[PATCH kvm-unit-test 5/6] Add a simple kvmclock driver

Jason Wang
2010-08-27T05:49:49Z

Most of the codes were borrowed from arxh/x86/kernel/kvmclock.c. A
special bit: PV_CLOCK_CYCLE_RAW_TEST_BIT is used to notify the driver
to return unadjusted cycles.

Signed-off-by: Jason Wang <jasowang@redhat.com>
---
x86/kvmclock.c | 166 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
x86/kvmclock.h | 53 ++++++++++++++++++
2 files changed, 219 insertions(+), 0 deletions(-)
create mode 100644 x86/kvmclock.c
create mode 100644 x86/kvmclock.h

diff --git a/x86/kvmclock.c b/x86/kvmclock.c
new file mode 100644
index 0000000..6bfc858
--- /dev/null
+++ b/x86/kvmclock.c
@@ -0,0 +1,166 @@
+#include "libcflat.h"
+#include "smp.h"
+#include "atomic.h"
+#include "processor.h"
+#include "kvmclock.h"
+
+#define unlikely(x) __builtin_expect(!!(x), 0)
+
+struct pvclock_vcpu_time_info hv_clock[MAX_CPU];
+struct pvclock_wall_clock wall_clock;
+static unsigned char valid_flags = 0;
+static atomic64_t last_value = ATOMIC64_INIT(0);
+
+/*
+ * Scale a 64-bit delta by scaling and multiplying by a 32-bit fraction,
+ * yielding a 64-bit result.
+ */
+static inline u64 scale_delta(u64 delta, u32 mul_frac, int shift)
+{
+ u64 product;
+#ifdef __i386__
+ u32 tmp1, tmp2;
+#endif
+
+ if (shift < 0)
+ delta >>= -shift;
+ else
+ delta <<= shift;
+
+#ifdef __i386__
+ __asm__ (
+ "mul %5 ; "
+ "mov %4,%%eax ; "
+ "mov %%edx,%4 ; "
+ "mul %5 ; "
+ "xor %5,%5 ; "
+ "add %4,%%eax ; "
+ "adc %5,%%edx ; "
+ : "=A" (product), "=r" (tmp1), "=r" (tmp2)
+ : "a" ((u32)delta), "1" ((u32)(delta >> 32)), "2" (mul_frac) );
+#elif defined(__x86_64__)
+ __asm__ (
+ "mul %%rdx ; shrd $32,%%rdx,%%rax"
+ : "=a" (product) : "0" (delta), "d" ((u64)mul_frac) );
+#else
+#error implement me!
+#endif
+
+ return product;
+}
+
+static u64 pvclock_get_nsec_offset(struct pvclock_shadow_time *shadow)
+{
+ u64 delta = rdtsc() - shadow->tsc_timestamp;
+ return scale_delta(delta, shadow->tsc_to_nsec_mul, shadow->tsc_shift);
+}
+
+/*
+ * Reads a consistent set of time-base values from hypervisor,
+ * into a shadow data area.
+ */
+static unsigned pvclock_get_time_values(struct pvclock_shadow_time *dst,
+ struct pvclock_vcpu_time_info *src)
+{
+ do {
+ dst->version = src->version;
+ rmb(); /* fetch version before data */
+ dst->tsc_timestamp = src->tsc_timestamp;
+ dst->system_timestamp = src->system_time;
+ dst->tsc_to_nsec_mul = src->tsc_to_system_mul;
+ dst->tsc_shift = src->tsc_shift;
+ dst->flags = src->flags;
+ rmb(); /* test version after fetching data */
+ } while ((src->version & 1) || (dst->version != src->version));
+
+ return dst->version;
+}
+
+cycle_t pvclock_clocksource_read(struct pvclock_vcpu_time_info *src)
+{
+ struct pvclock_shadow_time shadow;
+ unsigned version;
+ cycle_t ret, offset;
+ u64 last;
+
+ do {
+ version = pvclock_get_time_values(&shadow, src);
+ barrier();
+ offset = pvclock_get_nsec_offset(&shadow);
+ ret = shadow.system_timestamp + offset;
+ barrier();
+ } while (version != src->version);
+
+ if ((valid_flags & PVCLOCK_RAW_CYCLE_BIT) ||
+ ((valid_flags & PVCLOCK_TSC_STABLE_BIT) &&
+ (shadow.flags & PVCLOCK_TSC_STABLE_BIT)))
+ return ret;
+
+ /*
+ * Assumption here is that last_value, a global accumulator, always goes
+ * forward. If we are less than that, we should not be much smaller.
+ * We assume there is an error marging we're inside, and then the correction
+ * does not sacrifice accuracy.
+ *
+ * For reads: global may have changed between test and return,
+ * but this means someone else updated poked the clock at a later time.
+ * We just need to make sure we are not seeing a backwards event.
+ *
+ * For updates: last_value = ret is not enough, since two vcpus could be
+ * updating at the same time, and one of them could be slightly behind,
+ * making the assumption that last_value always go forward fail to hold.
+ */
+ last = atomic64_read(&last_value);
+ do {
+ if (ret < last)
+ return last;
+ last = atomic64_cmpxchg(&last_value, last, ret);
+ } while (unlikely(last != ret));
+
+ return ret;
+}
+
+cycle_t kvm_clock_read()
+{
+ struct pvclock_vcpu_time_info *src;
+ cycle_t ret;
+ int index = smp_id();
+
+ src = &hv_clock[index];
+ ret = pvclock_clocksource_read(src);
+ return ret;
+}
+
+void kvm_clock_init(void *data)
+{
+ int index = smp_id();
+ struct pvclock_vcpu_time_info *hvc = &hv_clock[index];
+
+ printf("kvm-clock: cpu %d, msr 0x:%lx \n", index, hvc);
+ wrmsr(MSR_KVM_SYSTEM_TIME, (unsigned long)hvc | 1);
+}
+
+void kvm_clock_clear(void *data)
+{
+ wrmsr(MSR_KVM_SYSTEM_TIME, 0LL);
+}
+
+void kvm_get_wallclock(struct timespec *ts)
+{
+ u32 version;
+ wrmsr(MSR_KVM_WALL_CLOCK, (u64)&wall_clock);
+
+ do {
+ version = wall_clock.version;
+ rmb(); /* fetch version before time */
+ ts->sec = wall_clock.sec;
+ ts->nsec = wall_clock.nsec;
+ rmb(); /* fetch time before checking version */
+ } while ((wall_clock.version & 1) || (version != wall_clock.version));
+
+}
+
+void pvclock_set_flags(unsigned char flags)
+{
+ valid_flags = flags;
+}
diff --git a/x86/kvmclock.h b/x86/kvmclock.h
new file mode 100644
index 0000000..e3a1c02
--- /dev/null
+++ b/x86/kvmclock.h
@@ -0,0 +1,53 @@
+#ifndef KVMCLOCK_H
+#define KVMCLOCK_H
+
+#define MSR_KVM_WALL_CLOCK 0x11
+#define MSR_KVM_SYSTEM_TIME 0x12
+
+#define MAX_CPU 4
+
+#define PVCLOCK_TSC_STABLE_BIT (1 << 0)
+#define PVCLOCK_RAW_CYCLE_BIT (1 << 7) /* Get raw cycle */
+
+# define NSEC_PER_SEC 1000000000ULL
+
+typedef u64 cycle_t;
+
+struct pvclock_vcpu_time_info {
+ u32 version;
+ u32 pad0;
+ u64 tsc_timestamp;
+ u64 system_time;
+ u32 tsc_to_system_mul;
+ signed char tsc_shift;
+ u8 flags;
+ u8 pad[2];
+} __attribute__((__packed__)); /* 32 bytes */
+
+struct pvclock_wall_clock {
+ u32 version;
+ u32 sec;
+ u32 nsec;
+} __attribute__((__packed__));
+
+struct pvclock_shadow_time {
+ u64 tsc_timestamp; /* TSC at last update of time vals. */
+ u64 system_timestamp; /* Time, in nanosecs, since boot. */
+ u32 tsc_to_nsec_mul;
+ int tsc_shift;
+ u32 version;
+ u8 flags;
+};
+
+struct timespec {
+ u32 sec;
+ u32 nsec;
+};
+
+void pvclock_set_flags(unsigned char flags);
+cycle_t kvm_clock_read();
+void kvm_get_wallclock(struct timespec *ts);
+void kvm_clock_init(void *data);
+void kvm_clock_clear(void *data);
+
+#endif