linux-kernel - Re: [PATCH v3 03/10] PCI: Allow per function PCI slots

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Message-ID: <20250912122300.GA15517@p1gen4-pw042f0m.boeblingen.de.ibm.com>
Date: Fri, 12 Sep 2025 14:23:00 +0200
From: Benjamin Block <bblock@...ux.ibm.com>
To: Farhan Ali <alifm@...ux.ibm.com>
Cc: linux-s390@...r.kernel.org, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
        alex.williamson@...hat.com, helgaas@...nel.org, schnelle@...ux.ibm.com,
        mjrosato@...ux.ibm.com
Subject: Re: [PATCH v3 03/10] PCI: Allow per function PCI slots

On Thu, Sep 11, 2025 at 11:33:00AM -0700, Farhan Ali wrote:
> On s390 systems, which use a machine level hypervisor, PCI devices are
> always accessed through a form of PCI pass-through which fundamentally
> operates on a per PCI function granularity. This is also reflected in the
> s390 PCI hotplug driver which creates hotplug slots for individual PCI
> functions. Its reset_slot() function, which is a wrapper for
> zpci_hot_reset_device(), thus also resets individual functions.
> 
> Currently, the kernel's PCI_SLOT() macro assigns the same pci_slot object
> to multifunction devices. This approach worked fine on s390 systems that
> only exposed virtual functions as individual PCI domains to the operating
> system.  Since commit 44510d6fa0c0 ("s390/pci: Handling multifunctions")
> s390 supports exposing the topology of multifunction PCI devices by
> grouping them in a shared PCI domain. When attempting to reset a function
> through the hotplug driver, the shared slot assignment causes the wrong
> function to be reset instead of the intended one. It also leaks memory as
> we do create a pci_slot object for the function, but don't correctly free
> it in pci_slot_release().
> 
> Add a flag for struct pci_slot to allow per function PCI slots for
> functions managed through a hypervisor, which exposes individual PCI
> functions while retaining the topology.
> 
> Fixes: 44510d6fa0c0 ("s390/pci: Handling multifunctions")

Stable tag?
Reseting the wrong PCI function sounds bad enough.

-- 
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