3 Commits

Author	SHA1	Message	Date
Andy Chiu	9ddfc3cd80	riscv: jump_label: Fixup unaligned arch_static_branch function ... Runtime code patching must be done at a naturally aligned address, or we may execute on a partial instruction. We have encountered problems traced back to static jump functions during the test. We switched the tracer randomly for every 1~5 seconds on a dual-core QEMU setup and found the kernel sucking at a static branch where it jumps to itself. The reason is that the static branch was 2-byte but not 4-byte aligned. Then, the kernel would patch the instruction, either J or NOP, with two half-word stores if the machine does not have efficient unaligned accesses. Thus, moments exist where half of the NOP mixes with the other half of the J when transitioning the branch. In our particular case, on a little-endian machine, the upper half of the NOP was mixed with the lower part of the J when enabling the branch, resulting in a jump that jumped to itself. Conversely, it would result in a HINT instruction when disabling the branch, but it might not be observable. ARM64 does not have this problem since all instructions must be 4-byte aligned. Fixes: ebc00dde8a97 ("riscv: Add jump-label implementation") Link: https://lore.kernel.org/linux-riscv/20220913094252.3555240-6-andy.chiu@sifive.com/ Reviewed-by: Greentime Hu <greentime.hu@sifive.com> Signed-off-by: Andy Chiu <andy.chiu@sifive.com> Signed-off-by: Guo Ren <guoren@kernel.org> Link: https://lore.kernel.org/r/20230206090440.1255001-1-guoren@kernel.org Cc: stable@vger.kernel.org Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>	2023-02-21 17:21:16 -08:00
Jisheng Zhang	89fd4a1df8	riscv: jump_label: mark arguments as const to satisfy asm constraints ... Samuel reported that the static branch usage in cpu_relax() breaks building with CONFIG_CC_OPTIMIZE_FOR_SIZE: In file included from <command-line>: ./arch/riscv/include/asm/jump_label.h: In function 'cpu_relax': ././include/linux/compiler_types.h:285:33: warning: 'asm' operand 0 probably does not match constraints 285 | #define asm_volatile_goto(x...) asm goto(x) | ^~~ ./arch/riscv/include/asm/jump_label.h:41:9: note: in expansion of macro 'asm_volatile_goto' 41 | asm_volatile_goto( | ^~~~~~~~~~~~~~~~~ ././include/linux/compiler_types.h:285:33: error: impossible constraint in 'asm' 285 | #define asm_volatile_goto(x...) asm goto(x) | ^~~ ./arch/riscv/include/asm/jump_label.h:41:9: note: in expansion of macro 'asm_volatile_goto' 41 | asm_volatile_goto( | ^~~~~~~~~~~~~~~~~ make[1]: *** [scripts/Makefile.build:249: arch/riscv/kernel/vdso/vgettimeofday.o] Error 1 make: *** [arch/riscv/Makefile:128: vdso_prepare] Error 2 Maybe "-Os" prevents GCC from detecting that the key/branch arguments can be treated as constants and used as immediate operands. Inspired by x86's commit 864b435514b2("x86/jump_label: Mark arguments as const to satisfy asm constraints"), and as pointed out by Steven: "The "i" constraint needs to be a constant.", let's do similar modifications to riscv. Tested by CC_OPTIMIZE_FOR_SIZE + gcc and CC_OPTIMIZE_FOR_SIZE + clang. Link: https://lore.kernel.org/linux-riscv/20220922060958.44203-1-samuel@sholland.org/ Link: https://lore.kernel.org/all/20210212094059.5f8d05e8@gandalf.local.home/ Fixes: 8eb060e10185 ("arch/riscv: add Zihintpause support") Reported-by: Samuel Holland <samuel@sholland.org> Signed-off-by: Jisheng Zhang <jszhang@kernel.org> Reviewed-by: Andrew Jones <ajones@ventanamicro.com> Tested-by: Heiko Stuebner <heiko@sntech.de> Link: https://lore.kernel.org/r/20221008145437.491-1-jszhang@kernel.org Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>	2022-10-25 23:09:45 -07:00
Emil Renner Berthing	ebc00dde8a	riscv: Add jump-label implementation ... Add jump-label implementation based on the ARM64 version and add CONFIG_JUMP_LABEL=y to the defconfigs. Signed-off-by: Emil Renner Berthing <kernel@esmil.dk> Reviewed-by: Björn Töpel <bjorn.topel@gmail.com> Tested-by: Björn Töpel <bjorn.topel@gmail.com> Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>	2020-07-30 11:37:43 -07:00