Subject: Re: [PATCH 1/2 v5] powerpc/kvm: support to handle sw breakpoint

From: Alexander Graf <[email-masked]>
Date: Mon, 08 Sep 2014 15:05:04 +0200

On 07.09.14 18:31, Madhavan Srinivasan wrote:
> This patch adds kernel side support for software breakpoint.
> Design is that, by using an illegal instruction, we trap to hypervisor
> via Emulation Assistance interrupt, where we check for the illegal instruction
> and accordingly we return to Host or Guest. Patch also adds support for
> software breakpoint in PR KVM.
> 
> Signed-off-by: Madhavan Srinivasan <[email-masked]>
> ---
>  arch/powerpc/include/asm/kvm_ppc.h |  6 ++++++
>  arch/powerpc/kvm/book3s.c          |  3 ++-
>  arch/powerpc/kvm/book3s_hv.c       | 41 ++++++++++++++++++++++++++++++++++----
>  arch/powerpc/kvm/book3s_pr.c       |  3 +++
>  arch/powerpc/kvm/emulate.c         | 18 +++++++++++++++++
>  5 files changed, 66 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/powerpc/include/asm/kvm_ppc.h b/arch/powerpc/include/asm/kvm_ppc.h
> index fb86a22..dd83c9a 100644
> --- a/arch/powerpc/include/asm/kvm_ppc.h
> +++ b/arch/powerpc/include/asm/kvm_ppc.h
> @@ -38,6 +38,12 @@
>  #include <asm/paca.h>
>  #endif
>  
> +/*
> + * KVMPPC_INST_SW_BREAKPOINT is debug Instruction
> + * for supporting software breakpoint.
> + */
> +#define KVMPPC_INST_SW_BREAKPOINT	0x00dddd00
> +
>  enum emulation_result {
>  	EMULATE_DONE,         /* no further processing */
>  	EMULATE_DO_MMIO,      /* kvm_run filled with MMIO request */
> diff --git a/arch/powerpc/kvm/book3s.c b/arch/powerpc/kvm/book3s.c
> index dd03f6b..00e9c9f 100644
> --- a/arch/powerpc/kvm/book3s.c
> +++ b/arch/powerpc/kvm/book3s.c
> @@ -778,7 +778,8 @@ int kvm_arch_vcpu_ioctl_translate(struct kvm_vcpu *vcpu,
>  int kvm_arch_vcpu_ioctl_set_guest_debug(struct kvm_vcpu *vcpu,
>  					struct kvm_guest_debug *dbg)
>  {
> -	return -EINVAL;
> +	vcpu->guest_debug = dbg->control;
> +	return 0;
>  }
>  
>  void kvmppc_decrementer_func(unsigned long data)
> diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
> index 27cced9..3a2414c 100644
> --- a/arch/powerpc/kvm/book3s_hv.c
> +++ b/arch/powerpc/kvm/book3s_hv.c
> @@ -725,6 +725,30 @@ static int kvmppc_hcall_impl_hv(unsigned long cmd)
>  	return kvmppc_hcall_impl_hv_realmode(cmd);
>  }
>  
> +static int kvmppc_emulate_debug_inst(struct kvm_run *run,
> +					struct kvm_vcpu *vcpu)
> +{
> +	u32 last_inst;
> +
> +	if(kvmppc_get_last_inst(vcpu, INST_GENERIC, &last_inst) !=
> +					EMULATE_DONE) {
> +		/*
> +		 * Fetch failed, so return to guest and
> +		 * try executing it again.
> +		 */
> +		return RESUME_GUEST;

Please end the if() here. In the kernel we usually treat abort
situations as separate.

> +	} else {
> +		if (last_inst == KVMPPC_INST_SW_BREAKPOINT) {
> +			run->exit_reason = KVM_EXIT_DEBUG;
> +			run->debug.arch.address = kvmppc_get_pc(vcpu);
> +			return RESUME_HOST;
> +		} else {
> +			kvmppc_core_queue_program(vcpu, SRR1_PROGILL);
> +			return RESUME_GUEST;
> +		}
> +	}
> +}
> +
>  static int kvmppc_handle_exit_hv(struct kvm_run *run, struct kvm_vcpu *vcpu,
>  				 struct task_struct *tsk)
>  {
> @@ -807,12 +831,18 @@ static int kvmppc_handle_exit_hv(struct kvm_run *run, struct kvm_vcpu *vcpu,
>  		break;
>  	/*
>  	 * This occurs if the guest executes an illegal instruction.
> -	 * We just generate a program interrupt to the guest, since
> -	 * we don't emulate any guest instructions at this stage.
> +	 * If the guest debug is disabled, generate a program interrupt
> +	 * to the guest. If guest debug is enabled, we need to check
> +	 * whether the instruction is a software breakpoint instruction.
> +	 * Accordingly return to Guest or Host.
>  	 */
>  	case BOOK3S_INTERRUPT_H_EMUL_ASSIST:
> -		kvmppc_core_queue_program(vcpu, SRR1_PROGILL);
> -		r = RESUME_GUEST;
> +		if(vcpu->guest_debug & KVM_GUESTDBG_USE_SW_BP) {
> +			r = kvmppc_emulate_debug_inst(run, vcpu);
> +		} else {
> +			kvmppc_core_queue_program(vcpu, SRR1_PROGILL);
> +			r = RESUME_GUEST;
> +		}
>  		break;
>  	/*
>  	 * This occurs if the guest (kernel or userspace), does something that
> @@ -922,6 +952,9 @@ static int kvmppc_get_one_reg_hv(struct kvm_vcpu *vcpu, u64 id,
>  	long int i;
>  
>  	switch (id) {
> +	case KVM_REG_PPC_DEBUG_INST:
> +		*val = get_reg_val(id, KVMPPC_INST_SW_BREAKPOINT);
> +		break;
>  	case KVM_REG_PPC_HIOR:
>  		*val = get_reg_val(id, 0);
>  		break;
> diff --git a/arch/powerpc/kvm/book3s_pr.c b/arch/powerpc/kvm/book3s_pr.c
> index faffb27..6d73708 100644
> --- a/arch/powerpc/kvm/book3s_pr.c
> +++ b/arch/powerpc/kvm/book3s_pr.c
> @@ -1319,6 +1319,9 @@ static int kvmppc_get_one_reg_pr(struct kvm_vcpu *vcpu, u64 id,
>  	int r = 0;
>  
>  	switch (id) {
> +	case KVM_REG_PPC_DEBUG_INST:
> +		*val = get_reg_val(id, KVMPPC_INST_SW_BREAKPOINT);
> +		break;
>  	case KVM_REG_PPC_HIOR:
>  		*val = get_reg_val(id, to_book3s(vcpu)->hior);
>  		break;
> diff --git a/arch/powerpc/kvm/emulate.c b/arch/powerpc/kvm/emulate.c
> index e96b50d..30f326b 100644
> --- a/arch/powerpc/kvm/emulate.c
> +++ b/arch/powerpc/kvm/emulate.c
> @@ -274,6 +274,24 @@ int kvmppc_emulate_instruction(struct kvm_run *run, struct kvm_vcpu *vcpu)
>  		}
>  		break;
>  
> +	case 0:
> +		/*
> +		 * Instruction with primary opcode 0. Based on PowerISA
> +		 * these are illegal instructions.
> +		 */
> +		if(inst == KVMPPC_INST_SW_BREAKPOINT) {

Here you're missing a space between if and (. Are you sure that you ran
checkpatch.pl?

> +			run->exit_reason = KVM_EXIT_DEBUG;
> +			run->debug.arch.address = kvmppc_get_pc(vcpu);
> +			emulated = EMULATE_EXIT_USER;
> +			advance = 0;
> +			printk(KERN_INFO "pr_emulate: debug instr \n");
> +		} else {
> +			kvmppc_core_queue_program(vcpu, SRR1_PROGILL);
> +			emulated = EMULATE_DONE;
> +			advance = 0;

Just set emulated = EMULATE_FAIL here, the same as default:.

Alex

> +		}
> +		break;	
> +
>  	default:
>  		emulated = EMULATE_FAIL;
>  	}