linux-kernel - Re: [PATCH v3 3/6] KVM: s390: interrupt: Fix single-stepping kernel-emulated instructions

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Date:   Tue, 25 Jul 2023 14:04:36 +0200
From:   Claudio Imbrenda <imbrenda@...ux.ibm.com>
To:     Ilya Leoshkevich <iii@...ux.ibm.com>
Cc:     Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Janosch Frank <frankja@...ux.ibm.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        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 v3 3/6] KVM: s390: interrupt: Fix single-stepping
 kernel-emulated instructions

On Mon, 24 Jul 2023 11:44:09 +0200
Ilya Leoshkevich <iii@...ux.ibm.com> wrote:

> Single-stepping a kernel-emulated instruction that generates an
> interrupt causes GDB to land on the instruction following it instead of
> the respective interrupt handler.
> 
> The reason is that kvm_handle_sie_intercept(), after injecting the
> interrupt, also processes the PER event and arranges a KVM_SINGLESTEP
> exit. The interrupt is not yet delivered, however, so the userspace
> sees the next instruction.
> 
> Fix by avoiding the KVM_SINGLESTEP exit when there is a pending
> interrupt. The next __vcpu_run() loop iteration will arrange a
> KVM_SINGLESTEP exit after delivering the interrupt.
> 
> Reviewed-by: David Hildenbrand <david@...hat.com>

Reviewed-by: Claudio Imbrenda <imbrenda@...ux.ibm.com>

> Signed-off-by: Ilya Leoshkevich <iii@...ux.ibm.com>
> ---
>  arch/s390/kvm/intercept.c | 17 ++++++++++++++---
>  1 file changed, 14 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/s390/kvm/intercept.c b/arch/s390/kvm/intercept.c
> index 7cdd927541b0..d2f7940c5d03 100644
> --- a/arch/s390/kvm/intercept.c
> +++ b/arch/s390/kvm/intercept.c
> @@ -583,6 +583,19 @@ static int handle_pv_notification(struct kvm_vcpu *vcpu)
>  	return handle_instruction(vcpu);
>  }
>  
> +static bool should_handle_per_ifetch(const struct kvm_vcpu *vcpu, int rc)
> +{
> +	/* Process PER, also if the instruction is processed in user space. */
> +	if (!(vcpu->arch.sie_block->icptstatus & 0x02))
> +		return false;
> +	if (rc != 0 && rc != -EOPNOTSUPP)
> +		return false;
> +	if (guestdbg_sstep_enabled(vcpu) && vcpu->arch.local_int.pending_irqs)
> +		/* __vcpu_run() will exit after delivering the interrupt. */
> +		return false;
> +	return true;
> +}
> +
>  int kvm_handle_sie_intercept(struct kvm_vcpu *vcpu)
>  {
>  	int rc, per_rc = 0;
> @@ -645,9 +658,7 @@ int kvm_handle_sie_intercept(struct kvm_vcpu *vcpu)
>  		return -EOPNOTSUPP;
>  	}
>  
> -	/* process PER, also if the instruction is processed in user space */
> -	if (vcpu->arch.sie_block->icptstatus & 0x02 &&
> -	    (!rc || rc == -EOPNOTSUPP))
> +	if (should_handle_per_ifetch(vcpu, rc))
>  		per_rc = kvm_s390_handle_per_ifetch_icpt(vcpu);
>  	return per_rc ? per_rc : rc;
>  }