Re: [PATCH v2] powerpc/rtas_pci: No hotplug on permanently removed device on pSeries

[tasmiya <tasmiya@linux.ibm.com>]

Greetings,

Tested-by: Tasmiya Nalatwad <tasmiya@linux.ibm.com>
Reported-by: Tasmiya Nalatwad <tasmiya@linux.ibm.com>


I have Tested this patch in my KVM guest environment with device 
passthrough via vfio, It works fine and fixes the issue.
Triggered EEH freeze beyond eeh_max_freezes to permanently remove the 
device, then hotplugged a new PCI device. Without the patch, the rescan 
attempted to bring back the permanently removed device. With the patch 
applied, the removed device is correctly skipped during rescan and only 
newly hotplugged device is seen in the guest.


Thank you,

Tasmiya


On 26/06/26 2:43 pm, Shivaprasad G Bhat wrote:
> The eeh_driver disables and offlines the PE permanently when it
> exceeds the freeze count beyond eeh_max_freeze within the last hour.
> The PE is only offline, so the device tree entries, eeh device
> references are all intact till the real unplug of the device from
> the guest/host takes place.
>
> On pSeries, with a new hotplug of any PCI device, the drmgr initiates
> a system-wide PCI rescan, which finds devices offlined by the eeh_driver
> and there will be attempts to bring them online. This leads to
> recurring EEHs either at the config read time itself or a bit
> later depending on the type of the problem.
>
> For PowerNV, the commit d2b0f6f77ee5 ("powerpc/eeh: No hotplug on
> permanently removed dev") introduced the EEH_DEV_REMOVED flag to
> prevent such inadvertent rescans on hierarchical toplogies relavent in
> Baremetal setups. For pSeries, such topologies don't really make sense
> as the devices are either part of the same PE OR exposed as independent
> devices on multiple virtual PHBs. However, the inadvertent rescans are
> still a possibility with either hotplug of a new device or otherwise
> with manual system-wide pci bus rescan attempts.
>
> So the patch checks for EEH_DEV_REMOVED before allowing config space
> access just like PowerNV, making the PCI core omit the PE, and thus
> preventing subsequent EEH recurances. The patch is tested on PowerVM
> and KVM machines with single and multi-function devices, and on the
> devices behind a switch. The unplug of the affected devices post EEH
> removal is also working fine as expected.
>
> Signed-off-by: Shivaprasad G Bhat <sbhat@linux.ibm.com>
> References: d2b0f6f77ee5 ("powerpc/eeh: No hotplug on permanently removed dev")
> ---
>   arch/powerpc/kernel/rtas_pci.c |    8 ++++++++
>   1 file changed, 8 insertions(+)
>
> diff --git a/arch/powerpc/kernel/rtas_pci.c b/arch/powerpc/kernel/rtas_pci.c
> index fccf96e897f6..206c825225c2 100644
> --- a/arch/powerpc/kernel/rtas_pci.c
> +++ b/arch/powerpc/kernel/rtas_pci.c
> @@ -54,6 +54,10 @@ int rtas_pci_dn_read_config(struct pci_dn *pdn, int where, int size, u32 *val)
>   	if (!config_access_valid(pdn, where))
>   		return PCIBIOS_BAD_REGISTER_NUMBER;
>   #ifdef CONFIG_EEH
> +	if (pdn->edev &&
> +	    (pdn->edev->mode & EEH_DEV_REMOVED))
> +		return PCIBIOS_DEVICE_NOT_FOUND;
> +
>   	if (pdn->edev && pdn->edev->pe &&
>   	    (pdn->edev->pe->state & EEH_PE_CFG_BLOCKED))
>   		return PCIBIOS_SET_FAILED;
> @@ -105,6 +109,10 @@ int rtas_pci_dn_write_config(struct pci_dn *pdn, int where, int size, u32 val)
>   	if (!config_access_valid(pdn, where))
>   		return PCIBIOS_BAD_REGISTER_NUMBER;
>   #ifdef CONFIG_EEH
> +	if (pdn->edev &&
> +	    (pdn->edev->mode & EEH_DEV_REMOVED))
> +		return PCIBIOS_DEVICE_NOT_FOUND;
> +
>   	if (pdn->edev && pdn->edev->pe &&
>   	    (pdn->edev->pe->state & EEH_PE_CFG_BLOCKED))
>   		return PCIBIOS_SET_FAILED;
>
>