Re: [Qemu-devel] [PATCH v9 1/6] target-arm: kvm64 - introduce kvm_arm_init_debug()

[Peter Maydell]

On 20 November 2015 at 15:05, Peter Maydell <address@hidden> wrote:
> On 12 November 2015 at 16:20, Alex Bennée <address@hidden> wrote:
>> As we haven't always had guest debug support we need to probe for it.
>> Additionally we don't do this in the start-up capability code so we
>> don't fall over on old kernels.
>>
>> Signed-off-by: Alex Bennée <address@hidden>
>> ---
>>  target-arm/kvm64.c | 18 ++++++++++++++++++
>>  1 file changed, 18 insertions(+)
>>
>> diff --git a/target-arm/kvm64.c b/target-arm/kvm64.c
>> index ceebfeb..d087794 100644
>> --- a/target-arm/kvm64.c
>> +++ b/target-arm/kvm64.c
>> @@ -25,6 +25,22 @@
>>  #include "internals.h"
>>  #include "hw/arm/arm.h"
>>
>> +static bool have_guest_debug;
>> +
>> +/**
>> + * kvm_arm_init_debug()
>> + * @cs: CPUState
>> + *
>> + * Check for guest debug capabilities.
>> + *
>> + */
>> +static void kvm_arm_init_debug(CPUState *cs)
>> +{
>> +    have_guest_debug = kvm_check_extension(cs->kvm_state,
>> +                                           KVM_CAP_SET_GUEST_DEBUG);
>> +    return;
>> +}
>> +
>>  static inline void set_feature(uint64_t *features, int feature)
>>  {
>>      *features |= 1ULL << feature;
>> @@ -121,6 +137,8 @@ int kvm_arch_init_vcpu(CPUState *cs)
>>      }
>>      cpu->mp_affinity = mpidr & ARM64_AFFINITY_MASK;
>>
>> +    kvm_arm_init_debug(cs);
>> +
>>      return kvm_arm_init_cpreg_list(cpu);
>>  }
>
> I assume in practice the kernel guarantees that either all
> CPUs have the SET_GUEST_DEBUG cap, or none do :-)
>
> Reviewed-by: Peter Maydell <address@hidden>

...except I've just noticed that nothing else in this patchset
ever reads the have_guest_debug bool we just set, so what is
the purpose of this patch?

thanks
-- PMM