Re: [PATCH v2 08/13] s390x: protvirt: Add new VCPU reset functions

[David Hildenbrand]

On 29.11.19 10:48, Janosch Frank wrote:
> CPU resets for protected guests need to be done via Ultravisor
> calls. Hence we need a way to issue these calls for each reset.
> 
> As we formerly had only one reset function and it was called for
> initial, as well as for the clear reset, we now need a new interface.
> 
> Signed-off-by: Janosch Frank <address@hidden>
> ---
>  target/s390x/cpu.c       | 14 ++++++++++++--
>  target/s390x/kvm-stub.c  | 10 +++++++++-
>  target/s390x/kvm.c       | 38 ++++++++++++++++++++++++++++++++------
>  target/s390x/kvm_s390x.h |  4 +++-
>  4 files changed, 56 insertions(+), 10 deletions(-)
> 
> diff --git a/target/s390x/cpu.c b/target/s390x/cpu.c
> index bd39cb54b7..52fefa1586 100644
> --- a/target/s390x/cpu.c
> +++ b/target/s390x/cpu.c
> @@ -131,8 +131,18 @@ static void s390_cpu_reset(CPUState *s, cpu_reset_type 
> type)
>      }
>  
>      /* Reset state inside the kernel that we cannot access yet from QEMU. */
> -    if (kvm_enabled() && type != S390_CPU_RESET_NORMAL) {
> -        kvm_s390_reset_vcpu(cpu);
> +    if (kvm_enabled()) {
> +        switch (type) {
> +        case S390_CPU_RESET_CLEAR:
> +            kvm_s390_reset_vcpu_clear(cpu);
> +            break;
> +        case S390_CPU_RESET_INITIAL:
> +            kvm_s390_reset_vcpu_initial(cpu);
> +            break;
> +        case S390_CPU_RESET_NORMAL:
> +            kvm_s390_reset_vcpu_normal(cpu);
> +            break;
> +        }

I would have assumed you only have to do that for pv? For ordinary
guests we can avoid unnecessary ioctls IMHO.

>      }
>  }
>  
> diff --git a/target/s390x/kvm-stub.c b/target/s390x/kvm-stub.c
> index 5152e2bdf1..c4cd497f85 100644
> --- a/target/s390x/kvm-stub.c
> +++ b/target/s390x/kvm-stub.c
> @@ -83,7 +83,15 @@ void kvm_s390_cmma_reset(void)
>  {
>  }
>  
> -void kvm_s390_reset_vcpu(S390CPU *cpu)
> +void kvm_s390_reset_vcpu_initial(S390CPU *cpu)
> +{
> +}
> +
> +void kvm_s390_reset_vcpu_clear(S390CPU *cpu)
> +{
> +}
> +
> +void kvm_s390_reset_vcpu_normal(S390CPU *cpu)
>  {
>  }
>  
> diff --git a/target/s390x/kvm.c b/target/s390x/kvm.c
> index b802d02ff5..5b1ed3acb4 100644
> --- a/target/s390x/kvm.c
> +++ b/target/s390x/kvm.c
> @@ -154,6 +154,7 @@ static int cap_ri;
>  static int cap_gs;
>  static int cap_hpage_1m;
>  static int cap_protvirt;
> +static int cap_vcpu_resets;
>  
>  static int active_cmma;
>  
> @@ -346,6 +347,7 @@ int kvm_arch_init(MachineState *ms, KVMState *s)
>      cap_mem_op = kvm_check_extension(s, KVM_CAP_S390_MEM_OP);
>      cap_s390_irq = kvm_check_extension(s, KVM_CAP_S390_INJECT_IRQ);
>      cap_protvirt = kvm_check_extension(s, KVM_CAP_S390_PROTECTED);
> +    cap_vcpu_resets = kvm_check_extension(s, KVM_CAP_S390_VCPU_RESETS);
>  
>      if (!kvm_check_extension(s, KVM_CAP_S390_GMAP)
>          || !kvm_check_extension(s, KVM_CAP_S390_COW)) {
> @@ -407,20 +409,44 @@ int kvm_arch_destroy_vcpu(CPUState *cs)
>      return 0;
>  }
>  
> -void kvm_s390_reset_vcpu(S390CPU *cpu)
> +static void kvm_s390_reset_vcpu(S390CPU *cpu, unsigned long type)
>  {
>      CPUState *cs = CPU(cpu);
>  
> -    /* The initial reset call is needed here to reset in-kernel
> -     * vcpu data that we can't access directly from QEMU
> -     * (i.e. with older kernels which don't support sync_regs/ONE_REG).
> -     * Before this ioctl cpu_synchronize_state() is called in common kvm
> -     * code (kvm-all) */
> +    /*
> +     * The reset call is needed here to reset in-kernel vcpu data that
> +     * we can't access directly from QEMU (i.e. with older kernels
> +     * which don't support sync_regs/ONE_REG).  Before this ioctl
> +     * cpu_synchronize_state() is called in common kvm code
> +     * (kvm-all).
> +     */
> +    if (cap_vcpu_resets) {
> +        if (kvm_vcpu_ioctl(cs, KVM_S390_VCPU_RESET, type)) {
> +            error_report("CPU reset type %ld failed on CPU %i",
> +                         type, cs->cpu_index);
> +        }
> +        return;> +    }

This is broken for S390_CPU_RESET_NORMAL where we don't do a
KVM_S390_INITIAL_RESET for !pv ...

Can't we limit that new handling to pv only and keep it out of this path?


[...]


-- 
Thanks,

David / dhildenb