[PATCH v2 02/10] KVM: PPC: Book3S HV: Save/restore new PMU registers

[Paul Mackerras]

On Wed, Jul 01, 2020 at 05:20:54AM -0400, Athira Rajeev wrote:
> PowerISA v3.1 has added new performance monitoring unit (PMU)
> special purpose registers (SPRs). They are
> 
> Monitor Mode Control Register 3 (MMCR3)
> Sampled Instruction Event Register A (SIER2)
> Sampled Instruction Event Register B (SIER3)
> 
> Patch addes support to save/restore these new
> SPRs while entering/exiting guest.

This mostly looks reasonable, at a quick glance at least, but I am
puzzled by two of the changes you are making.  See below.

> diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
> index 6bf66649..c265800 100644
> --- a/arch/powerpc/kvm/book3s_hv.c
> +++ b/arch/powerpc/kvm/book3s_hv.c
> @@ -1698,7 +1698,8 @@ static int kvmppc_get_one_reg_hv(struct kvm_vcpu *vcpu, u64 id,
>  		*val = get_reg_val(id, vcpu->arch.sdar);
>  		break;
>  	case KVM_REG_PPC_SIER:
> -		*val = get_reg_val(id, vcpu->arch.sier);
> +		i = id - KVM_REG_PPC_SIER;
> +		*val = get_reg_val(id, vcpu->arch.sier[i]);

This is inside a switch (id) statement, so here we know that id is
KVM_REG_PPC_SIER.  In other words i will always be zero, so what is
the point of doing the subtraction?

>  		break;
>  	case KVM_REG_PPC_IAMR:
>  		*val = get_reg_val(id, vcpu->arch.iamr);
> @@ -1919,7 +1920,8 @@ static int kvmppc_set_one_reg_hv(struct kvm_vcpu *vcpu, u64 id,
>  		vcpu->arch.sdar = set_reg_val(id, *val);
>  		break;
>  	case KVM_REG_PPC_SIER:
> -		vcpu->arch.sier = set_reg_val(id, *val);
> +		i = id - KVM_REG_PPC_SIER;
> +		vcpu->arch.sier[i] = set_reg_val(id, *val);

Same comment here.

I think that new defines for the new registers will need to be added
to arch/powerpc/include/uapi/asm/kvm.h and
Documentation/virt/kvm/api.rst, and then new cases will need to be
added to these switch statements.

By the way, please cc kvm-ppc at vger.kernel.org and kvm at vger.kernel.org
on KVM patches.

Paul.