Subject: Re: [PATCH 1/4] KVM: PPC: BOOK3S: PR: Emulate virtual timebase register

From: "Aneesh Kumar K.V" <[email-masked]>
Date: Thu, 05 Jun 2014 21:20:28 +0530

Alexander Graf <[email-masked]> writes:

> On 05.06.14 14:08, Aneesh Kumar K.V wrote:
>> virtual time base register is a per VM, per cpu register that needs
>> to be saved and restored on vm exit and entry. Writing to VTB is not
>> allowed in the privileged mode.
>>
>> Signed-off-by: Aneesh Kumar K.V <[email-masked]>
>> ---
>>   arch/powerpc/include/asm/kvm_host.h |  1 +
>>   arch/powerpc/include/asm/reg.h      | 15 +++++++++++++++
>>   arch/powerpc/include/asm/time.h     |  9 +++++++++
>>   arch/powerpc/kvm/book3s.c           |  6 ++++++
>>   arch/powerpc/kvm/book3s_emulate.c   |  3 +++
>>   arch/powerpc/kvm/book3s_hv.c        |  6 ------
>>   arch/powerpc/kvm/book3s_pr.c        |  3 ++-
>>   7 files changed, 36 insertions(+), 7 deletions(-)
>>
>> diff --git a/arch/powerpc/include/asm/kvm_host.h b/arch/powerpc/include/asm/kvm_host.h
>> index 4a58731a0a72..bd3caeaeebe1 100644
>> --- a/arch/powerpc/include/asm/kvm_host.h
>> +++ b/arch/powerpc/include/asm/kvm_host.h
>> @@ -505,6 +505,7 @@ struct kvm_vcpu_arch {
>>   #endif
>>   	/* Time base value when we entered the guest */
>>   	u64 entry_tb;
>> +	u64 entry_vtb;
>>   	u32 tcr;
>>   	ulong tsr; /* we need to perform set/clr_bits() which requires ulong */
>>   	u32 ivor[64];
>> diff --git a/arch/powerpc/include/asm/reg.h b/arch/powerpc/include/asm/reg.h
>> index 4852bcf270f3..3e7085d8af90 100644
>> --- a/arch/powerpc/include/asm/reg.h
>> +++ b/arch/powerpc/include/asm/reg.h
>> @@ -25,6 +25,7 @@
>>   #ifdef CONFIG_8xx
>>   #include <asm/reg_8xx.h>
>>   #endif /* CONFIG_8xx */
>> +#include <asm/bug.h>
>>   
>>   #define MSR_SF_LG	63              /* Enable 64 bit mode */
>>   #define MSR_ISF_LG	61              /* Interrupt 64b mode valid on 630 */
>> @@ -1193,6 +1194,20 @@
>>   				     : "r" ((unsigned long)(v)) \
>>   				     : "memory")
>>   
>> +static inline unsigned long mfvtb (void)
>> +{
>> +#ifdef CONFIG_PPC_BOOK3S_64
>> +	if (cpu_has_feature(CPU_FTR_ARCH_207S))
>> +		return mfspr(SPRN_VTB);
>> +#endif
>> +	/*
>> +	 * The above mfspr will be a no-op on anything before Power8
>> +	 * That can result in random values returned. We need to
>> +	 * capture that.
>> +	 */
>> +	BUG();
>> +}
>> +
>>   #ifdef __powerpc64__
>>   #if defined(CONFIG_PPC_CELL) || defined(CONFIG_PPC_FSL_BOOK3E)
>>   #define mftb()		({unsigned long rval;				\
>> diff --git a/arch/powerpc/include/asm/time.h b/arch/powerpc/include/asm/time.h
>> index 1d428e6007ca..03cbada59d3a 100644
>> --- a/arch/powerpc/include/asm/time.h
>> +++ b/arch/powerpc/include/asm/time.h
>> @@ -102,6 +102,15 @@ static inline u64 get_rtc(void)
>>   	return (u64)hi * 1000000000 + lo;
>>   }
>>   
>> +static inline u64 get_vtb(void)
>> +{
>> +#ifdef CONFIG_PPC_BOOK3S_64
>> +	if (cpu_has_feature(CPU_FTR_ARCH_207S))
>> +		return mfvtb();
>> +#endif
>> +	return 0;
>> +}
>> +
>>   #ifdef CONFIG_PPC64
>>   static inline u64 get_tb(void)
>>   {
>> diff --git a/arch/powerpc/kvm/book3s.c b/arch/powerpc/kvm/book3s.c
>> index 52c654dbd41a..ae43e4178ecd 100644
>> --- a/arch/powerpc/kvm/book3s.c
>> +++ b/arch/powerpc/kvm/book3s.c
>> @@ -646,6 +646,9 @@ int kvm_vcpu_ioctl_get_one_reg(struct kvm_vcpu *vcpu, struct kvm_one_reg *reg)
>>   		case KVM_REG_PPC_BESCR:
>>   			val = get_reg_val(reg->id, vcpu->arch.bescr);
>>   			break;
>> +		case KVM_REG_PPC_VTB:
>> +			val = get_reg_val(reg->id, vcpu->arch.vtb);
>> +			break;
>>   		default:
>>   			r = -EINVAL;
>>   			break;
>> @@ -750,6 +753,9 @@ int kvm_vcpu_ioctl_set_one_reg(struct kvm_vcpu *vcpu, struct kvm_one_reg *reg)
>>   		case KVM_REG_PPC_BESCR:
>>   			vcpu->arch.bescr = set_reg_val(reg->id, val);
>>   			break;
>> +		case KVM_REG_PPC_VTB:
>> +			vcpu->arch.vtb = set_reg_val(reg->id, val);
>> +			break;
>>   		default:
>>   			r = -EINVAL;
>>   			break;
>> diff --git a/arch/powerpc/kvm/book3s_emulate.c b/arch/powerpc/kvm/book3s_emulate.c
>> index 3565e775b61b..1bb16a59dcbc 100644
>> --- a/arch/powerpc/kvm/book3s_emulate.c
>> +++ b/arch/powerpc/kvm/book3s_emulate.c
>> @@ -577,6 +577,9 @@ int kvmppc_core_emulate_mfspr_pr(struct kvm_vcpu *vcpu, int sprn, ulong *spr_val
>>   		 */
>>   		*spr_val = vcpu->arch.spurr;
>>   		break;
>> +	case SPRN_VTB:
>> +		*spr_val = vcpu->arch.vtb;
>
> Doesn't this mean that vtb can be the same 2 when the guest reads it 2 
> times in a row without getting preempted?

But a mfspr will result in VM exit and that would make sure we
update vcpu->arch.vtb with the correct value.

-aneesh