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

[Alex BennÃe]

Andrew Jones <drjones@xxxxxxxxxx> writes:

> $SUBJECT | sed s/guest_debug debug/guest debug/ ?
>
> On Tue, Mar 31, 2015 at 04:08:08PM +0100, Alex BennÃe 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 BennÃe <alex.bennee@xxxxxxxxxx>
>> 
>> 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)
>
> I don't think this name shortener should be necessary

Yeah it was just a quick hack as lower down the trace_ statements kept
wrapping and it looked ugly. I guess it would be less of an issue if I
shorten the setup/clear names.

>
>> +
>>  /* 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);
>
> Not using your trace_dreg here? I guess you didn't think it was
> necessary either.
>
>> +
>>  	/*
>>  	 * 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
>> 
>
> This looks like it would be super noisy. I'm sure that's nice for
> developing/debugging, but can't we reduce the, now debugged, version
> down to just one trace point per unique, and interesting, path? If you
> have several variables you want to see, then maybe they can all be
> on the same line.

Sure - I kept the multiple register references for debugging but your
right it can be compressed down now it's working.

>
> Also, I'm not sure about the necessity of the dump_dbg_regs function,
> but I think you should be able to embed it in the trace event code
> using __print_array

Thanks, I'll look at that.

>
> drew

-- 
Alex BennÃe
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