On 2011-02-17 17:35, Marcelo Tosatti wrote:
> On Tue, Feb 15, 2011 at 09:23:32AM +0100, Jan Kiszka wrote:
>> The current way of injecting MCE events without updating of and
>> synchronizing with the CPUState is broken and causes spurious
>> corruptions of the MCE-related parts of the CPUState.
>
> Can you explain how? The current pronlem with MCE is that it bypasses
> writeback code, but corruption has nothing to do with that.
It's precisely the same scenario as with the old debug exception
re-injection: If we update the pending exception state via
KVM_SET_VCPU_EVENTS, we must not inject it via any other path. Otherwise
we end up with overwritten/lost events - which is extremely critical for
this rarely taken code paths.
Jut like parts of KVM_SET_GUEST_DEBUG, KVM_X86_SET_MCE pre-dates
KVM_SET_VCPU_EVENTS which obsoleted all other exception injection
mechanisms.
>
>> As a first step towards a fix, enhance the state writeback code with
>> support for injecting events that are pending in the CPUState. A pending
>> exception will then be signaled via cpu_interrupt(CPU_INTERRUPT_MCE).
>> And, just like for TCG, we need to leave the halt state when
>> CPU_INTERRUPT_MCE is pending (left broken for the to-be-removed old KVM
>> code).
>>
>> This will also allow to unify TCG and KVM injection code.
>>
>> Signed-off-by: Jan Kiszka <jan.kiszka@xxxxxxxxxxx>
>> CC: Huang Ying <ying.huang@xxxxxxxxx>
>> CC: Hidetoshi Seto <seto.hidetoshi@xxxxxxxxxxxxxx>
>> CC: Jin Dongming <jin.dongming@xxxxxxxxxxxxxxxxxx>
>> ---
>> target-i386/kvm.c | 75 +++++++++++++++++++++++++++++++++++++++++++++++++---
>> 1 files changed, 70 insertions(+), 5 deletions(-)
>>
>> diff --git a/target-i386/kvm.c b/target-i386/kvm.c
>> index f909661..46f45db 100644
>> --- a/target-i386/kvm.c
>> +++ b/target-i386/kvm.c
>> @@ -467,6 +467,44 @@ void kvm_inject_x86_mce(CPUState *cenv, int bank, uint64_t status,
>> #endif /* !KVM_CAP_MCE*/
>> }
>>
>> +static int kvm_inject_mce_oldstyle(CPUState *env)
>> +{
>> +#ifdef KVM_CAP_MCE
>> + if (kvm_has_vcpu_events()) {
>> + return 0;
>> + }
>> + if (env->interrupt_request & CPU_INTERRUPT_MCE) {
>> + unsigned int bank, bank_num = env->mcg_cap & 0xff;
>> + struct kvm_x86_mce mce;
>> +
>> + /* We must not raise CPU_INTERRUPT_MCE if it's not supported. */
>> + assert(env->mcg_cap);
>> +
>> + env->interrupt_request &= ~CPU_INTERRUPT_MCE;
>> +
>> + /*
>> + * There must be at least one bank in use if CPU_INTERRUPT_MCE was set.
>> + * Find it and use its values for the event injection.
>> + */
>> + for (bank = 0; bank < bank_num; bank++) {
>> + if (env->mce_banks[bank * 4 + 1] & MCI_STATUS_VAL) {
>> + break;
>> + }
>> + }
>> + assert(bank < bank_num);
>> +
>> + mce.bank = bank;
>> + mce.status = env->mce_banks[bank * 4 + 1];
>> + mce.mcg_status = env->mcg_status;
>> + mce.addr = env->mce_banks[bank * 4 + 2];
>> + mce.misc = env->mce_banks[bank * 4 + 3];
>> +
>> + return kvm_vcpu_ioctl(env, KVM_X86_SET_MCE, &mce);
>> + }
>> +#endif /* KVM_CAP_MCE */
>> + return 0;
>> +}
>> +
>> static void cpu_update_state(void *opaque, int running, int reason)
>> {
>> CPUState *env = opaque;
>> @@ -1375,10 +1413,25 @@ static int kvm_put_vcpu_events(CPUState *env, int level)
>> return 0;
>> }
>>
>> - events.exception.injected = (env->exception_injected >= 0);
>> - events.exception.nr = env->exception_injected;
>> - events.exception.has_error_code = env->has_error_code;
>> - events.exception.error_code = env->error_code;
>> + if (env->interrupt_request & CPU_INTERRUPT_MCE) {
>> + /* We must not raise CPU_INTERRUPT_MCE if it's not supported. */
>> + assert(env->mcg_cap);
>> +
>> + env->interrupt_request &= ~CPU_INTERRUPT_MCE;
>> + if (env->exception_injected == EXCP08_DBLE) {
>> + /* this means triple fault */
>> + qemu_system_reset_request();
>> + env->exit_request = 1;
>> + }
>> + events.exception.injected = 1;
>> + events.exception.nr = EXCP12_MCHK;
>> + events.exception.has_error_code = 0;
>> + } else {
>> + events.exception.injected = (env->exception_injected >= 0);
>> + events.exception.nr = env->exception_injected;
>> + events.exception.has_error_code = env->has_error_code;
>> + events.exception.error_code = env->error_code;
>> + }
>
> IMO it is important to maintain a scope for kvm_put_vcpu_events /
> kvm_get_vcpu_events: they synchronize state to/from the kernel. Not more
> than that. Whatever you're trying to do here should be higher in the
> vcpu loop code.
We pick up CPU_INTERRUPT_MCE and translate it into the right exception
that put_vcpu_events is about to sync to the kernel. What should be done
earlier of those steps? Calculating env->exception_injected?
>
>> events.interrupt.injected = (env->interrupt_injected >= 0);
>> events.interrupt.nr = env->interrupt_injected;
>> @@ -1539,6 +1592,11 @@ int kvm_arch_put_registers(CPUState *env, int level)
>> if (ret < 0) {
>> return ret;
>> }
>> + /* must be before kvm_put_msrs */
>> + ret = kvm_inject_mce_oldstyle(env);
>> + if (ret < 0) {
>> + return ret;
>> + }
>> ret = kvm_put_msrs(env, level);
>> if (ret < 0) {
>> return ret;
>> @@ -1678,10 +1736,17 @@ void kvm_arch_post_run(CPUState *env, struct kvm_run *run)
>> int kvm_arch_process_irqchip_events(CPUState *env)
>> {
>> if (kvm_irqchip_in_kernel()) {
>> + if (env->interrupt_request & CPU_INTERRUPT_MCE) {
>> + kvm_cpu_synchronize_state(env);
>> + if (env->mp_state == KVM_MP_STATE_HALTED) {
>> + env->mp_state = KVM_MP_STATE_RUNNABLE;
>> + }
>> + }
>
> Should not manipulate mp_state of a running vcpu (should only do that
> for migration when vcpu is stopped), since its managed by the kernel,
> for irqchip case.
Not for asynchronously injected MCEs. The target CPU would simply
oversleep them. MCEs are not in the scope of the in-kernel irqchip.
Jan
--
Siemens AG, Corporate Technology, CT T DE IT 1
Corporate Competence Center Embedded Linux
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