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Message-ID: <b9ecc108-aa14-d11c-1314-cbf21a2548f1@redhat.com>
Date:   Mon, 24 Jul 2023 10:26:18 +0200
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Subject: Re: [PATCH v2 2/6] KVM: s390: interrupt: Fix single-stepping into
 program interrupt handlers
Content-Language: en-US
To:     Ilya Leoshkevich <iii@linux.ibm.com>,
        Christian Borntraeger <borntraeger@linux.ibm.com>,
        Janosch Frank <frankja@linux.ibm.com>,
        Claudio Imbrenda <imbrenda@linux.ibm.com>,
        Heiko Carstens <hca@linux.ibm.com>,
        Vasily Gorbik <gor@linux.ibm.com>,
        Alexander Gordeev <agordeev@linux.ibm.com>
Cc:     Sven Schnelle <svens@linux.ibm.com>, kvm@vger.kernel.org,
        linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org,
        Jens Freimann <jfreimann@redhat.com>
References: <20230721120046.2262291-1-iii@linux.ibm.com>
 <20230721120046.2262291-3-iii@linux.ibm.com>
From:   David Hildenbrand <david@redhat.com>
Organization: Red Hat
In-Reply-To: <20230721120046.2262291-3-iii@linux.ibm.com>
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Precedence: bulk

On 21.07.23 13:57, Ilya Leoshkevich wrote:
> Currently, after single-stepping an instruction that generates a
> specification exception, GDB ends up on the instruction immediately
> following it.
> 
> The reason is that vcpu_post_run() injects the interrupt and sets
> KVM_GUESTDBG_EXIT_PENDING, causing a KVM_SINGLESTEP exit. The
> interrupt is not delivered, however, therefore userspace sees the
> address of the next instruction.
> 
> Fix by letting the __vcpu_run() loop go into the next iteration,
> where vcpu_pre_run() delivers the interrupt and sets
> KVM_GUESTDBG_EXIT_PENDING.
> 
> Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
> ---
>   arch/s390/kvm/intercept.c | 19 +++++++++++++++++--
>   1 file changed, 17 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/s390/kvm/intercept.c b/arch/s390/kvm/intercept.c
> index 954d39adf85c..7cdd927541b0 100644
> --- a/arch/s390/kvm/intercept.c
> +++ b/arch/s390/kvm/intercept.c
> @@ -226,7 +226,22 @@ static int handle_itdb(struct kvm_vcpu *vcpu)
>   	return 0;
>   }
>   
> -#define per_event(vcpu) (vcpu->arch.sie_block->iprcc & PGM_PER)
> +static bool should_handle_per_event(const struct kvm_vcpu *vcpu)
> +{
> +	if (!guestdbg_enabled(vcpu))
> +		return false;
> +	if (!(vcpu->arch.sie_block->iprcc & PGM_PER))
> +		return false;
> +	if (guestdbg_sstep_enabled(vcpu) &&
> +	    vcpu->arch.sie_block->iprcc != PGM_PER) {
> +		/*
> +		 * __vcpu_run() will exit after delivering the concurrently
> +		 * indicated condition.
> +		 */
> +		return false;
> +	}
> +	return true;
> +}
>   
>   static int handle_prog(struct kvm_vcpu *vcpu)
>   {
> @@ -242,7 +257,7 @@ static int handle_prog(struct kvm_vcpu *vcpu)
>   	if (kvm_s390_pv_cpu_is_protected(vcpu))
>   		return -EOPNOTSUPP;
>   
> -	if (guestdbg_enabled(vcpu) && per_event(vcpu)) {
> +	if (should_handle_per_event(vcpu)) {
>   		rc = kvm_s390_handle_per_event(vcpu);
>   		if (rc)
>   			return rc;

Reviewed-by: David Hildenbrand <david@redhat.com>

-- 
Cheers,

David / dhildenb