[PATCH v2 16/21] KVM: x86: Restrict writeback of VCPU state

Jan Kiszka
2010-02-03T08:54:21Z

Do not write nmi_pending, sipi_vector, and mpstate unless we at least go
through a reset. And TSC as well as KVM wallclocks should only be
written on full sync, otherwise we risk to drop some time on during
state read-modify-write.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
---
kvm.h | 2 +-
qemu-kvm-x86.c | 2 +-
target-i386/kvm.c | 32 ++++++++++++++++++++------------
target-i386/machine.c | 2 +-
4 files changed, 23 insertions(+), 15 deletions(-)

diff --git a/kvm.h b/kvm.h
index ee8b3f6..e4005d8 100644
--- a/kvm.h
+++ b/kvm.h
@@ -53,7 +53,7 @@ int kvm_set_migration_log(int enable);

int kvm_has_sync_mmu(void);
int kvm_has_vcpu_events(void);
-int kvm_put_vcpu_events(CPUState *env);
+int kvm_put_vcpu_events(CPUState *env, int level);
int kvm_get_vcpu_events(CPUState *env);

void kvm_setup_guest_memory(void *start, size_t size);
diff --git a/qemu-kvm-x86.c b/qemu-kvm-x86.c
index c6cf317..0d2cce8 100644
--- a/qemu-kvm-x86.c
+++ b/qemu-kvm-x86.c
@@ -1398,7 +1398,7 @@ void kvm_arch_push_nmi(void *opaque)
void kvm_arch_cpu_reset(CPUState *env)
{
kvm_arch_reset_vcpu(env);
- kvm_put_vcpu_events(env);
+ kvm_put_vcpu_events(env, KVM_PUT_RESET_STATE);
kvm_reset_mpstate(env);
if (!cpu_is_bsp(env) && !kvm_irqchip_in_kernel()) {
env->interrupt_request &= ~CPU_INTERRUPT_HARD;
diff --git a/target-i386/kvm.c b/target-i386/kvm.c
index 4a0c8bb..fefd5a5 100644
--- a/target-i386/kvm.c
+++ b/target-i386/kvm.c
@@ -544,7 +544,7 @@ static void kvm_msr_entry_set(struct kvm_msr_entry *entry,
entry->data = value;
}

-static int kvm_put_msrs(CPUState *env)
+static int kvm_put_msrs(CPUState *env, int level)
{
struct {
struct kvm_msrs info;
@@ -558,7 +558,6 @@ static int kvm_put_msrs(CPUState *env)
kvm_msr_entry_set(&msrs[n++], MSR_IA32_SYSENTER_EIP, env->sysenter_eip);
if (kvm_has_msr_star(env))
kvm_msr_entry_set(&msrs[n++], MSR_STAR, env->star);
- kvm_msr_entry_set(&msrs[n++], MSR_IA32_TSC, env->tsc);
kvm_msr_entry_set(&msrs[n++], MSR_VM_HSAVE_PA, env->vm_hsave);
#ifdef TARGET_X86_64
/* FIXME if lm capable */
@@ -567,8 +566,12 @@ static int kvm_put_msrs(CPUState *env)
kvm_msr_entry_set(&msrs[n++], MSR_FMASK, env->fmask);
kvm_msr_entry_set(&msrs[n++], MSR_LSTAR, env->lstar);
#endif
- kvm_msr_entry_set(&msrs[n++], MSR_KVM_SYSTEM_TIME, env->system_time_msr);
- kvm_msr_entry_set(&msrs[n++], MSR_KVM_WALL_CLOCK, env->wall_clock_msr);
+ if (level == KVM_PUT_FULL_STATE) {
+ kvm_msr_entry_set(&msrs[n++], MSR_IA32_TSC, env->tsc);
+ kvm_msr_entry_set(&msrs[n++], MSR_KVM_SYSTEM_TIME,
+ env->system_time_msr);
+ kvm_msr_entry_set(&msrs[n++], MSR_KVM_WALL_CLOCK, env->wall_clock_msr);
+ }

msr_data.info.nmsrs = n;

@@ -786,7 +789,7 @@ static int kvm_get_mp_state(CPUState *env)
}
#endif

-int kvm_put_vcpu_events(CPUState *env)
+int kvm_put_vcpu_events(CPUState *env, int level)
{
#ifdef KVM_CAP_VCPU_EVENTS
struct kvm_vcpu_events events;
@@ -810,8 +813,11 @@ int kvm_put_vcpu_events(CPUState *env)

events.sipi_vector = env->sipi_vector;

- events.flags =
- KVM_VCPUEVENT_VALID_NMI_PENDING | KVM_VCPUEVENT_VALID_SIPI_VECTOR;
+ events.flags = 0;
+ if (level >= KVM_PUT_RESET_STATE) {
+ events.flags |=
+ KVM_VCPUEVENT_VALID_NMI_PENDING | KVM_VCPUEVENT_VALID_SIPI_VECTOR;
+ }

return kvm_vcpu_ioctl(env, KVM_SET_VCPU_EVENTS, &events);
#else
@@ -882,15 +888,17 @@ int kvm_arch_put_registers(CPUState *env, int level)
if (ret < 0)
return ret;

- ret = kvm_put_msrs(env);
+ ret = kvm_put_msrs(env, level);
if (ret < 0)
return ret;

- ret = kvm_put_mp_state(env);
- if (ret < 0)
- return ret;
+ if (level >= KVM_PUT_RESET_STATE) {
+ ret = kvm_put_mp_state(env);
+ if (ret < 0)
+ return ret;
+ }

- ret = kvm_put_vcpu_events(env);
+ ret = kvm_put_vcpu_events(env, level);
if (ret < 0)
return ret;

diff --git a/target-i386/machine.c b/target-i386/machine.c
index 61e6a87..6fca559 100644
--- a/target-i386/machine.c
+++ b/target-i386/machine.c
@@ -362,7 +362,7 @@ static int cpu_post_load(void *opaque, int version_id)

if (kvm_enabled()) {
kvm_load_tsc(env);
- kvm_put_vcpu_events(env);
+ kvm_put_vcpu_events(env, KVM_PUT_FULL_STATE);
}

return 0;
--
1.6.0.2