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Subject[PATCH 3.10 110/123] x86, apic: Handle a bad TSC more gracefully
Date
3.10-stable review patch.  If anyone has any objections, please let me know.

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

From: Andy Lutomirski <luto@amacapital.net>

commit b47dcbdc5161d3d5756f430191e2840d9b855492 upstream.

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>
Link: http://lkml.kernel.org/r/e2fa274e498c33988efac0ba8b7e3120f7f92d78.1413393027.git.luto@amacapital.net
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
arch/x86/kernel/apic/apic.c | 4 ++--
arch/x86/kernel/tsc.c | 5 ++++-
2 files changed, 6 insertions(+), 3 deletions(-)

--- a/arch/x86/kernel/apic/apic.c
+++ b/arch/x86/kernel/apic/apic.c
@@ -1263,7 +1263,7 @@ void __cpuinit 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);
@@ -1360,7 +1360,7 @@ void __cpuinit 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
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -968,14 +968,17 @@ 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;
}




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