[PATCH v2] riscv: add tracepoints for page fault

[Zhu Hengbo]

On 2024/7/20 18:18, Jisheng Zhang wrote:
> On Wed, Jul 17, 2024 at 08:27:19AM +0000, Zhu Hengbo wrote:
>> Introduce page_fault_user and page_fault_kernel for riscv page fault.
>> Help to get more detail information when page fault happen.
> Just curious what's the expected usage? The mm subsystem has supported
> page faults perf software event, is it enough?


I think there will still be situations where we need to use debugfs for debugging in cases where perf is not available.

In fact, I am working to achieve parity in functionality for RISC-V with x86 and ARM.
In x86, there are both perf software events and tracepoints.


>> Signed-off-by: Zhu Hengbo <zhuhengbo at iscas.ac.cn>
>> ---
>> Changes in v2:
>> - Add print instruction point info
>>
>> Simple test go below:
>>
>> root at riscv-ubuntu2204 ~ # bin/perf list | grep exceptions
>>   exceptions:page_fault_kernel                       [Tracepoint event]
>>   exceptions:page_fault_user                         [Tracepoint event]
>>
>> root at riscv-ubuntu2204 ~ # bin/perf record -e exceptions:page_fault_kernel -e exceptions:page_fault_user
>> [ perf record: Woken up 1 times to write data ]
>> [ perf record: Captured and wrote 0.091 MB perf.data (19 samples) ]
>>
>> perf report tracepoint:
>> perf     563 [007]   115.824363:   exceptions:page_fault_user: user page fault, address=0x7fff94cf6400 epc=0x55558632808e cause=0xd
>> perf     563 [007]   115.824441:   exceptions:page_fault_user: user page fault, address=0x7fff94c75400 epc=0x55558632808e cause=0xd
>> perf     563 [007]   115.824518:   exceptions:page_fault_user: user page fault, address=0x7fff94bf4400 epc=0x55558632808e cause=0xd
>> perf     563 [007]   115.824907: exceptions:page_fault_kernel: kernel page fault, address=0x7fff94bf5000 epc=fault_in_readable cause=0xd
>> perf     563 [007]   115.825238:   exceptions:page_fault_user: user page fault, address=0x7fff94bf4408 epc=0x5555863281bc cause=0xf
>> perf     564 [000]   116.247999:   exceptions:page_fault_user: user page fault, address=0x7fff94b73400 epc=0x55558632808e cause=0xd
>> perf     564 [000]   116.248558:   exceptions:page_fault_user: user page fault, address=0x7fff94af2400 epc=0x55558632808e cause=0xd
>> ---
>>  arch/riscv/include/asm/trace/exceptions.h | 66 +++++++++++++++++++++++
>>  arch/riscv/mm/fault.c                     | 15 ++++++
>>  2 files changed, 81 insertions(+)
>>  create mode 100644 arch/riscv/include/asm/trace/exceptions.h
>>
>> diff --git a/arch/riscv/include/asm/trace/exceptions.h b/arch/riscv/include/asm/trace/exceptions.h
>> new file mode 100644
>> index 000000000000..ff258da2f45f
>> --- /dev/null
>> +++ b/arch/riscv/include/asm/trace/exceptions.h
>> @@ -0,0 +1,66 @@
>> +/* SPDX-License-Identifier: GPL-2.0 */
>> +/*
>> + * Tracepoints for RISC-V exceptions
>> + *
>> + * Copyright (C) 2024 ISCAS. All rights reserved
>> + *
>> + */
>> +
>> +#if !defined(_TRACE_PAGE_FAULT_H) || defined(TRACE_HEADER_MULTI_READ)
>> +#define _TRACE_PAGE_FAULT_H
>> +
>> +#include <linux/tracepoint.h>
>> +
>> +#undef TRACE_SYSTEM
>> +#define TRACE_SYSTEM exceptions
>> +
>> +TRACE_EVENT(page_fault_user,
>> +	TP_PROTO(struct pt_regs *regs),
>> +	TP_ARGS(regs),
>> +
>> +	TP_STRUCT__entry(
>> +		__field(unsigned long, address)
>> +		__field(unsigned long, epc)
>> +		__field(unsigned long, cause)
>> +	),
>> +
>> +	TP_fast_assign(
>> +		__entry->address	= regs->badaddr;
>> +		__entry->epc		= regs->epc;
>> +		__entry->cause		= regs->cause;
>> +	),
>> +
>> +	TP_printk("user page fault, address=%ps epc=%ps cause=0x%lx",
>> +			(void *)__entry->address, (void *)__entry->epc,
>> +			__entry->cause)
>> +);
>> +
>> +TRACE_EVENT(page_fault_kernel,
>> +	TP_PROTO(struct pt_regs *regs),
>> +	TP_ARGS(regs),
>> +
>> +	TP_STRUCT__entry(
>> +		__field(unsigned long, address)
>> +		__field(unsigned long, epc)
>> +		__field(unsigned long, cause)
>> +	),
>> +
>> +	TP_fast_assign(
>> +		__entry->address	= regs->badaddr;
>> +		__entry->epc		= regs->epc;
>> +		__entry->cause		= regs->cause;
>> +	),
>> +
>> +	TP_printk("kernel page fault, address=%ps epc=%ps cause=0x%lx",
>> +			(void *)__entry->address, (void *)__entry->epc,
>> +			__entry->cause)
>> +);
>> +
>> +#undef TRACE_INCLUDE_PATH
>> +#undef TRACE_INCLUDE_FILE
>> +#define TRACE_INCLUDE_PATH asm/trace/
>> +#define TRACE_INCLUDE_FILE exceptions
>> +#endif /*  _TRACE_PAGE_FAULT_H */
>> +
>> +/* This part must be outside protection */
>> +#include <trace/define_trace.h>
>> diff --git a/arch/riscv/mm/fault.c b/arch/riscv/mm/fault.c
>> index 5224f3733802..22874074c5bc 100644
>> --- a/arch/riscv/mm/fault.c
>> +++ b/arch/riscv/mm/fault.c
>> @@ -22,6 +22,10 @@
>>  
>>  #include "../kernel/head.h"
>>  
>> +
>> +#define CREATE_TRACE_POINTS
>> +#include <asm/trace/exceptions.h>
>> +
>>  static void die_kernel_fault(const char *msg, unsigned long addr,
>>  		struct pt_regs *regs)
>>  {
>> @@ -215,6 +219,15 @@ static inline bool access_error(unsigned long cause, struct vm_area_struct *vma)
>>  	return false;
>>  }
>>  
>> +
>> +static inline void trace_page_fault(struct pt_regs *regs)
>> +{
>> +	if (user_mode(regs))
>> +		trace_page_fault_user(regs);
>> +	else
>> +		trace_page_fault_kernel(regs);
>> +}
>> +
>>  /*
>>   * This routine handles page faults.  It determines the address and the
>>   * problem, and then passes it off to one of the appropriate routines.
>> @@ -235,6 +248,8 @@ void handle_page_fault(struct pt_regs *regs)
>>  	tsk = current;
>>  	mm = tsk->mm;
>>  
>> +	trace_page_fault(regs);
>> +
>>  	if (kprobe_page_fault(regs, cause))
>>  		return;
>>  
>> -- 
>> 2.34.1
>>
>>
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