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

Alexander Graf
2014-09-08T13:05:04Z

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 <maddy@linux.vnet.ibm.com>
> ---
> 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;
> }
>