On 03.05.2013, at 13:08, Alexander Graf wrote:
>
>
> Am 03.05.2013 um 12:48 schrieb Bhushan Bharat-R65777 <R65777@xxxxxxxxxxxxx>:
>
>>>>>> +static void kvmppc_booke_vcpu_load_debug_regs(struct kvm_vcpu
>>>>>> +*vcpu) {
>>>>>> + if (!vcpu->arch.debug_active)
>>>>>> + return;
>>>>>> +
>>>>>> + /* Disable all debug events and clead pending debug events */
>>>>>> + mtspr(SPRN_DBCR0, 0x0);
>>>>>> + kvmppc_clear_dbsr();
>>>>>> +
>>>>>> + /*
>>>>>> + * Check whether guest still need debug resource, if not then there
>>>>>> + * is no need to restore guest context.
>>>>>> + */
>>>>>> + if (!vcpu->arch.shadow_dbg_reg.dbcr0)
>>>>>> + return;
>>>>>> +
>>>>>> + /* Load Guest Context */
>>>>>> + mtspr(SPRN_DBCR1, vcpu->arch.shadow_dbg_reg.dbcr1);
>>>>>> + mtspr(SPRN_DBCR2, vcpu->arch.shadow_dbg_reg.dbcr2); #ifdef
>>>>>> +CONFIG_KVM_E500MC
>>>>>> + mtspr(SPRN_DBCR4, vcpu->arch.shadow_dbg_reg.dbcr4);
>>>>>
>>>>> You need to make sure DBCR4 is 0 when you leave things back to normal
>>>>> user space. Otherwise guest debug can interfere with host debug.
>>>>
>>>>
>>>> ok
>>>>
>>>>>
>>>>>> +#endif
>>>>>> + mtspr(SPRN_IAC1, vcpu->arch.shadow_dbg_reg.iac[0]);
>>>>>> + mtspr(SPRN_IAC2, vcpu->arch.shadow_dbg_reg.iac[1]);
>>>>>> +#if CONFIG_PPC_ADV_DEBUG_IACS > 2
>>>>>> + mtspr(SPRN_IAC3, vcpu->arch.shadow_dbg_reg.iac[2]);
>>>>>> + mtspr(SPRN_IAC4, vcpu->arch.shadow_dbg_reg.iac[3]);
>>>>>> +#endif
>>>>>> + mtspr(SPRN_DAC1, vcpu->arch.shadow_dbg_reg.dac[0]);
>>>>>> + mtspr(SPRN_DAC2, vcpu->arch.shadow_dbg_reg.dac[1]);
>>>>>> +
>>>>>> + /* Enable debug events after other debug registers restored */
>>>>>> + mtspr(SPRN_DBCR0, vcpu->arch.shadow_dbg_reg.dbcr0); }
>>>>>
>>>>> All of the code above looks suspiciously similar to
>>>>> prime_debug_regs();. Can't we somehow reuse that?
>>>>
>>>> I think we can if
>>>> - Save thread->debug_regs in local data structure
>>>
>>> Yes, it can even be on the stack.
>>>
>>>> - Load vcpu->arch->debug_regs in thread->debug_regs
>>>> - Call prime_debug_regs();
>>>> - Restore thread->debug_regs from local save values in first step
>>>
>>> On heavyweight exit, based on the values on stack, yes.
>>
>> This is how I think we can save/restore debug context. Please correct if I am missing something.
>
> Sounds about right :)
Actually, what happens if a guest breakpoint is set to a kernel address that happens to be within the scope of kvm code? We do accept debug events between vcpu_run and the assembly code, right?
Alex
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