linux-kernel - Re: [PATCH V2] PCI: pciehp: Disable ACS Source Validation during hot-remove

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Message-ID: <20230214233016.GA3095090@bhelgaas>
Date:   Tue, 14 Feb 2023 17:30:16 -0600
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Vidya Sagar <vidyas@...dia.com>
Cc:     bhelgaas@...gle.com, treding@...dia.com, jonathanh@...dia.com,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        vsethi@...dia.com, kthota@...dia.com, mmaddireddy@...dia.com,
        sagar.tv@...il.com, Lukas Wunner <lukas@...ner.de>,
        Alex Williamson <alex.williamson@...hat.com>
Subject: Re: [PATCH V2] PCI: pciehp: Disable ACS Source Validation during
 hot-remove

[+cc Lukas, Alex for pciehp and ACS comments]

On Thu, Jan 12, 2023 at 12:35:33AM +0530, Vidya Sagar wrote:
> PCIe 6.0, 6.12.1.1 specifies that downstream devices are permitted to
> send upstream messages before they have been assigned a bus number and
> such messages have a Requester ID with Bus number set to 00h.
> If the Downstrem port has ACS Source Validation enabled, these messages
> will be detected as ACS violation error.
> Hence, disable ACS Source Validation in the bridge device during
> hot-remove operation and re-enable it after enumeration of the
> downstream hierarchy but before binding the respective device drivers.

s/Downstrem/Downstream/

Format as paragraphs (blank line between).

> Signed-off-by: Vidya Sagar <vidyas@...dia.com>
> ---
> v2:
> * Fixed build issues
> 
>  drivers/pci/hotplug/pciehp_pci.c | 13 ++++++++++++-
>  drivers/pci/pci.c                | 22 ++++++++++++++++++++++
>  include/linux/pci.h              |  6 ++++++
>  3 files changed, 40 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/pci/hotplug/pciehp_pci.c b/drivers/pci/hotplug/pciehp_pci.c
> index d17f3bf36f70..ad90bcf3f621 100644
> --- a/drivers/pci/hotplug/pciehp_pci.c
> +++ b/drivers/pci/hotplug/pciehp_pci.c
> @@ -63,6 +63,7 @@ int pciehp_configure_device(struct controller *ctrl)
>  
>  	pci_assign_unassigned_bridge_resources(bridge);
>  	pcie_bus_configure_settings(parent);
> +	pci_configure_acs_sv(bridge, true);
>  	pci_bus_add_devices(parent);
>  
>   out:
> @@ -117,6 +118,16 @@ void pciehp_unconfigure_device(struct controller *ctrl, bool presence)
>  		}
>  		pci_dev_put(dev);
>  	}
> -
> +	/*
> +	 * PCIe 6.0, 6.12.1.1 specifies that downstream devices are permitted
> +	 * to send upstream messages before they have been assigned a bus
> +	 * number and such messages have a Requester ID with Bus number
> +	 * set to 00h. If the Downstrem port has ACS Source Validation enabled,

s/Downstrem/Downstream/

> +	 * these messages will be detected as ACS violation error.
> +	 * Hence, disable ACS Source Validation here and re-enable it after
> +	 * enumeration of the downstream hierarchy and before binding the
> +	 * respective device drivers in pciehp_configure_device().
> +	 */
> +	pci_configure_acs_sv(ctrl->pcie->port, false);

What if we have a slot that's empty at boot and we add a device later?
It looks like we still might see ACS errors there because the add
happens before a remove?

>  	pci_unlock_rescan_remove();
>  }
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index 95bc329e74c0..9cefaf814f49 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -991,6 +991,28 @@ static void pci_enable_acs(struct pci_dev *dev)
>  	pci_disable_acs_redir(dev);
>  }
>  
> +#ifdef CONFIG_HOTPLUG_PCI_PCIE
> +void pci_configure_acs_sv(struct pci_dev *dev, bool flag)
> +{
> +	u16 cap;
> +	u16 ctrl;
> +
> +	if (!pci_acs_enable || !dev->acs_cap)
> +		return;
> +
> +	pci_read_config_word(dev, dev->acs_cap + PCI_ACS_CAP, &cap);
> +	pci_read_config_word(dev, dev->acs_cap + PCI_ACS_CTRL, &ctrl);
> +
> +	if (flag)
> +		ctrl |= (cap & PCI_ACS_SV);
> +	else
> +		ctrl &= ~(cap & PCI_ACS_SV);
> +
> +	pci_write_config_word(dev, dev->acs_cap + PCI_ACS_CTRL, ctrl);

I guess we don't have a way to do this for the non-standard ACS-like
devices, i.e., pci_dev_specific_enable_acs().  Not the end of the
world, just unfortunate that we'll have different behavior there.

> +}
> +EXPORT_SYMBOL_GPL(pci_configure_acs_sv);

Doesn't seem like this needs to be exported or exposed via
linux/pci.h.  pciehp cannot be built as a module.

> +#endif
> +
>  /**
>   * pci_restore_bars - restore a device's BAR values (e.g. after wake-up)
>   * @dev: PCI device to have its BARs restored
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index 060af91bafcd..edf516e39764 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -2239,6 +2239,12 @@ void pci_hp_create_module_link(struct pci_slot *pci_slot);
>  void pci_hp_remove_module_link(struct pci_slot *pci_slot);
>  #endif
>  
> +#ifdef CONFIG_HOTPLUG_PCI_PCIE
> +void pci_configure_acs_sv(struct pci_dev *dev, bool flag);
> +#else
> +static inline void pci_configure_acs_sv(struct pci_dev *dev, bool flag) { }
> +#endif
> +
>  /**
>   * pci_pcie_cap - get the saved PCIe capability offset
>   * @dev: PCI device
> -- 
> 2.17.1
>