Re: [Qemu-devel] [PATCH v2 01/14] target/arm/cpu64: Ensure kvm really supports aarch64=off

[Auger Eric <eric.auger@redhat.com>]

Hi Drew,

On 6/25/19 3:34 PM, Andrew Jones wrote:
> On Tue, Jun 25, 2019 at 11:35:12AM +0200, Auger Eric wrote:
>> Hi Drew,
>>
>> On 6/21/19 6:34 PM, Andrew Jones wrote:
>>> If -cpu <cpu>,aarch64=off is used then KVM must also be used, and it
>>> and the host must support running the vcpu in 32-bit mode. Also, if
s/and it//
>>> -cpu <cpu>,aarch64=on is used, then it doesn't matter if kvm is
>>> enabled or not.
>>>
>>> Signed-off-by: Andrew Jones <drjones@redhat.com>
>>
>>
>>> ---
>>>  target/arm/cpu64.c   | 12 ++++++------
>>>  target/arm/kvm64.c   | 11 +++++++++++
>>>  target/arm/kvm_arm.h | 14 ++++++++++++++
>>>  3 files changed, 31 insertions(+), 6 deletions(-)
>>>
>>> diff --git a/target/arm/cpu64.c b/target/arm/cpu64.c
>>> index 1901997a0645..946994838d8a 100644
>>> --- a/target/arm/cpu64.c
>>> +++ b/target/arm/cpu64.c
>>> @@ -407,13 +407,13 @@ static void aarch64_cpu_set_aarch64(Object *obj, bool value, Error **errp)
>>>       * restriction allows us to avoid fixing up functionality that assumes a
>>>       * uniform execution state like do_interrupt.
>>>       */> -    if (!kvm_enabled()) {
>>> -        error_setg(errp, "'aarch64' feature cannot be disabled "
>>> -                         "unless KVM is enabled");
>>> -        return;
>>> -    }
>>> -
>>>      if (value == false) {
>>> +        if (!kvm_enabled() || !kvm_arm_aarch32_supported(CPU(cpu))) {
>>> +            error_setg(errp, "'aarch64' feature cannot be disabled "
>>> +                             "unless KVM is enabled and 32-bit EL1 "
>>> +                             "is supported");
>>> +            return;
>>> +        }
>>>          unset_feature(&cpu->env, ARM_FEATURE_AARCH64);
>>>      } else {
>>>          set_feature(&cpu->env, ARM_FEATURE_AARCH64);
>>> diff --git a/target/arm/kvm64.c b/target/arm/kvm64.c
>>> index 22d19c9aec6f..45ccda589903 100644
>>> --- a/target/arm/kvm64.c
>>> +++ b/target/arm/kvm64.c
>>> @@ -24,7 +24,9 @@
>>>  #include "exec/gdbstub.h"
>>>  #include "sysemu/sysemu.h"
>>>  #include "sysemu/kvm.h"
>>> +#include "sysemu/kvm_int.h"
>>>  #include "kvm_arm.h"
>>> +#include "hw/boards.h"
By the way those two new headers are not needed by this patch
>>>  #include "internals.h"
>>>  
>>>  static bool have_guest_debug;
>>> @@ -593,6 +595,15 @@ bool kvm_arm_get_host_cpu_features(ARMHostCPUFeatures *ahcf)
>>>      return true;
>>>  }
>>>  
>>> +bool kvm_arm_aarch32_supported(CPUState *cpu)
>>> +{
>>> +    KVMState *s = KVM_STATE(current_machine->accelerator);
>>> +    int ret;
>>> +
>>> +    ret = kvm_check_extension(s, KVM_CAP_ARM_EL1_32BIT);
>>> +    return ret > 0;
>> nit: return kvm_check_extension() should be sufficient
> 
> Ah yes, I forgot kvm_check_extension() already converts negative
> error codes to zero. I'll fix that for v3.
> 
>>> +}
>>> +
>>>  #define ARM_CPU_ID_MPIDR       3, 0, 0, 0, 5
>>>  
>>>  int kvm_arch_init_vcpu(CPUState *cs)
>>> diff --git a/target/arm/kvm_arm.h b/target/arm/kvm_arm.h
>>> index 2a07333c615f..812125f805a1 100644
>>> --- a/target/arm/kvm_arm.h
>>> +++ b/target/arm/kvm_arm.h
>>> @@ -207,6 +207,15 @@ bool kvm_arm_get_host_cpu_features(ARMHostCPUFeatures *ahcf);
>>>   */
>>>  void kvm_arm_set_cpu_features_from_host(ARMCPU *cpu);
>>>  
>>> +/**
>>> + * kvm_arm_aarch32_supported:
>>> + * @cs: CPUState
>> use kernel-doc comment style?
> 
> This file (kvm_arm.h) doesn't appear to have a super consistent comment
> style. I see some use @var: for the parameters and some have 'Returns:
> ...' lines as well. I'm happy to do whatever the maintainers prefer. For
> now I was just trying to mimic whatever caught my eye.>
>>> + *
>>> + * Returns true if the KVM VCPU can enable AArch32 mode and false
>>> + * otherwise.
>>> + */
>>> +bool kvm_arm_aarch32_supported(CPUState *cs);
>>> +
>>>  /**
>>>   * kvm_arm_get_max_vm_ipa_size - Returns the number of bits in the
>>>   * IPA address space supported by KVM
>>> @@ -247,6 +256,11 @@ static inline void kvm_arm_set_cpu_features_from_host(ARMCPU *cpu)
>>>      cpu->host_cpu_probe_failed = true;
>>>  }
>>>  
>>> +static inline bool kvm_arm_aarch32_supported(CPUState *cs)
>>> +{
>>> +    return false;
>>> +}
>>> +
>>>  static inline int kvm_arm_get_max_vm_ipa_size(MachineState *ms)
>>>  {
>>>      return -ENOENT;
>>>
>> Reviewed-by: Eric Auger <eric.auger@redhat.com>
Thanks

Eric
>>
> 
> Thanks,
> drew 
>