linux-kernel - Re: [PATCH iwl-net v4] i40e: Restore VF MSI-X state during PCI reset

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Date:   Wed, 13 Dec 2023 13:59:51 -0800
From:   Jacob Keller <jacob.e.keller@...el.com>
To:     Andrii Staikov <andrii.staikov@...el.com>,
        <intel-wired-lan@...ts.osuosl.org>
CC:     <netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        Karen Ostrowska <karen.ostrowska@...el.com>,
        Mateusz Palczewski <mateusz.palczewski@...el.com>,
        Drewek Wojciech <wojciech.drewek@...el.com>,
        Kitszel Przemyslaw <przemyslaw.kitszel@...el.com>
Subject: Re: [PATCH iwl-net v4] i40e: Restore VF MSI-X state during PCI reset



On 12/12/2023 4:24 AM, Andrii Staikov wrote:
> During a PCI FLR the MSI-X Enable flag in the VF PCI MSI-X capability
> register will be cleared. This can lead to issues when a VF is
> assigned to a VM because in these cases the VF driver receives no
> indication of the PF PCI error/reset and additionally it is incapable
> of restoring the cleared flag in the hypervisor configuration space
> without fully reinitializing the driver interrupt functionality.
> 
> Since the VF driver is unable to easily resolve this condition on its own,
> restore the VF MSI-X flag during the PF PCI reset handling.
> 
> Fixes: 19b7960b2da1 ("i40e: implement split PCI error reset handler")
> Co-developed-by: Karen Ostrowska <karen.ostrowska@...el.com>
> Signed-off-by: Karen Ostrowska <karen.ostrowska@...el.com>
> Co-developed-by: Mateusz Palczewski <mateusz.palczewski@...el.com>
> Signed-off-by: Mateusz Palczewski <mateusz.palczewski@...el.com>
> Reviewed-by: Drewek Wojciech <wojciech.drewek@...el.com>
> Reviewed-by: Kitszel Przemyslaw <przemyslaw.kitszel@...el.com>
> Signed-off-by: Andrii Staikov <andrii.staikov@...el.com>

The ice driver recently started caching the PCI device structure
pointers in their VF structure instead of having to do this sort of
lookup on the fly.

See 31642d2854e2 ("ice: store VF's pci_dev ptr in ice_vf") [1][2]

[1]:
https://lore.kernel.org/intel-wired-lan/20230912115626.105828-1-mateusz.polchlopek@intel.com/
[2]:
https://lore.kernel.org/netdev/20231019173227.3175575-4-jacob.e.keller@intel.com/

Can we do something similar for i40e?

> ---
> v1 -> v2: Fix signed-off tags
> https://patchwork.ozlabs.org/project/intel-wired-lan/patch/20231204131041.3369693-1-andrii.staikov@intel.com/
> 
> v2 -> v3: use @vf_dev in pci_get_device() instead of NULL and remove unnecessary call
> https://patchwork.ozlabs.org/project/intel-wired-lan/patch/20231206125127.218350-1-andrii.staikov@intel.com/
> 
> v3 -> v4: wrap the added functionality into the CONFIG_PCI_IOV define as
> this is VF-related functionality
> ---
>  drivers/net/ethernet/intel/i40e/i40e_main.c   |  3 +++
>  .../ethernet/intel/i40e/i40e_virtchnl_pf.c    | 26 +++++++++++++++++++
>  .../ethernet/intel/i40e/i40e_virtchnl_pf.h    |  3 +++
>  3 files changed, 32 insertions(+)
> 
> diff --git a/drivers/net/ethernet/intel/i40e/i40e_main.c b/drivers/net/ethernet/intel/i40e/i40e_main.c
> index 7bb1f64833eb..bbe2d115fb15 100644
> --- a/drivers/net/ethernet/intel/i40e/i40e_main.c
> +++ b/drivers/net/ethernet/intel/i40e/i40e_main.c
> @@ -16513,6 +16513,9 @@ static void i40e_pci_error_reset_done(struct pci_dev *pdev)
>  		return;
>  
>  	i40e_reset_and_rebuild(pf, false, false);
> +#ifdef CONFIG_PCI_IOV
> +	i40e_restore_all_vfs_msi_state(pdev);
> +#endif /* CONFIG_PCI_IOV */
>  }
>  
>  /**
> diff --git a/drivers/net/ethernet/intel/i40e/i40e_virtchnl_pf.c b/drivers/net/ethernet/intel/i40e/i40e_virtchnl_pf.c
> index 3f99eb198245..d60f5419d6bd 100644
> --- a/drivers/net/ethernet/intel/i40e/i40e_virtchnl_pf.c
> +++ b/drivers/net/ethernet/intel/i40e/i40e_virtchnl_pf.c
> @@ -154,6 +154,32 @@ void i40e_vc_notify_reset(struct i40e_pf *pf)
>  			     (u8 *)&pfe, sizeof(struct virtchnl_pf_event));
>  }
>  
> +#ifdef CONFIG_PCI_IOV

Also noticed that i40e_virtchnl_pf.c is compiled always instead of only
conditionally when CONFIG_PCI_IOV is enabled. That's not really the
fault of this change, but I think it would be good cleanup to avoid
needing to compile any of this code if CONFIG_PCI_IOV is disabled.

> +void i40e_restore_all_vfs_msi_state(struct pci_dev *pdev)
> +{
> +	u16 vf_id;
> +	u16 pos;
> +
> +	/* Continue only if this is a PF */
> +	if (!pdev->is_physfn)
> +		return;
> +

The function could also just pass the pf instead of pdev, and we'd know
its the physical function.

> +	if (!pci_num_vf(pdev))
> +		return;

If we switch to saving pdevs in our VF structure, this could be a simple
iteration loop that does nothing if the number of VFs is 0.

> +
> +	pos = pci_find_ext_capability(pdev, PCI_EXT_CAP_ID_SRIOV);
> +	if (pos) {
> +		struct pci_dev *vf_dev = NULL;
> +
> +		pci_read_config_word(pdev, pos + PCI_SRIOV_VF_DID, &vf_id);
> +		while ((vf_dev = pci_get_device(pdev->vendor, vf_id, vf_dev))) {
> +			if (vf_dev->is_virtfn && vf_dev->physfn == pdev)
> +				pci_restore_msi_state(vf_dev);
> +		}
> +	}
> +}
> +#endif /* CONFIG_PCI_IOV */
> +

Thanks,
Jake