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 :)
Alex
>
> 1) When QEMU is running
>
> -> thread->debug_reg == QEMU debug register context.
> -> Kernel will handle switching the debug register on context switch.
> -> no vcpu_load() called
>
> 2) QEMU makes ioctls (except RUN)
> -> This will call vcpu_load()
> -> should not change context.
> -> Some ioctls can change vcpu debug register, context saved in vcpu->debug_regs
>
> 3) QEMU Makes RUN ioctl
> -> Save thread->debug_reg on STACK
> -> Store thread->debug_reg == vcpu->debug_reg
> -> load thread->debug_reg
> -> RUN VCPU ( So thread points to vcpu context )
>
> 4) Context switch happens When VCPU running
> -> makes vcpu_load() should not load any context
> -> kernel loads the vcpu context as thread->debug_regs points to vcpu context.
>
> 5) On heavyweight_exit
> -> Load the context saved on stack in thread->debug_reg
>
> Thanks
> -Bharat
>
>
>
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