ss = pdev->l1ss;
> @@ -101,6 +101,22 @@ void pci_save_aspm_l1ss_state(struct pci_dev *pdev)
>  	pci_read_config_dword(pdev, l1ss + PCI_L1SS_CTL1, cap++);
>  }
>  
> +void pci_save_aspm_l1ss_state(struct pci_dev *pdev)
> +{
> +	struct pci_dev *parent = pdev->bus->self;
> +
> +	__pci_save_aspm_l1ss_state(pdev);
> +
> +	/*
> +	 * Save parent's L1 substate configuration, if the parent has not saved
> +	 * state. It avoids pci_restore_aspm_l1ss_state() restore wrong value to
> +	 * parent's L1 substate configuration. However, the parent might be
> +	 * nothing, if pdev is a PCI bridge.
> +	 */
> +	if (parent && !parent->state_saved)
> +		__pci_save_aspm_l1ss_state(parent);
> +}
> +
>  void pci_restore_aspm_l1ss_state(struct pci_dev *pdev)
>  {
>  	struct pci_cap_saved_state *pl_save_state, *cl_save_state;
> -- 
> 2.47.0
>