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kvmclock: Ensure time in migration never goes backward

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When we migrate we ask the kernel about its current belief on what the guest
time would be. However, I've seen cases where the kvmclock guest structure
indicates a time more recent than the kvm returned time.

To make sure we never go backwards, calculate what the guest would have seen
as time at the point of migration and use that value instead of the kernel
returned one when it's more recent.  This bases the view of the kvmclock
after migration on the same foundation in host as well as guest.

Signed-off-by: Alexander Graf <agraf@suse.de>
Cc: qemu-stable@nongnu.org
Reviewed-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Alexander Graf 2014-05-16 17:15:21 +02:00 committed by Paolo Bonzini
parent 1a381811b4
commit a096b3a673
1 changed files with 48 additions and 0 deletions
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48
hw/i386/kvm/clock.c
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@ -14,6 +14,7 @@
*/ */
#include "qemu-common.h" #include "qemu-common.h"
#include "qemu/host-utils.h"
#include "sysemu/sysemu.h" #include "sysemu/sysemu.h"
#include "sysemu/kvm.h" #include "sysemu/kvm.h"
#include "hw/sysbus.h" #include "hw/sysbus.h"
@ -34,6 +35,47 @@ typedef struct KVMClockState {
bool clock_valid; bool clock_valid;
} KVMClockState; } KVMClockState;
struct pvclock_vcpu_time_info {
uint32_t version;
uint32_t pad0;
uint64_t tsc_timestamp;
uint64_t system_time;
uint32_t tsc_to_system_mul;
int8_t tsc_shift;
uint8_t flags;
uint8_t pad[2];
} __attribute__((__packed__)); /* 32 bytes */
static uint64_t kvmclock_current_nsec(KVMClockState *s)
{
CPUState *cpu = first_cpu;
CPUX86State *env = cpu->env_ptr;
hwaddr kvmclock_struct_pa = env->system_time_msr & ~1ULL;
uint64_t migration_tsc = env->tsc;
struct pvclock_vcpu_time_info time;
uint64_t delta;
uint64_t nsec_lo;
uint64_t nsec_hi;
uint64_t nsec;
if (!(env->system_time_msr & 1ULL)) {
/* KVM clock not active */
return 0;
}
cpu_physical_memory_read(kvmclock_struct_pa, &time, sizeof(time));
delta = migration_tsc - time.tsc_timestamp;
if (time.tsc_shift < 0) {
delta >>= -time.tsc_shift;
} else {
delta <<= time.tsc_shift;
}
mulu64(&nsec_lo, &nsec_hi, delta, time.tsc_to_system_mul);
nsec = (nsec_lo >> 32) | (nsec_hi << 32);
return nsec + time.system_time;
}
static void kvmclock_vm_state_change(void *opaque, int running, static void kvmclock_vm_state_change(void *opaque, int running,
RunState state) RunState state)
@ -45,9 +87,15 @@ static void kvmclock_vm_state_change(void *opaque, int running,
if (running) { if (running) {
struct kvm_clock_data data; struct kvm_clock_data data;
uint64_t time_at_migration = kvmclock_current_nsec(s);
s->clock_valid = false; s->clock_valid = false;
/* We can't rely on the migrated clock value, just discard it */
if (time_at_migration) {
s->clock = time_at_migration;
}
data.clock = s->clock; data.clock = s->clock;
data.flags = 0; data.flags = 0;
ret = kvm_vm_ioctl(kvm_state, KVM_SET_CLOCK, &data); ret = kvm_vm_ioctl(kvm_state, KVM_SET_CLOCK, &data);