Re: [PATCH v3] KVM: PPC: Book3S PR: Do not fail emulation with mtspr/mfspr for unknown SPRs

[Thomas Huth <thuth@redhat.com>]

On 05.04.2017 15:58, Thomas Huth wrote:
> According to the PowerISA 2.07, mtspr and mfspr should not always
> generate an illegal instruction exception when being used with an
> undefined SPR, but rather treat the instruction as a NOP or inject a
> privilege exception in some cases, too - depending on the SPR number.
> Also turn the printk here into a ratelimited print statement, so that
> the guest can not flood the dmesg log of the host by issueing lots of
> illegal mtspr/mfspr instruction here.
> 
> Signed-off-by: Thomas Huth <thuth@redhat.com>
> ---
>  v3:
>  - Make sure that we do not advance the program counter after we've
>    already changed it due to injecting a program interrupt
> 
>  v2:
>  - Inject illegal instruction program interrupt instead of emulation
>    assist interrupt (according to the last programming note in section
>    6.5.9 of Book III of the PowerISA v2.07)
> 
>  arch/powerpc/kvm/book3s_emulate.c | 34 ++++++++++++++++++++++++++--------
>  arch/powerpc/kvm/emulate.c        |  8 ++++++++
>  2 files changed, 34 insertions(+), 8 deletions(-)
> 
> diff --git a/arch/powerpc/kvm/book3s_emulate.c b/arch/powerpc/kvm/book3s_emulate.c
> index 8359752..68d6898 100644
> --- a/arch/powerpc/kvm/book3s_emulate.c
> +++ b/arch/powerpc/kvm/book3s_emulate.c
> @@ -503,10 +503,18 @@ int kvmppc_core_emulate_mtspr_pr(struct kvm_vcpu *vcpu, int sprn, ulong spr_val)
>  		break;
>  unprivileged:
>  	default:
> -		printk(KERN_INFO "KVM: invalid SPR write: %d\n", sprn);
> -#ifndef DEBUG_SPR
> -		emulated = EMULATE_FAIL;
> -#endif
> +		pr_info_ratelimited("KVM: invalid SPR write: %d\n", sprn);
> +		if (sprn & 0x10) {
> +			if (kvmppc_get_msr(vcpu) & MSR_PR) {
> +				kvmppc_core_queue_program(vcpu, SRR1_PROGPRIV);
> +				emulated = EMULATE_AGAIN;
> +			}
> +		} else {
> +			if ((kvmppc_get_msr(vcpu) & MSR_PR) || sprn == 0) {
> +				kvmppc_core_queue_program(vcpu, SRR1_PROGILL);
> +				emulated = EMULATE_AGAIN;
> +			}
> +		}
>  		break;
>  	}
>  
> @@ -648,10 +656,20 @@ int kvmppc_core_emulate_mfspr_pr(struct kvm_vcpu *vcpu, int sprn, ulong *spr_val
>  		break;
>  	default:
>  unprivileged:
> -		printk(KERN_INFO "KVM: invalid SPR read: %d\n", sprn);
> -#ifndef DEBUG_SPR
> -		emulated = EMULATE_FAIL;
> -#endif
> +		pr_info_ratelimited("KVM: invalid SPR read: %d\n", sprn);
> +		if (sprn & 0x10) {
> +			if (kvmppc_get_msr(vcpu) & MSR_PR) {
> +				kvmppc_core_queue_program(vcpu, SRR1_PROGPRIV);
> +				emulated = EMULATE_AGAIN;
> +			}
> +		} else {
> +			if ((kvmppc_get_msr(vcpu) & MSR_PR) || sprn == 0 ||
> +			    sprn == 4 || sprn == 5 || sprn == 6) {
> +				kvmppc_core_queue_program(vcpu, SRR1_PROGILL);
> +				emulated = EMULATE_AGAIN;
> +			}
> +		}
> +
>  		break;
>  	}
>  
> diff --git a/arch/powerpc/kvm/emulate.c b/arch/powerpc/kvm/emulate.c
> index b379146..c873ffe 100644
> --- a/arch/powerpc/kvm/emulate.c
> +++ b/arch/powerpc/kvm/emulate.c
> @@ -259,10 +259,18 @@ int kvmppc_emulate_instruction(struct kvm_run *run, struct kvm_vcpu *vcpu)
>  
>  		case OP_31_XOP_MFSPR:
>  			emulated = kvmppc_emulate_mfspr(vcpu, sprn, rt);
> +			if (emulated == EMULATE_AGAIN) {
> +				emulated = EMULATE_DONE;
> +				advance = 0;
> +			}
>  			break;
>  
>  		case OP_31_XOP_MTSPR:
>  			emulated = kvmppc_emulate_mtspr(vcpu, sprn, rs);
> +			if (emulated == EMULATE_AGAIN) {
> +				emulated = EMULATE_DONE;
> +				advance = 0;
> +			}
>  			break;
>  
>  		case OP_31_XOP_TLBSYNC:
> 

Ping!

Paul, does this now look OK for you this way?

 Thomas