Subject: Re: [PATCH v2] kvm-pr: manage single-step mode

From: David Gibson <[email-masked]>
Date: Mon, 11 Apr 2016 14:02:05 +1000

On Fri,  8 Apr 2016 18:05:00 +0200
Laurent Vivier <[email-masked]> wrote:

> Until now, when we connect gdb to the QEMU gdb-server, the
> single-step mode is not managed.
> 
> This patch adds this, only for kvm-pr:
> 
> If KVM_GUESTDBG_SINGLESTEP is set, we enable single-step trace bit in the
> MSR (MSR_SE) just before the __kvmppc_vcpu_run(), and disable it just after.
> In kvmppc_handle_exit_pr, instead of routing the interrupt to
> the guest, we return to host, with KVM_EXIT_DEBUG reason.
> 
> Signed-off-by: Laurent Vivier <[email-masked]>

Reviewed-by: David Gibson <[email-masked]>

> ---
> v2: split BOOK3S_INTERRUPT_MACHINE_CHECK and BOOK3S_INTERRUPT_TRACE
> 
>  arch/powerpc/kvm/book3s_pr.c | 32 +++++++++++++++++++++++++++++++-
>  1 file changed, 31 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/powerpc/kvm/book3s_pr.c b/arch/powerpc/kvm/book3s_pr.c
> index 95bceca..8129b0d 100644
> --- a/arch/powerpc/kvm/book3s_pr.c
> +++ b/arch/powerpc/kvm/book3s_pr.c
> @@ -882,6 +882,24 @@ void kvmppc_set_fscr(struct kvm_vcpu *vcpu, u64 fscr)
>  }
>  #endif
>  
> +static void kvmppc_setup_debug(struct kvm_vcpu *vcpu)
> +{
> +	if (vcpu->guest_debug & KVM_GUESTDBG_SINGLESTEP) {
> +		u64 msr = kvmppc_get_msr(vcpu);
> +
> +		kvmppc_set_msr(vcpu, msr | MSR_SE);
> +	}
> +}
> +
> +static void kvmppc_clear_debug(struct kvm_vcpu *vcpu)
> +{
> +	if (vcpu->guest_debug & KVM_GUESTDBG_SINGLESTEP) {
> +		u64 msr = kvmppc_get_msr(vcpu);
> +
> +		kvmppc_set_msr(vcpu, msr & ~MSR_SE);
> +	}
> +}
> +
>  int kvmppc_handle_exit_pr(struct kvm_run *run, struct kvm_vcpu *vcpu,
>  			  unsigned int exit_nr)
>  {
> @@ -1207,10 +1225,18 @@ program_interrupt:
>  		break;
>  #endif
>  	case BOOK3S_INTERRUPT_MACHINE_CHECK:
> -	case BOOK3S_INTERRUPT_TRACE:
>  		kvmppc_book3s_queue_irqprio(vcpu, exit_nr);
>  		r = RESUME_GUEST;
>  		break;
> +	case BOOK3S_INTERRUPT_TRACE:
> +		if (vcpu->guest_debug & KVM_GUESTDBG_SINGLESTEP) {
> +			run->exit_reason = KVM_EXIT_DEBUG;
> +			r = RESUME_HOST;
> +		} else {
> +			kvmppc_book3s_queue_irqprio(vcpu, exit_nr);
> +			r = RESUME_GUEST;
> +		}
> +		break;
>  	default:
>  	{
>  		ulong shadow_srr1 = vcpu->arch.shadow_srr1;
> @@ -1479,6 +1505,8 @@ static int kvmppc_vcpu_run_pr(struct kvm_run *kvm_run, struct kvm_vcpu *vcpu)
>  		goto out;
>  	}
>  
> +	kvmppc_setup_debug(vcpu);
> +
>  	/*
>  	 * Interrupts could be timers for the guest which we have to inject
>  	 * again, so let's postpone them until we're in the guest and if we
> @@ -1501,6 +1529,8 @@ static int kvmppc_vcpu_run_pr(struct kvm_run *kvm_run, struct kvm_vcpu *vcpu)
>  
>  	ret = __kvmppc_vcpu_run(kvm_run, vcpu);
>  
> +	kvmppc_clear_debug(vcpu);
> +
>  	/* No need for kvm_guest_exit. It's done in handle_exit.
>  	   We also get here with interrupts enabled. */
>  
> -- 
> 2.5.5
> 

-- 
David Gibson <[email-masked]>
Senior Software Engineer, Virtualization, Red Hat