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[PATCH 4.7 23/31] arch/x86: Handle non enumerated CPU after physical hotplug

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4.7-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Prarit Bhargava <prarit@redhat.com>

commit 2a51fe083eba7f99cbda72f5ef90cdf2f4df882c upstream.

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 <prarit@redhat.com>
Fixes: 1f12e32f4cd5 ("x86/topology: Create logical package id")
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Len Brown <len.brown@intel.com>
Cc: Borislav Petkov <bp@suse.de>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: dyoung@redhat.com
Cc: Eric Biederman <ebiederm@xmission.com>
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 <tglx@linutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 arch/x86/kernel/smpboot.c |   18 +++++++++++++++---
 1 file changed, 15 insertions(+), 3 deletions(-)

--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -1393,9 +1393,21 @@ __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) {

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[PATCH 4.7 00/31] 4.7.8-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-10-14 15:00 +0200
  [PATCH 4.7 17/31] KVM: PPC: BookE: Fix a sanity check Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-10-14 15:00 +0200
  [PATCH 4.7 01/31] powerpc/pseries: use pci_host_bridge.release_fn() to kfree(phb) Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-10-14 15:00 +0200
  [PATCH 4.7 23/31] arch/x86: Handle non enumerated CPU after physical hotplug Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-10-14 15:20 +0200
  [PATCH 4.7 19/31] x86/boot: Fix kdump, cleanup aborted E820_PRAM max_pfn manipulation Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-10-14 15:20 +0200
  [PATCH 4.7 22/31] x86/apic: Get rid of apic_version[] array Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-10-14 15:20 +0200
  [PATCH 4.7 05/31] ALSA: ali5451: Fix out-of-bound position reporting Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-10-14 15:20 +0200
  [PATCH 4.7 31/31] tpm_crb: fix crb_req_canceled behavior Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-10-14 15:20 +0200
  [PATCH 4.7 26/31] ARM: dts: mvebu: armada-390: add missing compatibility string and bracket Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-10-14 15:40 +0200
  [PATCH 4.7 09/31] mfd: atmel-hlcdc: Do not sleep in atomic context Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-10-14 15:40 +0200
  [PATCH 4.7 28/31] ARM: cpuidle: Fix error return code Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-10-14 15:40 +0200
  [PATCH 4.7 16/31] KVM: arm/arm64: vgic: Dont flush/sync without a working vgic Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-10-14 15:40 +0200
  [PATCH 4.7 07/31] ALSA: usb-line6: use the same declaration as definition in header for MIDI manufacturer ID Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-10-14 15:40 +0200
  [PATCH 4.7 10/31] mfd: 88pm80x: Double shifting bug in suspend/resume Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-10-14 15:40 +0200
  Re: [PATCH 4.7 00/31] 4.7.8-stable review Shuah Khan <shuah.kh@samsung.com> - 2016-10-14 21:00 +0200
  Re: [PATCH 4.7 00/31] 4.7.8-stable review Guenter Roeck <linux@roeck-us.net> - 2016-10-14 21:30 +0200

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