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[59.124.168.89]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-70803ecfb90sm1377775b3a.139.2024.06.28.04.48.13 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 28 Jun 2024 04:48:17 -0700 (PDT) From: Andy Chiu Date: Fri, 28 Jun 2024 19:47:44 +0800 Subject: [PATCH v2 1/6] riscv: ftrace: support fastcc in Clang for WITH_ARGS Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Message-Id: <20240628-dev-andyc-dyn-ftrace-v4-v2-1-1e5f4cb1f049@sifive.com> References: <20240628-dev-andyc-dyn-ftrace-v4-v2-0-1e5f4cb1f049@sifive.com> In-Reply-To: <20240628-dev-andyc-dyn-ftrace-v4-v2-0-1e5f4cb1f049@sifive.com> To: Paul Walmsley , Palmer Dabbelt , Albert Ou , Alexandre Ghiti , Zong Li , Steven Rostedt , Masami Hiramatsu , Mark Rutland , Nathan Chancellor , Nick Desaulniers , Bill Wendling , Justin Stitt , Puranjay Mohan Cc: Palmer Dabbelt , linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, llvm@lists.linux.dev, Evgenii Shatokhin , Andy Chiu X-Mailer: b4 0.12.4 Some caller-saved registers which are not defined as function arguments in the ABI can still be passed as arguments when the kernel is compiled with Clang. As a result, we must save and restore those registers to prevent ftrace from clobbering them. - [1]: https://reviews.llvm.org/D68559 Reported-by: Evgenii Shatokhin Closes: https://lore.kernel.org/linux-riscv/7e7c7914-445d-426d-89a0-59a9199c45b1@yadro.com/ Acked-by: Nathan Chancellor Signed-off-by: Andy Chiu --- arch/riscv/include/asm/ftrace.h | 7 +++++++ arch/riscv/kernel/asm-offsets.c | 7 +++++++ arch/riscv/kernel/mcount-dyn.S | 16 ++++++++++++++-- 3 files changed, 28 insertions(+), 2 deletions(-) diff --git a/arch/riscv/include/asm/ftrace.h b/arch/riscv/include/asm/ftrace.h index 9eb31a7ea0aa..5f81c53dbfd9 100644 --- a/arch/riscv/include/asm/ftrace.h +++ b/arch/riscv/include/asm/ftrace.h @@ -144,6 +144,13 @@ struct ftrace_regs { unsigned long a5; unsigned long a6; unsigned long a7; +#ifdef CONFIG_CC_IS_CLANG + unsigned long t2; + unsigned long t3; + unsigned long t4; + unsigned long t5; + unsigned long t6; +#endif }; }; }; diff --git a/arch/riscv/kernel/asm-offsets.c b/arch/riscv/kernel/asm-offsets.c index b09ca5f944f7..db5a26fcc9ae 100644 --- a/arch/riscv/kernel/asm-offsets.c +++ b/arch/riscv/kernel/asm-offsets.c @@ -497,6 +497,13 @@ void asm_offsets(void) DEFINE(FREGS_SP, offsetof(struct ftrace_regs, sp)); DEFINE(FREGS_S0, offsetof(struct ftrace_regs, s0)); DEFINE(FREGS_T1, offsetof(struct ftrace_regs, t1)); +#ifdef CONFIG_CC_IS_CLANG + DEFINE(FREGS_T2, offsetof(struct ftrace_regs, t2)); + DEFINE(FREGS_T3, offsetof(struct ftrace_regs, t3)); + DEFINE(FREGS_T4, offsetof(struct ftrace_regs, t4)); + DEFINE(FREGS_T5, offsetof(struct ftrace_regs, t5)); + DEFINE(FREGS_T6, offsetof(struct ftrace_regs, t6)); +#endif DEFINE(FREGS_A0, offsetof(struct ftrace_regs, a0)); DEFINE(FREGS_A1, offsetof(struct ftrace_regs, a1)); DEFINE(FREGS_A2, offsetof(struct ftrace_regs, a2)); diff --git a/arch/riscv/kernel/mcount-dyn.S b/arch/riscv/kernel/mcount-dyn.S index 745dd4c4a69c..e988bd26b28b 100644 --- a/arch/riscv/kernel/mcount-dyn.S +++ b/arch/riscv/kernel/mcount-dyn.S @@ -96,7 +96,13 @@ REG_S x8, FREGS_S0(sp) #endif REG_S x6, FREGS_T1(sp) - +#ifdef CONFIG_CC_IS_CLANG + REG_S x7, FREGS_T2(sp) + REG_S x28, FREGS_T3(sp) + REG_S x29, FREGS_T4(sp) + REG_S x30, FREGS_T5(sp) + REG_S x31, FREGS_T6(sp) +#endif // save the arguments REG_S x10, FREGS_A0(sp) REG_S x11, FREGS_A1(sp) @@ -115,7 +121,13 @@ REG_L x8, FREGS_S0(sp) #endif REG_L x6, FREGS_T1(sp) - +#ifdef CONFIG_CC_IS_CLANG + REG_L x7, FREGS_T2(sp) + REG_L x28, FREGS_T3(sp) + REG_L x29, FREGS_T4(sp) + REG_L x30, FREGS_T5(sp) + REG_L x31, FREGS_T6(sp) +#endif // restore the arguments REG_L x10, FREGS_A0(sp) REG_L x11, FREGS_A1(sp) From patchwork Fri Jun 28 11:47:45 2024 Content-Type: text/plain; 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[59.124.168.89]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-70803ecfb90sm1377775b3a.139.2024.06.28.04.48.17 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 28 Jun 2024 04:48:21 -0700 (PDT) From: Andy Chiu Date: Fri, 28 Jun 2024 19:47:45 +0800 Subject: [PATCH v2 2/6] riscv: ftrace: align patchable functions to 4 Byte boundary Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Message-Id: <20240628-dev-andyc-dyn-ftrace-v4-v2-2-1e5f4cb1f049@sifive.com> References: <20240628-dev-andyc-dyn-ftrace-v4-v2-0-1e5f4cb1f049@sifive.com> In-Reply-To: <20240628-dev-andyc-dyn-ftrace-v4-v2-0-1e5f4cb1f049@sifive.com> To: Paul Walmsley , Palmer Dabbelt , Albert Ou , Alexandre Ghiti , Zong Li , Steven Rostedt , Masami Hiramatsu , Mark Rutland , Nathan Chancellor , Nick Desaulniers , Bill Wendling , Justin Stitt , Puranjay Mohan Cc: Palmer Dabbelt , linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, llvm@lists.linux.dev, Evgenii Shatokhin , Andy Chiu X-Mailer: b4 0.12.4 We are changing ftrace code patching in order to remove dependency from stop_machine() and enable kernel preemption. This requires us to align functions entry at a 4-B align address. However, -falign-functions on older versions of GCC alone was not strong enoungh to align all functions. In fact, cold functions are not aligned after turning on optimizations. We consider this is a bug in GCC and turn off guess-branch-probility as a workaround to align all functions. GCC bug id: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88345 The option -fmin-function-alignment is able to align all functions properly on newer versions of gcc. So, we add a cc-option to test if the toolchain supports it. Suggested-by: Evgenii Shatokhin Signed-off-by: Andy Chiu Reviewed-by: Björn Töpel --- Changelog v2: - Use CC_HAS_MIN_FUNCTION_ALIGNMENT and it friends to prevent reinventing wheels (Nathan) --- arch/riscv/Kconfig | 2 ++ 1 file changed, 2 insertions(+) diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig index 704d4683bcfa..55c70efbad0a 100644 --- a/arch/riscv/Kconfig +++ b/arch/riscv/Kconfig @@ -133,6 +133,7 @@ config RISCV select HAVE_DEBUG_KMEMLEAK select HAVE_DMA_CONTIGUOUS if MMU select HAVE_DYNAMIC_FTRACE if !XIP_KERNEL && MMU && (CLANG_SUPPORTS_DYNAMIC_FTRACE || GCC_SUPPORTS_DYNAMIC_FTRACE) + select FUNCTION_ALIGNMENT_4B if HAVE_DYNAMIC_FTRACE && RISCV_ISA_C select HAVE_DYNAMIC_FTRACE_WITH_DIRECT_CALLS select HAVE_DYNAMIC_FTRACE_WITH_ARGS if HAVE_DYNAMIC_FTRACE select HAVE_FTRACE_MCOUNT_RECORD if !XIP_KERNEL @@ -208,6 +209,7 @@ config CLANG_SUPPORTS_DYNAMIC_FTRACE config GCC_SUPPORTS_DYNAMIC_FTRACE def_bool CC_IS_GCC depends on $(cc-option,-fpatchable-function-entry=8) + depends on CC_HAS_MIN_FUNCTION_ALIGNMENT || !RISCV_ISA_C config HAVE_SHADOW_CALL_STACK def_bool $(cc-option,-fsanitize=shadow-call-stack) From patchwork Fri Jun 28 11:47:46 2024 Content-Type: text/plain; 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[59.124.168.89]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-70803ecfb90sm1377775b3a.139.2024.06.28.04.48.22 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 28 Jun 2024 04:48:25 -0700 (PDT) From: Andy Chiu Date: Fri, 28 Jun 2024 19:47:46 +0800 Subject: [PATCH v2 3/6] riscv: ftrace: prepare ftrace for atomic code patching Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Message-Id: <20240628-dev-andyc-dyn-ftrace-v4-v2-3-1e5f4cb1f049@sifive.com> References: <20240628-dev-andyc-dyn-ftrace-v4-v2-0-1e5f4cb1f049@sifive.com> In-Reply-To: <20240628-dev-andyc-dyn-ftrace-v4-v2-0-1e5f4cb1f049@sifive.com> To: Paul Walmsley , Palmer Dabbelt , Albert Ou , Alexandre Ghiti , Zong Li , Steven Rostedt , Masami Hiramatsu , Mark Rutland , Nathan Chancellor , Nick Desaulniers , Bill Wendling , Justin Stitt , Puranjay Mohan Cc: Palmer Dabbelt , linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, llvm@lists.linux.dev, Andy Chiu X-Mailer: b4 0.12.4 We use an AUIPC+JALR pair to jump into a ftrace trampoline. Since instruction fetch can break down to 4 byte at a time, it is impossible to update two instructions without a race. In order to mitigate it, we initialize the patchable entry to AUIPC + NOP4. Then, the run-time code patching can change NOP4 to JALR to eable/disable ftrcae from a function. This limits the reach of each ftrace entry to +-2KB displacing from ftrace_caller. Starting from the trampoline, we add a level of indirection for it to reach ftrace caller target. Now, it loads the target address from a memory location, then perform the jump. This enable the kernel to update the target atomically. The ordering of reading/updating the targert address should be guarded by generic ftrace code, where it sends smp_rmb ipi. Signed-off-by: Andy Chiu --- arch/riscv/include/asm/ftrace.h | 4 +++ arch/riscv/kernel/ftrace.c | 80 ++++++++++++++++++++++++++--------------- arch/riscv/kernel/mcount-dyn.S | 9 +++-- 3 files changed, 62 insertions(+), 31 deletions(-) diff --git a/arch/riscv/include/asm/ftrace.h b/arch/riscv/include/asm/ftrace.h index 5f81c53dbfd9..7199383f8c02 100644 --- a/arch/riscv/include/asm/ftrace.h +++ b/arch/riscv/include/asm/ftrace.h @@ -81,6 +81,7 @@ struct dyn_arch_ftrace { #define JALR_T0 (0x000282e7) #define AUIPC_T0 (0x00000297) #define NOP4 (0x00000013) +#define JALR_RANGE (JALR_SIGN_MASK - 1) #define to_jalr_t0(offset) \ (((offset & JALR_OFFSET_MASK) << JALR_SHIFT) | JALR_T0) @@ -118,6 +119,9 @@ do { \ * Let auipc+jalr be the basic *mcount unit*, so we make it 8 bytes here. */ #define MCOUNT_INSN_SIZE 8 +#define MCOUNT_AUIPC_SIZE 4 +#define MCOUNT_JALR_SIZE 4 +#define MCOUNT_NOP4_SIZE 4 #ifndef __ASSEMBLY__ struct dyn_ftrace; diff --git a/arch/riscv/kernel/ftrace.c b/arch/riscv/kernel/ftrace.c index 4b95c574fd04..5ebe412280ef 100644 --- a/arch/riscv/kernel/ftrace.c +++ b/arch/riscv/kernel/ftrace.c @@ -64,42 +64,64 @@ static int ftrace_check_current_call(unsigned long hook_pos, return 0; } -static int __ftrace_modify_call(unsigned long hook_pos, unsigned long target, - bool enable, bool ra) +static int __ftrace_modify_call(unsigned long hook_pos, unsigned long target, bool validate) { unsigned int call[2]; - unsigned int nops[2] = {NOP4, NOP4}; + unsigned int replaced[2]; + + make_call_t0(hook_pos, target, call); - if (ra) - make_call_ra(hook_pos, target, call); - else - make_call_t0(hook_pos, target, call); + if (validate) { + /* + * Read the text we want to modify; + * return must be -EFAULT on read error + */ + if (copy_from_kernel_nofault(replaced, (void *)hook_pos, + MCOUNT_INSN_SIZE)) + return -EFAULT; + + if (replaced[0] != call[0]) { + pr_err("%p: expected (%08x) but got (%08x)\n", + (void *)hook_pos, call[0], replaced[0]); + return -EINVAL; + } + } - /* Replace the auipc-jalr pair at once. Return -EPERM on write error. */ - if (patch_insn_write((void *)hook_pos, enable ? call : nops, MCOUNT_INSN_SIZE)) + /* Replace the jalr at once. Return -EPERM on write error. */ + if (patch_insn_write((void *)(hook_pos + MCOUNT_AUIPC_SIZE), call + 1, MCOUNT_JALR_SIZE)) return -EPERM; return 0; } -int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr) +static int __ftrace_modify_call_site(ftrace_func_t *hook_pos, ftrace_func_t target, bool enable) { - unsigned int call[2]; + ftrace_func_t call = target; + ftrace_func_t nops = &ftrace_stub; - make_call_t0(rec->ip, addr, call); - - if (patch_insn_write((void *)rec->ip, call, MCOUNT_INSN_SIZE)) - return -EPERM; + WRITE_ONCE(*hook_pos, enable ? call : nops); return 0; } +int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr) +{ + unsigned long distance, orig_addr; + + orig_addr = (unsigned long)&ftrace_caller; + distance = addr > orig_addr ? addr - orig_addr : orig_addr - addr; + if (distance > JALR_RANGE) + return -EINVAL; + + return __ftrace_modify_call(rec->ip, addr, false); +} + int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec, unsigned long addr) { - unsigned int nops[2] = {NOP4, NOP4}; + unsigned int nops[1] = {NOP4}; - if (patch_insn_write((void *)rec->ip, nops, MCOUNT_INSN_SIZE)) + if (patch_insn_write((void *)(rec->ip + MCOUNT_AUIPC_SIZE), nops, MCOUNT_NOP4_SIZE)) return -EPERM; return 0; @@ -114,21 +136,23 @@ int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec, */ int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec) { + unsigned int nops[2]; int out; + make_call_t0(rec->ip, &ftrace_caller, nops); + nops[1] = NOP4; + mutex_lock(&text_mutex); - out = ftrace_make_nop(mod, rec, MCOUNT_ADDR); + out = patch_insn_write((void *)rec->ip, nops, MCOUNT_INSN_SIZE); mutex_unlock(&text_mutex); return out; } +ftrace_func_t ftrace_call_dest = ftrace_stub; int ftrace_update_ftrace_func(ftrace_func_t func) { - int ret = __ftrace_modify_call((unsigned long)&ftrace_call, - (unsigned long)func, true, true); - - return ret; + return __ftrace_modify_call_site(&ftrace_call_dest, func, true); } struct ftrace_modify_param { @@ -182,7 +206,7 @@ int ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr, if (ret) return ret; - return __ftrace_modify_call(caller, addr, true, false); + return __ftrace_modify_call(caller, addr, true); } #endif @@ -217,17 +241,17 @@ void ftrace_graph_func(unsigned long ip, unsigned long parent_ip, prepare_ftrace_return(&fregs->ra, ip, fregs->s0); } #else /* CONFIG_DYNAMIC_FTRACE_WITH_ARGS */ -extern void ftrace_graph_call(void); +ftrace_func_t ftrace_graph_call_dest = ftrace_stub; int ftrace_enable_ftrace_graph_caller(void) { - return __ftrace_modify_call((unsigned long)&ftrace_graph_call, - (unsigned long)&prepare_ftrace_return, true, true); + return __ftrace_modify_call_site(&ftrace_graph_call_dest, + &prepare_ftrace_return, true); } int ftrace_disable_ftrace_graph_caller(void) { - return __ftrace_modify_call((unsigned long)&ftrace_graph_call, - (unsigned long)&prepare_ftrace_return, false, true); + return __ftrace_modify_call_site(&ftrace_graph_call_dest, + &prepare_ftrace_return, false); } #endif /* CONFIG_DYNAMIC_FTRACE_WITH_ARGS */ #endif /* CONFIG_DYNAMIC_FTRACE */ diff --git a/arch/riscv/kernel/mcount-dyn.S b/arch/riscv/kernel/mcount-dyn.S index e988bd26b28b..bc06e8ab81cf 100644 --- a/arch/riscv/kernel/mcount-dyn.S +++ b/arch/riscv/kernel/mcount-dyn.S @@ -162,7 +162,8 @@ SYM_FUNC_START(ftrace_caller) mv a3, sp SYM_INNER_LABEL(ftrace_call, SYM_L_GLOBAL) - call ftrace_stub + REG_L ra, ftrace_call_dest + jalr 0(ra) #ifdef CONFIG_FUNCTION_GRAPH_TRACER addi a0, sp, ABI_RA @@ -172,7 +173,8 @@ SYM_INNER_LABEL(ftrace_call, SYM_L_GLOBAL) mv a2, s0 #endif SYM_INNER_LABEL(ftrace_graph_call, SYM_L_GLOBAL) - call ftrace_stub + REG_L ra, ftrace_graph_call_dest + jalr 0(ra) #endif RESTORE_ABI jr t0 @@ -185,7 +187,8 @@ SYM_FUNC_START(ftrace_caller) PREPARE_ARGS SYM_INNER_LABEL(ftrace_call, SYM_L_GLOBAL) - call ftrace_stub + REG_L ra, ftrace_call_dest + jalr 0(ra) RESTORE_ABI_REGS bnez t1, .Ldirect From patchwork Fri Jun 28 11:47:47 2024 Content-Type: text/plain; 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[59.124.168.89]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-70803ecfb90sm1377775b3a.139.2024.06.28.04.48.26 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 28 Jun 2024 04:48:30 -0700 (PDT) From: Andy Chiu Date: Fri, 28 Jun 2024 19:47:47 +0800 Subject: [PATCH v2 4/6] riscv: ftrace: do not use stop_machine to update code Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Message-Id: <20240628-dev-andyc-dyn-ftrace-v4-v2-4-1e5f4cb1f049@sifive.com> References: <20240628-dev-andyc-dyn-ftrace-v4-v2-0-1e5f4cb1f049@sifive.com> In-Reply-To: <20240628-dev-andyc-dyn-ftrace-v4-v2-0-1e5f4cb1f049@sifive.com> To: Paul Walmsley , Palmer Dabbelt , Albert Ou , Alexandre Ghiti , Zong Li , Steven Rostedt , Masami Hiramatsu , Mark Rutland , Nathan Chancellor , Nick Desaulniers , Bill Wendling , Justin Stitt , Puranjay Mohan Cc: Palmer Dabbelt , linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, llvm@lists.linux.dev, Andy Chiu X-Mailer: b4 0.12.4 Now it is safe to remove dependency from stop_machine() for us to patch code in ftrace. Signed-off-by: Andy Chiu --- arch/riscv/kernel/ftrace.c | 53 ++++------------------------------------------ 1 file changed, 4 insertions(+), 49 deletions(-) diff --git a/arch/riscv/kernel/ftrace.c b/arch/riscv/kernel/ftrace.c index 5ebe412280ef..57a6558e212e 100644 --- a/arch/riscv/kernel/ftrace.c +++ b/arch/riscv/kernel/ftrace.c @@ -13,23 +13,13 @@ #include #ifdef CONFIG_DYNAMIC_FTRACE -void ftrace_arch_code_modify_prepare(void) __acquires(&text_mutex) +void arch_ftrace_update_code(int command) { mutex_lock(&text_mutex); - - /* - * The code sequences we use for ftrace can't be patched while the - * kernel is running, so we need to use stop_machine() to modify them - * for now. This doesn't play nice with text_mutex, we use this flag - * to elide the check. - */ - riscv_patch_in_stop_machine = true; -} - -void ftrace_arch_code_modify_post_process(void) __releases(&text_mutex) -{ - riscv_patch_in_stop_machine = false; + command |= FTRACE_MAY_SLEEP; + ftrace_modify_all_code(command); mutex_unlock(&text_mutex); + flush_icache_all(); } static int ftrace_check_current_call(unsigned long hook_pos, @@ -155,41 +145,6 @@ int ftrace_update_ftrace_func(ftrace_func_t func) return __ftrace_modify_call_site(&ftrace_call_dest, func, true); } -struct ftrace_modify_param { - int command; - atomic_t cpu_count; -}; - -static int __ftrace_modify_code(void *data) -{ - struct ftrace_modify_param *param = data; - - if (atomic_inc_return(¶m->cpu_count) == num_online_cpus()) { - ftrace_modify_all_code(param->command); - /* - * Make sure the patching store is effective *before* we - * increment the counter which releases all waiting CPUs - * by using the release variant of atomic increment. 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[59.124.168.89]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-70803ecfb90sm1377775b3a.139.2024.06.28.04.48.30 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 28 Jun 2024 04:48:34 -0700 (PDT) From: Andy Chiu Date: Fri, 28 Jun 2024 19:47:48 +0800 Subject: [PATCH v2 5/6] riscv: vector: Support calling schedule() for preemptible Vector Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Message-Id: <20240628-dev-andyc-dyn-ftrace-v4-v2-5-1e5f4cb1f049@sifive.com> References: <20240628-dev-andyc-dyn-ftrace-v4-v2-0-1e5f4cb1f049@sifive.com> In-Reply-To: <20240628-dev-andyc-dyn-ftrace-v4-v2-0-1e5f4cb1f049@sifive.com> To: Paul Walmsley , Palmer Dabbelt , Albert Ou , Alexandre Ghiti , Zong Li , Steven Rostedt , Masami Hiramatsu , Mark Rutland , Nathan Chancellor , Nick Desaulniers , Bill Wendling , Justin Stitt , Puranjay Mohan Cc: Palmer Dabbelt , linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, llvm@lists.linux.dev, Andy Chiu X-Mailer: b4 0.12.4 Each function entry implies a call to ftrace infrastructure. And it may call into schedule in some cases. So, it is possible for preemptible kernel-mode Vector to implicitly call into schedule. Since all V-regs are caller-saved, it is possible to drop all V context when a thread voluntarily call schedule(). Besides, we currently don't pass argument through vector register, so we don't have to save/restore V-regs in ftrace trampoline. Signed-off-by: Andy Chiu --- arch/riscv/include/asm/processor.h | 5 +++++ arch/riscv/include/asm/vector.h | 22 +++++++++++++++++++--- 2 files changed, 24 insertions(+), 3 deletions(-) diff --git a/arch/riscv/include/asm/processor.h b/arch/riscv/include/asm/processor.h index 68c3432dc6ea..02598e168659 100644 --- a/arch/riscv/include/asm/processor.h +++ b/arch/riscv/include/asm/processor.h @@ -95,6 +95,10 @@ struct pt_regs; * Thus, the task does not own preempt_v. Any use of Vector will have to * save preempt_v, if dirty, and fallback to non-preemptible kernel-mode * Vector. + * - bit 29: The thread voluntarily calls schedule() while holding an active + * preempt_v. All preempt_v context should be dropped in such case because + * V-regs are caller-saved. Only sstatus.VS=ON is persisted across a + * schedule() call. * - bit 30: The in-kernel preempt_v context is saved, and requries to be * restored when returning to the context that owns the preempt_v. * - bit 31: The in-kernel preempt_v context is dirty, as signaled by the @@ -109,6 +113,7 @@ struct pt_regs; #define RISCV_PREEMPT_V 0x00000100 #define RISCV_PREEMPT_V_DIRTY 0x80000000 #define RISCV_PREEMPT_V_NEED_RESTORE 0x40000000 +#define RISCV_PREEMPT_V_IN_SCHEDULE 0x20000000 /* CPU-specific state of a task */ struct thread_struct { diff --git a/arch/riscv/include/asm/vector.h b/arch/riscv/include/asm/vector.h index be7d309cca8a..fbf17aba92c1 100644 --- a/arch/riscv/include/asm/vector.h +++ b/arch/riscv/include/asm/vector.h @@ -75,6 +75,11 @@ static __always_inline void riscv_v_disable(void) csr_clear(CSR_SSTATUS, SR_VS); } +static __always_inline bool riscv_v_is_on(void) +{ + return !!(csr_read(CSR_SSTATUS) & SR_VS); +} + static __always_inline void __vstate_csr_save(struct __riscv_v_ext_state *dest) { asm volatile ( @@ -243,6 +248,11 @@ static inline void __switch_to_vector(struct task_struct *prev, struct pt_regs *regs; if (riscv_preempt_v_started(prev)) { + if (riscv_v_is_on()) { + WARN_ON(prev->thread.riscv_v_flags & RISCV_V_CTX_DEPTH_MASK); + riscv_v_disable(); + prev->thread.riscv_v_flags |= RISCV_PREEMPT_V_IN_SCHEDULE; + } if (riscv_preempt_v_dirty(prev)) { __riscv_v_vstate_save(&prev->thread.kernel_vstate, prev->thread.kernel_vstate.datap); @@ -253,10 +263,16 @@ static inline void __switch_to_vector(struct task_struct *prev, riscv_v_vstate_save(&prev->thread.vstate, regs); } - if (riscv_preempt_v_started(next)) - riscv_preempt_v_set_restore(next); - else + if (riscv_preempt_v_started(next)) { + if (next->thread.riscv_v_flags & RISCV_PREEMPT_V_IN_SCHEDULE) { + next->thread.riscv_v_flags &= ~RISCV_PREEMPT_V_IN_SCHEDULE; + riscv_v_enable(); + } else { + riscv_preempt_v_set_restore(next); + } + } else { riscv_v_vstate_set_restore(next, task_pt_regs(next)); + } } void riscv_v_vstate_ctrl_init(struct task_struct *tsk); From patchwork Fri Jun 28 11:47:49 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Andy Chiu X-Patchwork-Id: 13715996 Received: from mail-oa1-f43.google.com (mail-oa1-f43.google.com [209.85.160.43]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 837BF158DAC for ; 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[59.124.168.89]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-70803ecfb90sm1377775b3a.139.2024.06.28.04.48.34 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 28 Jun 2024 04:48:38 -0700 (PDT) From: Andy Chiu Date: Fri, 28 Jun 2024 19:47:49 +0800 Subject: [PATCH v2 6/6] riscv: ftrace: support PREEMPT Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Message-Id: <20240628-dev-andyc-dyn-ftrace-v4-v2-6-1e5f4cb1f049@sifive.com> References: <20240628-dev-andyc-dyn-ftrace-v4-v2-0-1e5f4cb1f049@sifive.com> In-Reply-To: <20240628-dev-andyc-dyn-ftrace-v4-v2-0-1e5f4cb1f049@sifive.com> To: Paul Walmsley , Palmer Dabbelt , Albert Ou , Alexandre Ghiti , Zong Li , Steven Rostedt , Masami Hiramatsu , Mark Rutland , Nathan Chancellor , Nick Desaulniers , Bill Wendling , Justin Stitt , Puranjay Mohan Cc: Palmer Dabbelt , linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, llvm@lists.linux.dev, Andy Chiu X-Mailer: b4 0.12.4 Now, we can safely enable dynamic ftrace with kernel preemption. Signed-off-by: Andy Chiu --- arch/riscv/Kconfig | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig index 55c70efbad0a..881ea466ff52 100644 --- a/arch/riscv/Kconfig +++ b/arch/riscv/Kconfig @@ -139,7 +139,7 @@ config RISCV select HAVE_FTRACE_MCOUNT_RECORD if !XIP_KERNEL select HAVE_FUNCTION_GRAPH_TRACER select HAVE_FUNCTION_GRAPH_RETVAL if HAVE_FUNCTION_GRAPH_TRACER - select HAVE_FUNCTION_TRACER if !XIP_KERNEL && !PREEMPTION + select HAVE_FUNCTION_TRACER if !XIP_KERNEL select HAVE_EBPF_JIT if MMU select HAVE_GUP_FAST if MMU select HAVE_FUNCTION_ARG_ACCESS_API