Re: [PATCH v2 10/10] KVM: arm64: add trace points for guest_debug debug

Christoffer Dall
2015-04-14T10:24:32Z

On Tue, Mar 31, 2015 at 04:08:08PM +0100, Alex Bennée wrote:
> This includes trace points for:
> kvm_arch_setup_guest_debug
> kvm_arch_clear_guest_debug
> kvm_handle_guest_debug
>
> I've also added some generic register setting trace events so I can
> watch the register values being built up over time. The local
> dump_dbg_regs() function dumps all the HW BKPT and WPT registers.
>
> I've also added a #define trace_dreg to shorten some lines.
>
> Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
>
> diff --git a/arch/arm64/kvm/debug.c b/arch/arm64/kvm/debug.c
> index 638c111..7c96288 100644
> --- a/arch/arm64/kvm/debug.c
> +++ b/arch/arm64/kvm/debug.c
> @@ -25,12 +25,37 @@
> #include <asm/kvm_host.h>
> #include <asm/kvm_emulate.h>
>
> +#include "trace.h"
> +
> +#define trace_dreg(name, value) trace_kvm_arch_setup_debug_reg32(name, value)
> +
> /* These are the bits of MDSCR_EL1 we may mess with */
> #define MDSCR_EL1_DEBUG_BITS (DBG_MDSCR_SS | \
> DBG_MDSCR_KDE | \
> DBG_MDSCR_MDE)
>
> /**
> + * dump_dbg_regs - simple debug helper
> + *
> + * This provides a simple helper to dump the HW debug registers
> + */
> +static void dump_dbg_regs(struct kvm_vcpu *vcpu, int nb, int nw)
> +{
> + int i;
> +
> + for (i = 0; i < nb; i++) {
> + trace_printk("bkpt%d: 0x%08x:0x%llx\n", i,
> + (u32) vcpu_sys_reg(vcpu, DBGBCR0_EL1 + i),
> + vcpu_sys_reg(vcpu, DBGBVR0_EL1 + i));
> + }
> + for (i = 0; i < nb; i++) {
> + trace_printk("wtpt%d: 0x%08x:0x%llx\n", i,
> + (u32) vcpu_sys_reg(vcpu, DBGWCR0_EL1 + i),
> + vcpu_sys_reg(vcpu, DBGWVR0_EL1 + i));
> + }
> +}
> +
> +/**
> * kvm_arch_setup_debug - set-up debug related stuff
> *
> * @vcpu: the vcpu pointer
> @@ -52,9 +77,13 @@ void kvm_arch_setup_debug(struct kvm_vcpu *vcpu)
> {
> bool trap_debug = false;
>
> + trace_kvm_arch_setup_debug(vcpu->guest_debug);
> +
> vcpu->arch.mdcr_el2 |= (MDCR_EL2_TPM | MDCR_EL2_TPMCR);
> vcpu->arch.mdcr_el2 |= (MDCR_EL2_TDRA | MDCR_EL2_TDOSA);
>
> + trace_kvm_arch_setup_debug_reg32("MDCR_EL2", vcpu->arch.mdcr_el2);
> +
> /*
> * If we are not treating debug registers are dirty we need
> * to trap if the guest starts accessing them.
> @@ -66,6 +95,8 @@ void kvm_arch_setup_debug(struct kvm_vcpu *vcpu)
> if (vcpu->guest_debug) {
> vcpu->arch.mdcr_el2 |= MDCR_EL2_TDE;
>
> + trace_dreg("MDCR_EL2", vcpu->arch.mdcr_el2);
> +
> /* Save pstate/mdscr */
> vcpu_debug_saved_reg(vcpu, pstate_ss_bit) =
> *vcpu_cpsr(vcpu) & DBG_SPSR_SS;
> @@ -73,6 +104,11 @@ void kvm_arch_setup_debug(struct kvm_vcpu *vcpu)
> vcpu_debug_saved_reg(vcpu, mdscr_el1) =
> vcpu_sys_reg(vcpu, MDSCR_EL1);
>
> + trace_dreg("Save: PSTATE.SS",
> + vcpu_debug_saved_reg(vcpu, pstate_ss_bit));
> + trace_dreg("Save: MDSCR",
> + vcpu_debug_saved_reg(vcpu, mdscr_el1));
> +
> /*
> * Single Step (ARM ARM D2.12.3 The software step state
> * machine)
> @@ -88,6 +124,8 @@ void kvm_arch_setup_debug(struct kvm_vcpu *vcpu)
> *vcpu_cpsr(vcpu) &= ~DBG_SPSR_SS;
> vcpu_sys_reg(vcpu, MDSCR_EL1) &= ~DBG_MDSCR_SS;
> }
> + trace_dreg("SPSR_EL2", *vcpu_cpsr(vcpu));
> + trace_dreg("MDSCR_EL1", vcpu_sys_reg(vcpu, MDSCR_EL1));
>
> /*
> * HW Break/Watch points
> @@ -136,6 +174,9 @@ void kvm_arch_setup_debug(struct kvm_vcpu *vcpu)
> &host->dbg_wvr,
> sizeof(__u64)*nw);
>
> + if (trace_kvm_arch_setup_debug_reg32_enabled())
> + dump_dbg_regs(vcpu, nb, nw);
> +
> /* Make sure hyp.S copies them in/out */
> vcpu->arch.debug_flags |= KVM_ARM64_DEBUG_DIRTY;
> /* Also track guest changes */
> @@ -147,15 +188,24 @@ void kvm_arch_setup_debug(struct kvm_vcpu *vcpu)
> vcpu->arch.mdcr_el2 &= ~MDCR_EL2_TDE;
> }
>
> + trace_kvm_arch_setup_debug_reg32("MDCR_EL2", vcpu->arch.mdcr_el2);
> + trace_kvm_arch_setup_debug_reg32("MDSCR_EL1",
> + vcpu_sys_reg(vcpu, MDSCR_EL1));
> +
> +
> /* Trap debug register access? */
> if (trap_debug)
> vcpu->arch.mdcr_el2 |= MDCR_EL2_TDA;
> else
> vcpu->arch.mdcr_el2 &= ~MDCR_EL2_TDA;
> +
> + trace_kvm_arch_setup_debug_reg32("MDCR_EL2", vcpu->arch.mdcr_el2);
> }
>
> void kvm_arch_clear_debug(struct kvm_vcpu *vcpu)
> {
> + trace_kvm_arch_clear_debug(vcpu->guest_debug);
> +
> if (vcpu->guest_debug) {
> /* Restore pstate/mdscr bits we may have messed with */
> *vcpu_cpsr(vcpu) &= ~DBG_SPSR_SS;
> @@ -164,6 +214,8 @@ void kvm_arch_clear_debug(struct kvm_vcpu *vcpu)
> vcpu_sys_reg(vcpu, MDSCR_EL1) =
> vcpu_debug_saved_reg(vcpu, mdscr_el1);
>
> + trace_dreg("SPSR_EL2", *vcpu_cpsr(vcpu));
> + trace_dreg("MDSCR_EL1", vcpu_sys_reg(vcpu, MDSCR_EL1));
> /*
> * If we were using HW debug we need to restore the
> * values the guest had set them up with
> @@ -188,6 +240,10 @@ void kvm_arch_clear_debug(struct kvm_vcpu *vcpu)
> memcpy(&vcpu_sys_reg(vcpu, DBGWVR0_EL1),
> &regs->dbg_wvr,
> sizeof(__u64)*nw);
> +
> + if (trace_kvm_arch_setup_debug_reg32_enabled())
> + dump_dbg_regs(vcpu, nb, nw);
> +
> }
> }
> }
> diff --git a/arch/arm64/kvm/handle_exit.c b/arch/arm64/kvm/handle_exit.c
> index 460a1aa..c6cc69a 100644
> --- a/arch/arm64/kvm/handle_exit.c
> +++ b/arch/arm64/kvm/handle_exit.c
> @@ -97,6 +97,8 @@ static int kvm_handle_guest_debug(struct kvm_vcpu *vcpu, struct kvm_run *run)
> {
> u32 hsr = kvm_vcpu_get_hsr(vcpu);
>
> + trace_kvm_handle_guest_debug(*vcpu_pc(vcpu), hsr);
> +
> run->exit_reason = KVM_EXIT_DEBUG;
> run->debug.arch.hsr = hsr;
>
> diff --git a/arch/arm64/kvm/trace.h b/arch/arm64/kvm/trace.h
> index 157416e9..dffdb49 100644
> --- a/arch/arm64/kvm/trace.h
> +++ b/arch/arm64/kvm/trace.h
> @@ -44,6 +44,72 @@ TRACE_EVENT(kvm_hvc_arm64,
> __entry->vcpu_pc, __entry->r0, __entry->imm)
> );
>
> +TRACE_EVENT(kvm_handle_guest_debug,
> + TP_PROTO(unsigned long vcpu_pc, u32 hsr),
> + TP_ARGS(vcpu_pc, hsr),
> +
> + TP_STRUCT__entry(
> + __field(unsigned long, vcpu_pc)
> + __field(u32, hsr)
> + ),
> +
> + TP_fast_assign(
> + __entry->vcpu_pc = vcpu_pc;
> + __entry->hsr = hsr;
> + ),
> +
> + TP_printk("debug exception at 0x%08lx (HSR: 0x%08x)",
> + __entry->vcpu_pc, __entry->hsr)
> +);
> +
> +
> +TRACE_EVENT(kvm_arch_setup_debug,
> + TP_PROTO(__u32 guest_debug),
> + TP_ARGS(guest_debug),
> +
> + TP_STRUCT__entry(
> + __field(__u32, guest_debug)
> + ),
> +
> + TP_fast_assign(
> + __entry->guest_debug = guest_debug;
> + ),
> +
> + TP_printk("flags: 0x%08x", __entry->guest_debug)
> +);
> +
> +TRACE_EVENT(kvm_arch_clear_debug,
> + TP_PROTO(__u32 guest_debug),
> + TP_ARGS(guest_debug),
> +
> + TP_STRUCT__entry(
> + __field(__u32, guest_debug)
> + ),
> +
> + TP_fast_assign(
> + __entry->guest_debug = guest_debug;
> + ),
> +
> + TP_printk("flags: 0x%08x", __entry->guest_debug)
> +);
> +
> +TRACE_EVENT(kvm_arch_setup_debug_reg32,
> + TP_PROTO(const char *name, __u32 value),
> + TP_ARGS(name, value),
> +
> + TP_STRUCT__entry(
> + __field(const char *, name)
> + __field(__u32, value)
> + ),
> +
> + TP_fast_assign(
> + __entry->name = name;
> + __entry->value = value;
> + ),
> +
> + TP_printk("%s now 0x%08x", __entry->name, __entry->value)
> +);
> +
> #endif /* _TRACE_ARM64_KVM_H */
>
> #undef TRACE_INCLUDE_PATH
> --
> 2.3.4
>

I would guess that as far as merging any of this upstream keeping the
kvm_arch_set_debug() and kvm_handle_guest_debug() are worth keeping, but
only if the kvm_arch_set_debug() is only called when the guest is
actually being debugged from userspace.

Thanks,
-Christoffer