From 796cbf543aacc6a7f9eeeb71b4cda01452267c00 Mon Sep 17 00:00:00 2001 From: Marcelo Tosatti Date: Mon, 22 Sep 2014 17:05:27 +0200 Subject: [PATCH 08/13] kvmclock: Ensure time in migration never goes backward Message-id: <20140922170613.897959809@redhat.com> Patchwork-id: 61360 O-Subject: [PATCH RHEV-7.1 qemu-kvm-rhev 3/3] kvmclock: Ensure time in migration never goes backward Bugzilla: 1143054 RH-Acked-by: Eduardo Habkost RH-Acked-by: Radim Krcmar RH-Acked-by: Paolo Bonzini commit 9a48bcd1b82494671c111109b0eefdb882581499 upstream of qemu-kvm.git uq/master branch Author: Alexander Graf 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 Cc: qemu-stable@nongnu.org Reviewed-by: Marcelo Tosatti Signed-off-by: Paolo Bonzini Signed-off-by: Miroslav Rezanina --- hw/i386/kvm/clock.c | 49 +++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 49 insertions(+) diff --git a/hw/i386/kvm/clock.c b/hw/i386/kvm/clock.c index 9d65766..1ac60d6 100644 --- a/hw/i386/kvm/clock.c +++ b/hw/i386/kvm/clock.c @@ -14,6 +14,7 @@ */ #include "qemu-common.h" +#include "qemu/host-utils.h" #include "sysemu/sysemu.h" #include "sysemu/kvm.h" #include "sysemu/cpus.h" @@ -35,6 +36,48 @@ typedef struct KVMClockState { bool clock_valid; } 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)); + + assert(time.tsc_timestamp <= migration_tsc); + 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, RunState state) @@ -46,9 +89,15 @@ static void kvmclock_vm_state_change(void *opaque, int running, if (running) { struct kvm_clock_data data; + uint64_t time_at_migration = kvmclock_current_nsec(s); 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.flags = 0; ret = kvm_vm_ioctl(kvm_state, KVM_SET_CLOCK, &data); -- 1.8.3.1