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[34.142.255.199]) by smtp.gmail.com with ESMTPSA id 5a478bee46e88-3074db528dcsm12388863eec.3.2026.06.06.03.08.33 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 06 Jun 2026 03:08:38 -0700 (PDT) Date: Sat, 6 Jun 2026 10:08:28 +0000 From: Pranjal Shrivastava To: David Matlack Cc: kexec@lists.infradead.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-pci@vger.kernel.org, Adithya Jayachandran , Alexander Graf , Alex Williamson , Bjorn Helgaas , Chris Li , David Rientjes , Jacob Pan , Jason Gunthorpe , Jonathan Corbet , Josh Hilke , Leon Romanovsky , Lukas Wunner , Mike Rapoport , Parav Pandit , Pasha Tatashin , Pratyush Yadav , Saeed Mahameed , Samiullah Khawaja , Shuah Khan , Vipin Sharma , William Tu , Yi Liu Subject: Re: [PATCH v6 03/12] PCI: liveupdate: Track incoming preserved PCI devices Message-ID: References: <20260522202410.3104264-1-dmatlack@google.com> <20260522202410.3104264-4-dmatlack@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260522202410.3104264-4-dmatlack@google.com> On Fri, May 22, 2026 at 08:24:01PM +0000, David Matlack wrote: > During PCI enumeration, the previous kernel might have passed state about > devices that were preserved across kexec. The PCI core needs to fetch > this state to identify which devices are "incoming" and require special > handling. > > Add pci_liveupdate_setup_device() which is called during device setup > to fetch the serialized state (struct pci_ser) from the Live Update > Orchestrator. The first time this happens, pci_flb_retrieve() will run > and convert the array of pci_dev_ser structs into an xarray so that it > can be looked up efficiently. > > If a device is found in the xarray, the PCI core stores a pointer to its > state in dev->liveupdate_incoming and holds a reference to the incoming > FLB until pci_liveupdate_finish() is called by the driver. > > This ensures proper lifecycle management for incoming preserved devices > and allows the PCI core and drivers to apply specific Live Update > logic to them in subsequent commits. > > Drivers can check if a device is an incoming preserved device (e.g. > during probe) by calling pci_liveupdate_is_incoming(). > > CONFIG_64BIT is now required to enable CONFIG_PCI_LIVEUPDATE so that the > domain and bdf can be guaranteed to fit in an unsigned long and be used > as the xarray key. > > Signed-off-by: David Matlack > --- > MAINTAINERS | 1 + > drivers/pci/Kconfig | 2 +- > drivers/pci/liveupdate.c | 230 ++++++++++++++++++++++++++++++++- > drivers/pci/liveupdate.h | 5 + > drivers/pci/probe.c | 3 + > include/linux/pci_liveupdate.h | 13 ++ > 6 files changed, 251 insertions(+), 3 deletions(-) > > diff --git a/MAINTAINERS b/MAINTAINERS > index 6c618830cf61..0e262c0ceb43 100644 > --- a/MAINTAINERS > +++ b/MAINTAINERS > @@ -20537,6 +20537,7 @@ L: linux-pci@vger.kernel.org > S: Maintained > T: git git://git.kernel.org/pub/scm/linux/kernel/git/liveupdate/linux.git > F: drivers/pci/liveupdate.c > +F: drivers/pci/liveupdate.h > F: include/linux/kho/abi/pci.h > F: include/linux/pci_liveupdate.h > > diff --git a/drivers/pci/Kconfig b/drivers/pci/Kconfig > index 10c9b65aa242..e68ae5c172d4 100644 > --- a/drivers/pci/Kconfig > +++ b/drivers/pci/Kconfig > @@ -330,7 +330,7 @@ config VGA_ARB_MAX_GPUS > > config PCI_LIVEUPDATE > bool "PCI Live Update Support" > - depends on PCI && LIVEUPDATE > + depends on PCI && LIVEUPDATE && 64BIT I see that the static assertions in Patch 1 work because of the 64BIT enforcement here. In that case, should we have the assertions check u64? > help > Enable PCI core support for preserving PCI devices across Live > Update. This, in combination with support in a device's driver, > [...] > static int pci_flb_retrieve(struct liveupdate_flb_op_args *args) > { > - args->obj = phys_to_virt(args->data); > + struct pci_ser *ser = phys_to_virt(args->data); > + struct pci_flb_incoming *incoming; > + int ret = -ENOMEM; > + u32 i; > + > + incoming = kmalloc_obj(*incoming); > + if (!incoming) > + goto err_restore_free; > + > + incoming->ser = ser; > + xa_init(&incoming->xa); > + > + for (i = 0; i < incoming->ser->max_nr_devices; i++) { > + struct pci_dev_ser *dev_ser = &incoming->ser->devices[i]; > + unsigned long key; > + > + if (!dev_ser->refcount) > + continue; > + > + key = pci_ser_xa_key(dev_ser->domain, dev_ser->bdf); > + ret = xa_insert(&incoming->xa, key, dev_ser, GFP_KERNEL); > + if (ret) > + goto err_xa_destroy; > + } > + > + args->obj = incoming; > return 0; > + > +err_xa_destroy: > + xa_destroy(&incoming->xa); > + kfree(incoming); > +err_restore_free: > + kho_restore_free(ser); I tend to partly agree with Sashiko[1] here.. it raises a policy-hole. We may need a policy here, the options I have in mind are: 1. Retrieve shall ONLY be tried once, if it fails (like -ENOMEM in the xArray alloc), it's a liveupdate failure. We can't retry liveupdate. 2. Retrying retrieve is allowed. The only downside with option 1 is, the user may want flexibility due to certain subsystems OR may choose NOT to use the proposed LUOd and instead have its own user-space component which might try funny things or have a different use-case. In such a situation, the system may have transiently run out of memory during the kexec transition (for e.g. a subsystem uses GFP_ATOMIC to allocate memory and temporarily runs out of the atomic pool). [Note we removed it in IOMMU v1 [2] but subsystems may have a use-case for it] If the kernel frees the KHO page on the first failure, it removes any chance of recovery. :/ Thus, it might make sense to let the user decide if it wants to fail the liveupdate or retry again based on the failure type / source? [...] The changes LGTM, except for policy-based, kho_restore_free discussion. Reviewed-by: Pranjal Shrivastava Thanks, Praan [1] https://lore.kernel.org/all/20260522211333.D56A21F000E9@smtp.kernel.org/ [2] https://lore.kernel.org/all/20260203220948.2176157-2-skhawaja@google.com/