linux-kernel - Re: [PATCH 02/21] PCI: Add API to track PCI devices preserved across Live Update

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Message-ID: <CA+CK2bAMTwxGLK4_ayvkgEMEmr2WmqPe7KSjhZzdz7fuTp2naA@mail.gmail.com>
Date: Mon, 1 Dec 2025 16:23:30 -0500
From: Pasha Tatashin <pasha.tatashin@...een.com>
To: Jason Gunthorpe <jgg@...dia.com>
Cc: Lukas Wunner <lukas@...ner.de>, David Matlack <dmatlack@...gle.com>, 
	Alex Williamson <alex@...zbot.org>, Adithya Jayachandran <ajayachandra@...dia.com>, Alex Mastro <amastro@...com>, 
	Alistair Popple <apopple@...dia.com>, Andrew Morton <akpm@...ux-foundation.org>, 
	Bjorn Helgaas <bhelgaas@...gle.com>, Chris Li <chrisl@...nel.org>, 
	David Rientjes <rientjes@...gle.com>, Jacob Pan <jacob.pan@...ux.microsoft.com>, 
	Josh Hilke <jrhilke@...gle.com>, Kevin Tian <kevin.tian@...el.com>, kvm@...r.kernel.org, 
	Leon Romanovsky <leonro@...dia.com>, linux-kernel@...r.kernel.org, 
	linux-kselftest@...r.kernel.org, linux-pci@...r.kernel.org, 
	Mike Rapoport <rppt@...nel.org>, Parav Pandit <parav@...dia.com>, 
	Philipp Stanner <pstanner@...hat.com>, Pratyush Yadav <pratyush@...nel.org>, 
	Saeed Mahameed <saeedm@...dia.com>, Samiullah Khawaja <skhawaja@...gle.com>, Shuah Khan <shuah@...nel.org>, 
	Tomita Moeko <tomitamoeko@...il.com>, Vipin Sharma <vipinsh@...gle.com>, William Tu <witu@...dia.com>, 
	Yi Liu <yi.l.liu@...el.com>, Yunxiang Li <Yunxiang.Li@....com>, 
	Zhu Yanjun <yanjun.zhu@...ux.dev>
Subject: Re: [PATCH 02/21] PCI: Add API to track PCI devices preserved across
 Live Update

> > > So while what you say is all technically true, I'm not sure this is
> > > necessary.
> >
> > I agree. However, Lukas's comment made me wonder about the future: if
> > we eventually need to preserve non-PCI devices (like a TPM), should we
> > be designing a common identification mechanism for all buses now? Or
> > should we settle on BDF for PCI and invent stable identifiers for
> > other bus types as they become necessary?
>
> Well, at least PCI subsystem should use BDF..

BDF must be stable for PCI live update to work correctly.

> You are probably right that the matching of preserved data to a struct
> device should be more general though.

Right, we need a mechanism to ensure early in boot that any preserved
device does not auto-bind to a driver later in boot.

Using the UEFI Device Path format seems like a good way not to
re-invent something that already exists.  For example, while a
preserved PCI device looks like this:
Acpi(PNP0A03,0)/Pci(1E|0)/Pci(0|0) (Luka's example)

We can seamlessly support other device types later using their native
paths without changing the identification schema:

TPM: Acpi(PNP0C31,0)
IPMI/BMC: Acpi(PNP0A03,0)/Pci(1F|0)/BMC(1,0xCA2)
NVMe (PCI-attached): Acpi(PNP0A03,0)/Pci(1C|0)/Pci(0|0)/NVMe(1,00-00-...)
etc...

Pasha