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    Subject[PATCH 3.17 275/319] x86, apic: Handle a bad TSC more gracefully
    Date
    3.17-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
    @@ -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
    --- 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;
    }




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