linux-kernel - Re: [PATCH v2 5/6] KVM: s390: interrupt: Fix single-stepping ISKE

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Date:   Fri, 21 Jul 2023 16:23:16 +0200
From:   Christian Borntraeger <borntraeger@...ux.ibm.com>
To:     Ilya Leoshkevich <iii@...ux.ibm.com>,
        Janosch Frank <frankja@...ux.ibm.com>,
        Claudio Imbrenda <imbrenda@...ux.ibm.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>
Cc:     David Hildenbrand <david@...hat.com>,
        Sven Schnelle <svens@...ux.ibm.com>, kvm@...r.kernel.org,
        linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
        Jens Freimann <jfreimann@...hat.com>
Subject: Re: [PATCH v2 5/6] KVM: s390: interrupt: Fix single-stepping ISKE



Am 21.07.23 um 13:57 schrieb Ilya Leoshkevich:
> kvm_s390_skey_check_enable() does not emulate any instructions, rather,
> it clears CPUSTAT_KSS and arranges for ISKE to run again. Therefore,
> skip the PER check and let ISKE run happen. Otherwise a debugger will
> see two single-step events on the same ISKE.

The same would be true for all instruction triggering a keyless mode exit,
like SSKE, RRBE but also LPSWE with a keyed PSW, no?
> 
> Signed-off-by: Ilya Leoshkevich <iii@...ux.ibm.com>

Reviewed-by: Christian Borntraeger <borntraeger@...ux.ibm.com>
> ---
>   arch/s390/kvm/intercept.c | 3 +--
>   1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/arch/s390/kvm/intercept.c b/arch/s390/kvm/intercept.c
> index d2f7940c5d03..8793cec066a6 100644
> --- a/arch/s390/kvm/intercept.c
> +++ b/arch/s390/kvm/intercept.c
> @@ -630,8 +630,7 @@ int kvm_handle_sie_intercept(struct kvm_vcpu *vcpu)
>   		rc = handle_partial_execution(vcpu);
>   		break;
>   	case ICPT_KSS:
> -		rc = kvm_s390_skey_check_enable(vcpu);
> -		break;

maybe add a comment here: /* Instruction will be redriven, skip the PER check */
> +		return kvm_s390_skey_check_enable(vcpu);

>   	case ICPT_MCHKREQ:
>   	case ICPT_INT_ENABLE:
>   		/*