This is a note to let you know that I've just added the patch titled powerpc/pseries: Don't enforce MSI affinity with kdump to the 5.10-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: powerpc-pseries-don-t-enforce-msi-affinity-with-kdump.patch and it can be found in the queue-5.10 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From f9619d5e5174867536b7e558683bc4408eab833f Mon Sep 17 00:00:00 2001 From: Greg Kurz <groug@xxxxxxxx> Date: Mon, 15 Feb 2021 10:45:06 +0100 Subject: powerpc/pseries: Don't enforce MSI affinity with kdump MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit From: Greg Kurz <groug@xxxxxxxx> commit f9619d5e5174867536b7e558683bc4408eab833f upstream. Depending on the number of online CPUs in the original kernel, it is likely for CPU #0 to be offline in a kdump kernel. The associated IRQs in the affinity mappings provided by irq_create_affinity_masks() are thus not started by irq_startup(), as per-design with managed IRQs. This can be a problem with multi-queue block devices driven by blk-mq : such a non-started IRQ is very likely paired with the single queue enforced by blk-mq during kdump (see blk_mq_alloc_tag_set()). This causes the device to remain silent and likely hangs the guest at some point. This is a regression caused by commit 9ea69a55b3b9 ("powerpc/pseries: Pass MSI affinity to irq_create_mapping()"). Note that this only happens with the XIVE interrupt controller because XICS has a workaround to bypass affinity, which is activated during kdump with the "noirqdistrib" kernel parameter. The issue comes from a combination of factors: - discrepancy between the number of queues detected by the multi-queue block driver, that was used to create the MSI vectors, and the single queue mode enforced later on by blk-mq because of kdump (i.e. keeping all queues fixes the issue) - CPU#0 offline (i.e. kdump always succeed with CPU#0) Given that I couldn't reproduce on x86, which seems to always have CPU#0 online even during kdump, I'm not sure where this should be fixed. Hence going for another approach : fine-grained affinity is for performance and we don't really care about that during kdump. Simply revert to the previous working behavior of ignoring affinity masks in this case only. Fixes: 9ea69a55b3b9 ("powerpc/pseries: Pass MSI affinity to irq_create_mapping()") Cc: stable@xxxxxxxxxxxxxxx # v5.10+ Signed-off-by: Greg Kurz <groug@xxxxxxxx> Reviewed-by: Laurent Vivier <lvivier@xxxxxxxxxx> Reviewed-by: Cédric Le Goater <clg@xxxxxxxx> Signed-off-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx> Link: https://lore.kernel.org/r/20210215094506.1196119-1-groug@xxxxxxxx Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- arch/powerpc/platforms/pseries/msi.c | 25 +++++++++++++++++++++++-- 1 file changed, 23 insertions(+), 2 deletions(-) --- a/arch/powerpc/platforms/pseries/msi.c +++ b/arch/powerpc/platforms/pseries/msi.c @@ -4,6 +4,7 @@ * Copyright 2006-2007 Michael Ellerman, IBM Corp. */ +#include <linux/crash_dump.h> #include <linux/device.h> #include <linux/irq.h> #include <linux/msi.h> @@ -458,8 +459,28 @@ again: return hwirq; } - virq = irq_create_mapping_affinity(NULL, hwirq, - entry->affinity); + /* + * Depending on the number of online CPUs in the original + * kernel, it is likely for CPU #0 to be offline in a kdump + * kernel. The associated IRQs in the affinity mappings + * provided by irq_create_affinity_masks() are thus not + * started by irq_startup(), as per-design for managed IRQs. + * This can be a problem with multi-queue block devices driven + * by blk-mq : such a non-started IRQ is very likely paired + * with the single queue enforced by blk-mq during kdump (see + * blk_mq_alloc_tag_set()). This causes the device to remain + * silent and likely hangs the guest at some point. + * + * We don't really care for fine-grained affinity when doing + * kdump actually : simply ignore the pre-computed affinity + * masks in this case and let the default mask with all CPUs + * be used when creating the IRQ mappings. + */ + if (is_kdump_kernel()) + virq = irq_create_mapping(NULL, hwirq); + else + virq = irq_create_mapping_affinity(NULL, hwirq, + entry->affinity); if (!virq) { pr_debug("rtas_msi: Failed mapping hwirq %d\n", hwirq); Patches currently in stable-queue which might be from groug@xxxxxxxx are queue-5.10/powerpc-pseries-don-t-enforce-msi-affinity-with-kdump.patch