Re: [Qemu-devel] [PATCH 1/2 v3] [S390-KVM] Regsync: Allow selective runtime register synchronization

[Christian Borntraeger <borntraeger@de.ibm.com>]

On 11/03/13 18:58, Jason J. Herne wrote:
> We want to avoid expensive register synchronization IOCTL's on the hot path so
> a new kvm_s390_get_registers_partial() is introduced as a compliment to
> kvm_arch_get_registers().  The new function is called on the hot path, and
> kvm_arch_get_registers() is called when we need the complete runtime register
> state.
> 
> kvm_arch_put_registers() is updated to only sync the partial runtime set when
> we've only dirtied the partial runtime set.  This is to avoid sending bad data
> back to KVM if we've only partially synced the runtime register set.
> 
> Signed-off-by: Jason J. Herne <jjherne@us.ibm.com>
> Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com>

Alex,

we have this code in our private tree (the one thats used by the testers) for a while
now and it seems to work fine. 
This should be ok to apply. 
Since this also fixes the problem that s390 has not a complete view of the kvm registers
in places were we want it (dump etc) we might even consider this a bugfix.

Your take if this is still good for 1.5.

Christian




> ---
>  target-s390x/cpu.h |   17 +++++++++++++
>  target-s390x/kvm.c |   67 ++++++++++++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 84 insertions(+)
> 
> diff --git a/target-s390x/cpu.h b/target-s390x/cpu.h
> index 9cb739d..69ecb05 100644
> --- a/target-s390x/cpu.h
> +++ b/target-s390x/cpu.h
> @@ -78,6 +78,11 @@ typedef struct MchkQueue {
>      uint16_t type;
>  } MchkQueue;
> 
> +/* Defined values for CPUS390XState.runtime_reg_dirty_mask */
> +#define KVM_S390_RUNTIME_DIRTY_NONE     0
> +#define KVM_S390_RUNTIME_DIRTY_PARTIAL  1
> +#define KVM_S390_RUNTIME_DIRTY_FULL     2
> +
>  typedef struct CPUS390XState {
>      uint64_t regs[16];     /* GP registers */
>      CPU_DoubleU fregs[16]; /* FP registers */
> @@ -121,6 +126,13 @@ typedef struct CPUS390XState {
>      uint64_t cputm;
>      uint32_t todpr;
> 
> +    /* on S390 the runtime register set has two dirty states:
> +     * a partial dirty state in which only the registers that
> +     * are needed all the time are fetched. And a fully dirty
> +     * state in which all runtime registers are fetched.
> +     */
> +    uint32_t runtime_reg_dirty_mask;
> +
>      CPU_COMMON
> 
>      /* reset does memset(0) up to here */
> @@ -1068,6 +1080,7 @@ void kvm_s390_io_interrupt(S390CPU *cpu, uint16_t subchannel_id,
>                             uint32_t io_int_word);
>  void kvm_s390_crw_mchk(S390CPU *cpu);
>  void kvm_s390_enable_css_support(S390CPU *cpu);
> +int kvm_s390_get_registers_partial(CPUState *cpu);
>  #else
>  static inline void kvm_s390_io_interrupt(S390CPU *cpu,
>                                          uint16_t subchannel_id,
> @@ -1082,6 +1095,10 @@ static inline void kvm_s390_crw_mchk(S390CPU *cpu)
>  static inline void kvm_s390_enable_css_support(S390CPU *cpu)
>  {
>  }
> +static inline int kvm_s390_get_registers_partial(CPUState *cpu)
> +{
> +    return -ENOSYS;
> +}
>  #endif
> 
>  static inline void s390_io_interrupt(S390CPU *cpu,
> diff --git a/target-s390x/kvm.c b/target-s390x/kvm.c
> index 8f111ae..934757e 100644
> --- a/target-s390x/kvm.c
> +++ b/target-s390x/kvm.c
> @@ -123,6 +123,7 @@ int kvm_arch_put_registers(CPUState *cs, int level)
>  {
>      S390CPU *cpu = S390_CPU(cs);
>      CPUS390XState *env = &cpu->env;
> +    struct kvm_one_reg reg;
>      struct kvm_sregs sregs;
>      struct kvm_regs regs;
>      int ret;
> @@ -147,6 +148,30 @@ int kvm_arch_put_registers(CPUState *cs, int level)
>          }
>      }
> 
> +    if (env->runtime_reg_dirty_mask == KVM_S390_RUNTIME_DIRTY_FULL) {
> +        reg.id = KVM_REG_S390_CPU_TIMER;
> +        reg.addr = (__u64)&(env->cputm);
> +        ret = kvm_vcpu_ioctl(cs, KVM_SET_ONE_REG, &reg);
> +        if (ret < 0) {
> +            return ret;
> +        }
> +
> +        reg.id = KVM_REG_S390_CLOCK_COMP;
> +        reg.addr = (__u64)&(env->ckc);
> +        ret = kvm_vcpu_ioctl(cs, KVM_SET_ONE_REG, &reg);
> +        if (ret < 0) {
> +            return ret;
> +        }
> +
> +        reg.id = KVM_REG_S390_TODPR;
> +        reg.addr = (__u64)&(env->todpr);
> +        ret = kvm_vcpu_ioctl(cs, KVM_SET_ONE_REG, &reg);
> +        if (ret < 0) {
> +            return ret;
> +        }
> +    }
> +    env->runtime_reg_dirty_mask = KVM_S390_RUNTIME_DIRTY_NONE;
> +
>      /* Do we need to save more than that? */
>      if (level == KVM_PUT_RUNTIME_STATE) {
>          return 0;
> @@ -186,11 +211,52 @@ int kvm_arch_get_registers(CPUState *cs)
>  {
>      S390CPU *cpu = S390_CPU(cs);
>      CPUS390XState *env = &cpu->env;
> +    struct kvm_one_reg reg;
> +    int r;
> +
> +    r = kvm_s390_get_registers_partial(cs);
> +    if (r < 0) {
> +        return r;
> +    }
> +
> +    reg.id = KVM_REG_S390_CPU_TIMER;
> +    reg.addr = (__u64)&(env->cputm);
> +    r = kvm_vcpu_ioctl(cs, KVM_GET_ONE_REG, &reg);
> +    if (r < 0) {
> +        return r;
> +    }
> +
> +    reg.id = KVM_REG_S390_CLOCK_COMP;
> +    reg.addr = (__u64)&(env->ckc);
> +    r = kvm_vcpu_ioctl(cs, KVM_GET_ONE_REG, &reg);
> +    if (r < 0) {
> +        return r;
> +    }
> +
> +    reg.id = KVM_REG_S390_TODPR;
> +    reg.addr = (__u64)&(env->todpr);
> +    r = kvm_vcpu_ioctl(cs, KVM_GET_ONE_REG, &reg);
> +    if (r < 0) {
> +        return r;
> +    }
> +
> +    env->runtime_reg_dirty_mask = KVM_S390_RUNTIME_DIRTY_FULL;
> +    return 0;
> +}
> +
> +int kvm_s390_get_registers_partial(CPUState *cs)
> +{
> +    S390CPU *cpu = S390_CPU(cs);
> +    CPUS390XState *env = &cpu->env;
>      struct kvm_sregs sregs;
>      struct kvm_regs regs;
>      int ret;
>      int i;
> 
> +    if (env->runtime_reg_dirty_mask) {
> +        return 0;
> +    }
> +
>      /* get the PSW */
>      env->psw.addr = cs->kvm_run->psw_addr;
>      env->psw.mask = cs->kvm_run->psw_mask;
> @@ -236,6 +302,7 @@ int kvm_arch_get_registers(CPUState *cs)
>          /* no prefix without sync regs */
>      }
> 
> +    env->runtime_reg_dirty_mask = KVM_S390_RUNTIME_DIRTY_PARTIAL;
>      return 0;
>  }
>