From 2a51fe083eba7f99cbda72f5ef90cdf2f4df882c Mon Sep 17 00:00:00 2001 From: Prarit Bhargava Date: Mon, 3 Oct 2016 13:07:12 -0400 Subject: [PATCH] arch/x86: Handle non enumerated CPU after physical hotplug When a CPU is physically added to a system then the MADT table is not updated. If subsequently a kdump kernel is started on that physically added CPU then the ACPI enumeration fails to provide the information for this CPU which is now the boot CPU of the kdump kernel. As a consequence, generic_processor_info() is not invoked for that CPU so the number of enumerated processors is 0 and none of the initializations, including the logical package id management, are performed. We have code which relies on the correctness of the logical package map and other information which is initialized via generic_processor_info(). Executing such code will result in undefined behaviour or kernel crashes. This problem applies only to the kdump kernel because a normal kexec will switch to the original boot CPU, which is enumerated in MADT, before jumping into the kexec kernel. The boot code already has a check for num_processors equal 0 in prefill_possible_map(). We can use that check as an indicator that the enumeration of the boot CPU did not happen and invoke generic_processor_info() for it. That initializes the relevant data for the boot CPU and therefore prevents subsequent failure. [ tglx: Refined the code and rewrote the changelog ] Signed-off-by: Prarit Bhargava Fixes: 1f12e32f4cd5 ("x86/topology: Create logical package id") Cc: Peter Zijlstra Cc: Len Brown Cc: Borislav Petkov Cc: Andi Kleen Cc: Jiri Olsa Cc: Juergen Gross Cc: dyoung@redhat.com Cc: Eric Biederman Cc: kexec@lists.infradead.org Link: http://lkml.kernel.org/r/1475514432-27682-1-git-send-email-prarit@redhat.com Signed-off-by: Thomas Gleixner --- arch/x86/kernel/smpboot.c | 18 +++++++++++++++--- 1 file changed, 15 insertions(+), 3 deletions(-) diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c index 42a93621f5b0..951f093a96fe 100644 --- a/arch/x86/kernel/smpboot.c +++ b/arch/x86/kernel/smpboot.c @@ -1407,9 +1407,21 @@ __init void prefill_possible_map(void) { int i, possible; - /* no processor from mptable or madt */ - if (!num_processors) - num_processors = 1; + /* No boot processor was found in mptable or ACPI MADT */ + if (!num_processors) { + int apicid = boot_cpu_physical_apicid; + int cpu = hard_smp_processor_id(); + + pr_warn("Boot CPU (id %d) not listed by BIOS\n", cpu); + + /* Make sure boot cpu is enumerated */ + if (apic->cpu_present_to_apicid(0) == BAD_APICID && + apic->apic_id_valid(apicid)) + generic_processor_info(apicid, boot_cpu_apic_version); + + if (!num_processors) + num_processors = 1; + } i = setup_max_cpus ?: 1; if (setup_possible_cpus == -1) { -- 2.20.1