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

From: Alexander Graf <[email-masked]>
Date: Thu, 05 Jun 2014 14:19:24 +0200

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?

Alex

> +		break;
>   	case SPRN_GQR0:
>   	case SPRN_GQR1:
>   	case SPRN_GQR2:
> diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
> index aba05bbb3e74..f6ac58336b3f 100644
> --- a/arch/powerpc/kvm/book3s_hv.c
> +++ b/arch/powerpc/kvm/book3s_hv.c
> @@ -897,9 +897,6 @@ static int kvmppc_get_one_reg_hv(struct kvm_vcpu *vcpu, u64 id,
>   	case KVM_REG_PPC_IC:
>   		*val = get_reg_val(id, vcpu->arch.ic);
>   		break;
> -	case KVM_REG_PPC_VTB:
> -		*val = get_reg_val(id, vcpu->arch.vtb);
> -		break;
>   	case KVM_REG_PPC_CSIGR:
>   		*val = get_reg_val(id, vcpu->arch.csigr);
>   		break;
> @@ -1097,9 +1094,6 @@ static int kvmppc_set_one_reg_hv(struct kvm_vcpu *vcpu, u64 id,
>   	case KVM_REG_PPC_IC:
>   		vcpu->arch.ic = set_reg_val(id, *val);
>   		break;
> -	case KVM_REG_PPC_VTB:
> -		vcpu->arch.vtb = set_reg_val(id, *val);
> -		break;
>   	case KVM_REG_PPC_CSIGR:
>   		vcpu->arch.csigr = set_reg_val(id, *val);
>   		break;
> diff --git a/arch/powerpc/kvm/book3s_pr.c b/arch/powerpc/kvm/book3s_pr.c
> index ff15f8e31a27..96cdf89a8c86 100644
> --- a/arch/powerpc/kvm/book3s_pr.c
> +++ b/arch/powerpc/kvm/book3s_pr.c
> @@ -125,6 +125,7 @@ void kvmppc_copy_to_svcpu(struct kvmppc_book3s_shadow_vcpu *svcpu,
>   	 * to find the guest purr and spurr value.
>   	 */
>   	vcpu->arch.entry_tb = get_tb();
> +	vcpu->arch.entry_vtb = get_vtb();
>   	svcpu->in_use = true;
>   }
>   
> @@ -176,7 +177,7 @@ void kvmppc_copy_from_svcpu(struct kvm_vcpu *vcpu,
>   	 */
>   	vcpu->arch.purr += get_tb() - vcpu->arch.entry_tb;
>   	vcpu->arch.spurr += get_tb() - vcpu->arch.entry_tb;
> -
> +	vcpu->arch.vtb += get_vtb() - vcpu->arch.entry_vtb;
>   	svcpu->in_use = false;
>   
>   out: