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Message-ID: <98c2210f-79dc-71d3-a684-a40fd419a388@loongson.cn>
Date: Thu, 12 Jan 2023 13:55:07 +0800
From: Jinyang He <hejinyang@...ngson.cn>
To: Huacai Chen <chenhuacai@...nel.org>
Cc: WANG Xuerui <kernel@...0n.name>,
Qing Zhang <zhangqing@...ngson.cn>, loongarch@...ts.linux.dev,
linux-kernel@...r.kernel.org, Steven Rostedt <rostedt@...dmis.org>,
Masami Hiramatsu <mhiramat@...nel.org>,
Mark Rutland <mark.rutland@....com>
Subject: Re: [PATCH v3 5/5] LoongArch: Add generic ex-handler unwind in
prologue unwinder
On 2023-01-12 08:59, Huacai Chen wrote:
> Hi, Jinyang,
>
> Have you tested this patch on NUMA systems? I don't say it cannot
> work, I just concern about it, because NUMA systems use different
> exception tables.
Sorry, I do not have machine except 3A5000. When CONFIG_NUMA is enabled,
the non-boot CPU sets its CSR.EENTRY values pcpu_handlers[cpu]. So I think
if CONFIG_NUMA is enabled, the other machines should perform as 3A5000
doing. (The boot CPU use eentry as the exception entry, and the non-boot
CPU use pcpu_handlers[cpu] as the exception entry). If that makes sense,
I think the patch will also work well on other NUMA machines.
Thanks,
Jinyang
>
> Huacai
>
> On Thu, Jan 12, 2023 at 8:41 AM Jinyang He <hejinyang@...ngson.cn> wrote:
>> When exception is triggered, code flow go handle_\exception in some
>> cases. One of stackframe in this case as follows,
>>
>> high -> +-------+
>> | REGS | <- a pt_regs
>> | |
>> | | <- ex trigger
>> | REGS | <- ex pt_regs <-+
>> | | |
>> | | |
>> low -> +-------+ ->unwind-+
>>
>> When unwinder unwind to handler_\exception it cannot go on prologue
>> analysis. It is asynchronous code flow, we should get the next frame
>> PC from regs->csr_era but not from regs->regs[1]. And we copy the
>> handler codes to eentry in the early time and copy the handler codes
>> to NUMA-relative memory named pcpu_handlers if NUMA is enabled. Thus,
>> unwinder cannot unwind normally. Therefore, try to give some hint in
>> handler_\exception and fixup it in unwind_next_frame.
>>
>> Reported-by: Qing Zhang <zhangqing@...ngson.cn>
>> Signed-off-by: Jinyang He <hejinyang@...ngson.cn>
>> ---
>> arch/loongarch/include/asm/unwind.h | 2 +-
>> arch/loongarch/kernel/genex.S | 3 +
>> arch/loongarch/kernel/unwind_prologue.c | 100 +++++++++++++++++++++---
>> arch/loongarch/mm/tlb.c | 2 +-
>> 4 files changed, 92 insertions(+), 15 deletions(-)
>>
>> diff --git a/arch/loongarch/include/asm/unwind.h b/arch/loongarch/include/asm/unwind.h
>> index cb428e1b19af..a38eb152aefb 100644
>> --- a/arch/loongarch/include/asm/unwind.h
>> +++ b/arch/loongarch/include/asm/unwind.h
>> @@ -22,7 +22,7 @@ struct unwind_state {
>> char type; /* UNWINDER_XXX */
>> struct stack_info stack_info;
>> struct task_struct *task;
>> - bool first, error, is_ftrace;
>> + bool first, error, reset;
>> int graph_idx;
>> unsigned long sp, pc, ra;
>> };
>> diff --git a/arch/loongarch/kernel/genex.S b/arch/loongarch/kernel/genex.S
>> index 75e5be807a0d..7e5c293ed89f 100644
>> --- a/arch/loongarch/kernel/genex.S
>> +++ b/arch/loongarch/kernel/genex.S
>> @@ -67,14 +67,17 @@ SYM_FUNC_END(except_vec_cex)
>> .macro BUILD_HANDLER exception handler prep
>> .align 5
>> SYM_FUNC_START(handle_\exception)
>> + 666:
>> BACKUP_T0T1
>> SAVE_ALL
>> build_prep_\prep
>> move a0, sp
>> la.abs t0, do_\handler
>> jirl ra, t0, 0
>> + 668:
>> RESTORE_ALL_AND_RET
>> SYM_FUNC_END(handle_\exception)
>> + SYM_DATA(unwind_hint_\exception, .word 668b - 666b)
>> .endm
>>
>> BUILD_HANDLER ade ade badv
>> diff --git a/arch/loongarch/kernel/unwind_prologue.c b/arch/loongarch/kernel/unwind_prologue.c
>> index e6c3f2ee507c..e52c18c2b604 100644
>> --- a/arch/loongarch/kernel/unwind_prologue.c
>> +++ b/arch/loongarch/kernel/unwind_prologue.c
>> @@ -2,21 +2,100 @@
>> /*
>> * Copyright (C) 2022 Loongson Technology Corporation Limited
>> */
>> +#include <linux/cpumask.h>
>> #include <linux/ftrace.h>
>> #include <linux/kallsyms.h>
>>
>> #include <asm/inst.h>
>> +#include <asm/loongson.h>
>> #include <asm/ptrace.h>
>> +#include <asm/setup.h>
>> #include <asm/unwind.h>
>>
>> -static inline void unwind_state_fixup(struct unwind_state *state)
>> +extern const int unwind_hint_ade;
>> +extern const int unwind_hint_ale;
>> +extern const int unwind_hint_bp;
>> +extern const int unwind_hint_fpe;
>> +extern const int unwind_hint_fpu;
>> +extern const int unwind_hint_lsx;
>> +extern const int unwind_hint_lasx;
>> +extern const int unwind_hint_lbt;
>> +extern const int unwind_hint_ri;
>> +extern const int unwind_hint_watch;
>> +extern unsigned long eentry;
>> +#ifdef CONFIG_NUMA
>> +extern unsigned long pcpu_handlers[NR_CPUS];
>> +#endif
>> +
>> +static inline bool scan_handler(unsigned long entry_offset)
>> {
>> -#ifdef CONFIG_DYNAMIC_FTRACE
>> - static unsigned long ftrace = (unsigned long)ftrace_call + 4;
>> + int idx, offset;
>>
>> - if (state->pc == ftrace)
>> - state->is_ftrace = true;
>> + if (entry_offset >= EXCCODE_INT_START * VECSIZE)
>> + return false;
>> +
>> + idx = entry_offset / VECSIZE;
>> + offset = entry_offset % VECSIZE;
>> + switch (idx) {
>> + case EXCCODE_ADE:
>> + return offset == unwind_hint_ade;
>> + case EXCCODE_ALE:
>> + return offset == unwind_hint_ale;
>> + case EXCCODE_BP:
>> + return offset == unwind_hint_bp;
>> + case EXCCODE_FPE:
>> + return offset == unwind_hint_fpe;
>> + case EXCCODE_FPDIS:
>> + return offset == unwind_hint_fpu;
>> + case EXCCODE_LSXDIS:
>> + return offset == unwind_hint_lsx;
>> + case EXCCODE_LASXDIS:
>> + return offset == unwind_hint_lasx;
>> + case EXCCODE_BTDIS:
>> + return offset == unwind_hint_lbt;
>> + case EXCCODE_INE:
>> + return offset == unwind_hint_ri;
>> + case EXCCODE_WATCH:
>> + return offset == unwind_hint_watch;
>> + default:
>> + return false;
>> + }
>> +}
>> +
>> +static inline bool fix_exceptions(unsigned long pc)
>> +{
>> +#ifdef CONFIG_NUMA
>> + int cpu;
>> +
>> + for_each_possible_cpu(cpu) {
>> + if (!pcpu_handlers[cpu])
>> + continue;
>> + if (scan_handler(pc - pcpu_handlers[cpu]))
>> + return true;
>> + }
>> #endif
>> + return scan_handler(pc - eentry);
>> +}
>> +
>> +/*
>> + * As we meet ftrace_regs_entry, reset first flag like first doing
>> + * tracing. Prologue analysis will stop soon because PC is at entry.
>> + */
>> +static inline bool fix_ftrace(unsigned long pc)
>> +{
>> +#ifdef CONFIG_DYNAMIC_FTRACE
>> + return pc == (unsigned long)ftrace_call + LOONGARCH_INSN_SIZE;
>> +#else
>> + return false;
>> +#endif
>> +}
>> +
>> +static inline bool unwind_state_fixup(struct unwind_state *state)
>> +{
>> + if (!fix_exceptions(state->pc) && !fix_ftrace(state->pc))
>> + return false;
>> + state->reset = true;
>> + return true;
>> }
>>
>> /*
>> @@ -39,14 +118,10 @@ static bool unwind_by_prologue(struct unwind_state *state)
>> if (state->sp >= info->end || state->sp < info->begin)
>> return false;
>>
>> - if (state->is_ftrace) {
>> - /*
>> - * As we meet ftrace_regs_entry, reset first flag like first doing
>> - * tracing. Prologue analysis will stop soon because PC is at entry.
>> - */
>> + if (state->reset) {
>> regs = (struct pt_regs *)state->sp;
>> state->first = true;
>> - state->is_ftrace = false;
>> + state->reset = false;
>> state->pc = regs->csr_era;
>> state->ra = regs->regs[1];
>> state->sp = regs->regs[3];
>> @@ -111,8 +186,7 @@ static bool unwind_by_prologue(struct unwind_state *state)
>>
>> out:
>> state->first = false;
>> - unwind_state_fixup(state);
>> - return !!__kernel_text_address(state->pc);
>> + return unwind_state_fixup(state) || __kernel_text_address(state->pc);
>> }
>>
>> static bool next_frame(struct unwind_state *state)
>> diff --git a/arch/loongarch/mm/tlb.c b/arch/loongarch/mm/tlb.c
>> index da3681f131c8..8bad6b0cff59 100644
>> --- a/arch/loongarch/mm/tlb.c
>> +++ b/arch/loongarch/mm/tlb.c
>> @@ -251,7 +251,7 @@ static void output_pgtable_bits_defines(void)
>> }
>>
>> #ifdef CONFIG_NUMA
>> -static unsigned long pcpu_handlers[NR_CPUS];
>> +unsigned long pcpu_handlers[NR_CPUS];
>> #endif
>> extern long exception_handlers[VECSIZE * 128 / sizeof(long)];
>>
>> --
>> 2.34.3
>>
>>
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