[PATCH] i386: Handle 32 bit PerfMon Counter writes cleanly in i386 nmi_watchdog

Change i386 nmi handler to handle 32 bit perfmon counter MSR writes cleanly.

Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
Signed-off-by: Andi Kleen <ak@suse.de>

1 files changed, 48 insertions, 16 deletions

diff --git a/arch/i386/kernel/nmi.c b/arch/i386/kernel/nmi.c
index 1a6f8bb8881c..7d3f4e22d6fb 100644
--- a/arch/i386/kernel/nmi.c
+++ b/arch/i386/kernel/nmi.c
@@ -216,6 +216,28 @@ static __init void nmi_cpu_busy(void *data)
 }
 #endif
 
+static unsigned int adjust_for_32bit_ctr(unsigned int hz)
+{
+        u64 counter_val;
+        unsigned int retval = hz;
+
+        /*
+         * On Intel CPUs with P6/ARCH_PERFMON only 32 bits in the counter
+         * are writable, with higher bits sign extending from bit 31.
+         * So, we can only program the counter with 31 bit values and
+         * 32nd bit should be 1, for 33.. to be 1.
+         * Find the appropriate nmi_hz
+         */
+        counter_val = (u64)cpu_khz * 1000;
+        do_div(counter_val, retval);
+        if (counter_val > 0x7fffffffULL) {
+                u64 count = (u64)cpu_khz * 1000;
+                do_div(count, 0x7fffffffUL);
+                retval = count + 1;
+        }
+        return retval;
+}
+
 static int __init check_nmi_watchdog(void)
 {
         unsigned int *prev_nmi_count;
@@ -281,18 +303,10 @@ static int __init check_nmi_watchdog(void)
                 struct nmi_watchdog_ctlblk *wd = &__get_cpu_var(nmi_watchdog_ctlblk);
 
                 nmi_hz = 1;
-                /*
-                 * On Intel CPUs with ARCH_PERFMON only 32 bits in the counter
-                 * are writable, with higher bits sign extending from bit 31.
-                 * So, we can only program the counter with 31 bit values and
-                 * 32nd bit should be 1, for 33.. to be 1.
-                 * Find the appropriate nmi_hz
-                 */
-                if (wd->perfctr_msr == MSR_ARCH_PERFMON_PERFCTR0 &&
-                        ((u64)cpu_khz * 1000) > 0x7fffffffULL) {
-                        u64 count = (u64)cpu_khz * 1000;
-                        do_div(count, 0x7fffffffUL);
-                        nmi_hz = count + 1;
+
+                if (wd->perfctr_msr == MSR_P6_PERFCTR0 ||
+                    wd->perfctr_msr == MSR_ARCH_PERFMON_PERFCTR0) {
+                        nmi_hz = adjust_for_32bit_ctr(nmi_hz);
                 }
         }
 
@@ -442,6 +456,17 @@ static void write_watchdog_counter(unsigned int perfctr_msr, const char *descr)
         wrmsrl(perfctr_msr, 0 - count);
 }
 
+static void write_watchdog_counter32(unsigned int perfctr_msr,
+                const char *descr)
+{
+        u64 count = (u64)cpu_khz * 1000;
+
+        do_div(count, nmi_hz);
+        if(descr)
+                Dprintk("setting %s to -0x%08Lx\n", descr, count);
+        wrmsr(perfctr_msr, (u32)(-count), 0);
+}
+
 /* Note that these events don't tick when the CPU idles. This means
    the frequency varies with CPU load. */
 
@@ -531,7 +556,8 @@ static int setup_p6_watchdog(void)
 
         /* setup the timer */
         wrmsr(evntsel_msr, evntsel, 0);
-        write_watchdog_counter(perfctr_msr, "P6_PERFCTR0");
+        nmi_hz = adjust_for_32bit_ctr(nmi_hz);
+        write_watchdog_counter32(perfctr_msr, "P6_PERFCTR0");
         apic_write(APIC_LVTPC, APIC_DM_NMI);
         evntsel |= P6_EVNTSEL0_ENABLE;
         wrmsr(evntsel_msr, evntsel, 0);
@@ -704,7 +730,8 @@ static int setup_intel_arch_watchdog(void)
 
         /* setup the timer */
         wrmsr(evntsel_msr, evntsel, 0);
-        write_watchdog_counter(perfctr_msr, "INTEL_ARCH_PERFCTR0");
+        nmi_hz = adjust_for_32bit_ctr(nmi_hz);
+        write_watchdog_counter32(perfctr_msr, "INTEL_ARCH_PERFCTR0");
         apic_write(APIC_LVTPC, APIC_DM_NMI);
         evntsel |= ARCH_PERFMON_EVENTSEL0_ENABLE;
         wrmsr(evntsel_msr, evntsel, 0);
@@ -956,6 +983,8 @@ __kprobes int nmi_watchdog_tick(struct pt_regs * regs, unsigned reason)
                                 dummy &= ~P4_CCCR_OVF;
                                 wrmsrl(wd->cccr_msr, dummy);
                                 apic_write(APIC_LVTPC, APIC_DM_NMI);
+                                /* start the cycle over again */
+                                write_watchdog_counter(wd->perfctr_msr, NULL);
                         }
                         else if (wd->perfctr_msr == MSR_P6_PERFCTR0 ||
                                  wd->perfctr_msr == MSR_ARCH_PERFMON_PERFCTR0) {
@@ -964,9 +993,12 @@ __kprobes int nmi_watchdog_tick(struct pt_regs * regs, unsigned reason)
                                  * other P6 variant.
                                  * ArchPerfom/Core Duo also needs this */
                                 apic_write(APIC_LVTPC, APIC_DM_NMI);
+                                /* P6/ARCH_PERFMON has 32 bit counter write */
+                                write_watchdog_counter32(wd->perfctr_msr, NULL);
+                        } else {
+                                /* start the cycle over again */
+                                write_watchdog_counter(wd->perfctr_msr, NULL);
                         }
-                        /* start the cycle over again */
-                        write_watchdog_counter(wd->perfctr_msr, NULL);
                         rc = 1;
                 } else if (nmi_watchdog == NMI_IO_APIC) {
                         /* don't know how to accurately check for this.