Merge branch 'x86-apic-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull x86/apic changes from Ingo Molnar:
 "Two main changes:

   - improve local APIC Error Status Register reporting robustness

   - add the 'disable_cpu_apicid=x' boot parameter for kexec booting"

* 'x86-apic-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  x86, apic: Make disabled_cpu_apicid static read_mostly, fix typos
  x86, apic, kexec: Add disable_cpu_apicid kernel parameter
  x86/apic: Read Error Status Register correctly

2 files changed, 66 insertions, 9 deletions

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 0940078edebb..3b8e262c3657 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -774,6 +774,15 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
         disable=        [IPV6]
                         See Documentation/networking/ipv6.txt.
 
+        disable_cpu_apicid= [X86,APIC,SMP]
+                        Format: <int>
+                        The number of initial APIC ID for the
+                        corresponding CPU to be disabled at boot,
+                        mostly used for the kdump 2nd kernel to
+                        disable BSP to wake up multiple CPUs without
+                        causing system reset or hang due to sending
+                        INIT from AP to BSP.
+
         disable_ddw     [PPC/PSERIES]
                         Disable Dynamic DMA Window support. Use this if
                         to workaround buggy firmware.
diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
index d278736bf774..7f26c9a70a9e 100644
--- a/arch/x86/kernel/apic/apic.c
+++ b/arch/x86/kernel/apic/apic.c
@@ -75,6 +75,13 @@ unsigned int max_physical_apicid;
 physid_mask_t phys_cpu_present_map;
 
 /*
+ * Processor to be disabled specified by kernel parameter
+ * disable_cpu_apicid=<int>, mostly used for the kdump 2nd kernel to
+ * avoid undefined behaviour caused by sending INIT from AP to BSP.
+ */
+static unsigned int disabled_cpu_apicid __read_mostly = BAD_APICID;
+
+/*
  * Map cpu index to physical APIC ID
  */
 DEFINE_EARLY_PER_CPU_READ_MOSTLY(u16, x86_cpu_to_apicid, BAD_APICID);
@@ -1968,7 +1975,7 @@ __visible void smp_trace_spurious_interrupt(struct pt_regs *regs)
  */
 static inline void __smp_error_interrupt(struct pt_regs *regs)
 {
-        u32 v0, v1;
+        u32 v;
         u32 i = 0;
         static const char * const error_interrupt_reason[] = {
                 "Send CS error",                /* APIC Error Bit 0 */
@@ -1982,21 +1989,20 @@ static inline void __smp_error_interrupt(struct pt_regs *regs)
         };
 
         /* First tickle the hardware, only then report what went on. -- REW */
-        v0 = apic_read(APIC_ESR);
         apic_write(APIC_ESR, 0);
-        v1 = apic_read(APIC_ESR);
+        v = apic_read(APIC_ESR);
         ack_APIC_irq();
         atomic_inc(&irq_err_count);
 
-        apic_printk(APIC_DEBUG, KERN_DEBUG "APIC error on CPU%d: %02x(%02x)",
-                    smp_processor_id(), v0 , v1);
+        apic_printk(APIC_DEBUG, KERN_DEBUG "APIC error on CPU%d: %02x",
+                    smp_processor_id(), v);
 
-        v1 = v1 & 0xff;
-        while (v1) {
-                if (v1 & 0x1)
+        v &= 0xff;
+        while (v) {
+                if (v & 0x1)
                         apic_printk(APIC_DEBUG, KERN_CONT " : %s", error_interrupt_reason[i]);
                 i++;
-                v1 >>= 1;
+                v >>= 1;
         }
 
         apic_printk(APIC_DEBUG, KERN_CONT "\n");
@@ -2115,6 +2121,39 @@ int generic_processor_info(int apicid, int version)
                                 phys_cpu_present_map);
 
         /*
+         * boot_cpu_physical_apicid is designed to have the apicid
+         * returned by read_apic_id(), i.e, the apicid of the
+         * currently booting-up processor. However, on some platforms,
+         * it is temporarily modified by the apicid reported as BSP
+         * through MP table. Concretely:
+         *
+         * - arch/x86/kernel/mpparse.c: MP_processor_info()
+         * - arch/x86/mm/amdtopology.c: amd_numa_init()
+         * - arch/x86/platform/visws/visws_quirks.c: MP_processor_info()
+         *
+         * This function is executed with the modified
+         * boot_cpu_physical_apicid. So, disabled_cpu_apicid kernel
+         * parameter doesn't work to disable APs on kdump 2nd kernel.
+         *
+         * Since fixing handling of boot_cpu_physical_apicid requires
+         * another discussion and tests on each platform, we leave it
+         * for now and here we use read_apic_id() directly in this
+         * function, generic_processor_info().
+         */
+        if (disabled_cpu_apicid != BAD_APICID &&
+            disabled_cpu_apicid != read_apic_id() &&
+            disabled_cpu_apicid == apicid) {
+                int thiscpu = num_processors + disabled_cpus;
+
+                pr_warning("APIC: Disabling requested cpu."
+                           " Processor %d/0x%x ignored.\n",
+                           thiscpu, apicid);
+
+                disabled_cpus++;
+                return -ENODEV;
+        }
+
+        /*
          * If boot cpu has not been detected yet, then only allow upto
          * nr_cpu_ids - 1 processors and keep one slot free for boot cpu
          */
@@ -2592,3 +2631,12 @@ static int __init lapic_insert_resource(void)
  * that is using request_resource
  */
 late_initcall(lapic_insert_resource);
+
+static int __init apic_set_disabled_cpu_apicid(char *arg)
+{
+        if (!arg || !get_option(&arg, &disabled_cpu_apicid))
+                return -EINVAL;
+
+        return 0;
+}
+early_param("disable_cpu_apicid", apic_set_disabled_cpu_apicid);