Re: [PATCH] KVM: PPC: booke: Added DECAR support

[Alexander Graf <agraf@suse.de>]

On 05/16/2012 08:57 AM, Bhushan Bharat-R65777 wrote:
>
>> -----Original Message-----
>> From: Alexander Graf [mailto:agraf@suse.de]
>> Sent: Tuesday, May 15, 2012 7:59 PM
>> To: Bhushan Bharat-R65777
>> Cc: kvm-ppc@vger.kernel.org; Bhushan Bharat-R65777
>> Subject: Re: [PATCH] KVM: PPC: booke: Added DECAR support
>>
>> On 05/15/2012 09:33 AM, Bharat Bhushan wrote:
>>> Added the decrementer auto-reload support.
>>>
>>> Signed-off-by: Bharat Bhushan<bharat.bhushan@freescale.com>
>>> ---
>>>    arch/powerpc/include/asm/kvm_host.h |    2 ++
>>>    arch/powerpc/kvm/booke.c            |    5 +++++
>>>    arch/powerpc/kvm/booke_emulate.c    |    7 ++++++-
>>>    3 files changed, 13 insertions(+), 1 deletions(-)
>>>
>>> diff --git a/arch/powerpc/include/asm/kvm_host.h
>>> b/arch/powerpc/include/asm/kvm_host.h
>>> index d848cdc..1d6f89e 100644
>>> --- a/arch/powerpc/include/asm/kvm_host.h
>>> +++ b/arch/powerpc/include/asm/kvm_host.h
>>> @@ -414,7 +414,9 @@ struct kvm_vcpu_arch {
>>>    	ulong mcsrr1;
>>>    	ulong mcsr;
>>>    	u32 dec;
>>> +#ifdef CONFIG_BOOKE
>>>    	u32 decar;
>>> +#endif
>>>    	u32 tbl;
>>>    	u32 tbu;
>>>    	u32 tcr;
>>> diff --git a/arch/powerpc/kvm/booke.c b/arch/powerpc/kvm/booke.c index
>>> 72f13f4..86681ee 100644
>>> --- a/arch/powerpc/kvm/booke.c
>>> +++ b/arch/powerpc/kvm/booke.c
>>> @@ -1267,6 +1267,11 @@ void kvmppc_decrementer_func(unsigned long data)
>>>    {
>>>    	struct kvm_vcpu *vcpu = (struct kvm_vcpu *)data;
>>>
>>> +	if (vcpu->arch.tcr&   TCR_ARE) {
>>> +		vcpu->arch.dec = vcpu->arch.decar;
>>> +		kvmppc_emulate_dec(vcpu);
>>> +	}
>>> +
>>>    	kvmppc_set_tsr_bits(vcpu, TSR_DIS);
>>>    }
>>>
>>> diff --git a/arch/powerpc/kvm/booke_emulate.c
>>> b/arch/powerpc/kvm/booke_emulate.c
>>> index 6c76397..83c3796 100644
>>> --- a/arch/powerpc/kvm/booke_emulate.c
>>> +++ b/arch/powerpc/kvm/booke_emulate.c
>>> @@ -129,6 +129,9 @@ int kvmppc_booke_emulate_mtspr(struct kvm_vcpu *vcpu, int
>> sprn, ulong spr_val)
>>>    		kvmppc_set_tcr(vcpu, spr_val);
>>>    		break;
>>>
>>> +	case SPRN_DECAR:
>>> +		vcpu->arch.decar = spr_val;
>>> +		break;
>>>    	/*
>>>    	 * Note: SPRG4-7 are user-readable.
>>>    	 * These values are loaded into the real SPRGs when resuming the @@
>>> -244,7 +247,9 @@ int kvmppc_booke_emulate_mfspr(struct kvm_vcpu *vcpu, int
>> sprn, ulong *spr_val)
>>>    	case SPRN_TCR:
>>>    		*spr_val = vcpu->arch.tcr;
>>>    		break;
>>> -
>>> +	case SPRN_DECAR:
>>> +		*spr_val = vcpu->arch.decar;
>>> +		break;
>> DECAR can't be read. Otherwise looks good to me.
> DECAR can be read on e500mc cores. So I will make this under CONFIG_KVM_E500MC.
>
> What happens if DECAR is read on non e500mc? Is it treated as NOP or illegal instruction exception?

I would assume the latter. NOPs usually don't happen. If anything, it 
would return 0.

See section 9.4 in the PowerISA:

The contents of the Decrementer Auto-Reload Register
cannot be read. The contents of bits 32:63 of register
RS can be written to the Decrementer Auto-Reload
Register using the mtspr instruction.

Could you please paste the respective passage of the e500mc manual that 
declares DECAR as readable?


Alex