linux-kernel - [PATCH] arch/x86: Don't try to poke disabled/non-existent APIC

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Date:   Sat, 22 Oct 2016 05:18:04 +0300
From:   ville.syrjala@...ux.intel.com
To:     linux-kernel@...r.kernel.org
Cc:     stable@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        Prarit Bhargava <prarit@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Len Brown <len.brown@...el.com>, Borislav Petkov <bp@...e.de>,
        Andi Kleen <ak@...ux.intel.com>, Jiri Olsa <jolsa@...hat.com>,
        Juergen Gross <jgross@...e.com>, dyoung@...hat.com,
        Eric Biederman <ebiederm@...ssion.com>,
        kexec@...ts.infradead.org, Thomas Gleixner <tglx@...utronix.de>,
        Ville Syrjälä 
        <ville.syrjala@...ux.intel.com>
Subject: [PATCH] arch/x86: Don't try to poke disabled/non-existent APIC

From: Ville Syrjälä <ville.syrjala@...ux.intel.com>

Apparently trying to poke a disabled or non-existent APIC
leads to a box that doesn't even boot. Let's not do that.

No real clue if this is the right fix, but at least my
P3 machine boots again.

Cc: stable@...r.kernel.org
Cc: Ingo Molnar <mingo@...hat.com>
Cc: "H. Peter Anvin" <hpa@...or.com>
Cc: x86@...nel.org
Cc: Prarit Bhargava <prarit@...hat.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Len Brown <len.brown@...el.com>
Cc: Borislav Petkov <bp@...e.de>
Cc: Andi Kleen <ak@...ux.intel.com>
Cc: Jiri Olsa <jolsa@...hat.com>
Cc: Juergen Gross <jgross@...e.com>
Cc: dyoung@...hat.com
Cc: Eric Biederman <ebiederm@...ssion.com>
Cc: kexec@...ts.infradead.org
Cc: Thomas Gleixner <tglx@...utronix.de>
Fixes: 2a51fe083eba ("arch/x86: Handle non enumerated CPU after physical hotplug")
Signed-off-by: Ville Syrjälä <ville.syrjala@...ux.intel.com>
---
 arch/x86/kernel/smpboot.c | 16 +++++++++-------
 1 file changed, 9 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index 951f093a96fe..42f5eb7b4f6c 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -1409,15 +1409,17 @@ __init void prefill_possible_map(void)
 
 	/* 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();
+		if (boot_cpu_has(X86_FEATURE_APIC)) {
+			int apicid = boot_cpu_physical_apicid;
+			int cpu = hard_smp_processor_id();
 
-		pr_warn("Boot CPU (id %d) not listed by BIOS\n", cpu);
+			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);
+			/* 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;
-- 
2.7.4