x86, apic: Handle a bad TSC more gracefully

If the TSC is unusable or disabled, then this patch fixes:

 - Confusion while trying to clear old APIC interrupts.
 - Division by zero and incorrect programming of the TSC deadline
   timer.

This fixes boot if the CPU has a TSC deadline timer but a missing or
broken TSC.  The failure to boot can be observed with qemu using
-cpu qemu64,-tsc,+tsc-deadline

This also happens to me in nested KVM for unknown reasons.
With this patch, I can boot cleanly (although without a TSC).

Signed-off-by: Andy Lutomirski <luto@amacapital.net>
Cc: Bandan Das <bsd@redhat.com>
Cc: stable@vger.kernel.org
Link: http://lkml.kernel.org/r/e2fa274e498c33988efac0ba8b7e3120f7f92d78.1413393027.git.luto@amacapital.net
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

2 files changed, 6 insertions, 3 deletions

diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
index 67760275544b..24b5894396a0 100644
--- a/arch/x86/kernel/apic/apic.c
+++ b/arch/x86/kernel/apic/apic.c
@@ -1297,7 +1297,7 @@ void setup_local_APIC(void)
         unsigned int value, queued;
         int i, j, acked = 0;
         unsigned long long tsc = 0, ntsc;
-        long long max_loops = cpu_khz;
+        long long max_loops = cpu_khz ? cpu_khz : 1000000;
 
         if (cpu_has_tsc)
                 rdtscll(tsc);
@@ -1383,7 +1383,7 @@ void setup_local_APIC(void)
                         break;
                 }
                 if (queued) {
-                        if (cpu_has_tsc) {
+                        if (cpu_has_tsc && cpu_khz) {
                                 rdtscll(ntsc);
                                 max_loops = (cpu_khz << 10) - (ntsc - tsc);
                         } else
diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index b6025f9e36c6..b7e50bba3bbb 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -1166,14 +1166,17 @@ void __init tsc_init(void)
 
         x86_init.timers.tsc_pre_init();
 
-        if (!cpu_has_tsc)
+        if (!cpu_has_tsc) {
+                setup_clear_cpu_cap(X86_FEATURE_TSC_DEADLINE_TIMER);
                 return;
+        }
 
         tsc_khz = x86_platform.calibrate_tsc();
         cpu_khz = tsc_khz;
 
         if (!tsc_khz) {
                 mark_tsc_unstable("could not calculate TSC khz");
+                setup_clear_cpu_cap(X86_FEATURE_TSC_DEADLINE_TIMER);
                 return;
         }