Anton Blanchard 5d5fc33ce5 riscv: Improve exception and system call latency ... Many CPUs implement return address branch prediction as a stack. The RISCV architecture refers to this as a return address stack (RAS). If this gets corrupted then the CPU will mispredict at least one but potentally many function returns. There are two issues with the current RISCV exception code: - We are using the alternate link stack (x5/t0) for the indirect branch which makes the hardware think this is a function return. This will corrupt the RAS. - We modify the return address of handle_exception to point to ret_from_exception. This will also corrupt the RAS. Testing the null system call latency before and after the patch: Visionfive2 (StarFive JH7110 / U74) baseline: 189.87 ns patched: 176.76 ns Lichee pi 4a (T-Head TH1520 / C910) baseline: 666.58 ns patched: 636.90 ns Just over 7% on the U74 and just over 4% on the C910. Signed-off-by: Anton Blanchard <antonb@tenstorrent.com> Signed-off-by: Cyril Bur <cyrilbur@tenstorrent.com> Tested-by: Jisheng Zhang <jszhang@kernel.org> Reviewed-by: Jisheng Zhang <jszhang@kernel.org> Link: https://lore.kernel.org/r/20240607061335.2197383-1-cyrilbur@tenstorrent.com Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>		2024-07-26 05:50:45 -07:00
..
compat_vdso	Makefile: remove redundant tool coverage variables	2024-05-14 23:35:48 +09:00
pi	Makefile: remove redundant tool coverage variables	2024-05-14 23:35:48 +09:00
probes	trace: riscv: Remove deprecated kprobe on ftrace support	2024-07-24 06:14:05 -07:00
tests	treewide: replace or remove redundant def_bool in Kconfig files	2024-02-20 20:47:45 +09:00
vdso	Makefile: remove redundant tool coverage variables	2024-05-14 23:35:48 +09:00
vendor_extensions	riscv: Extend cpufeature.c to detect vendor extensions	2024-07-22 15:36:54 -07:00
.gitignore	.gitignore: add SPDX License Identifier	2020-03-25 11:50:48 +01:00
acpi_numa.c	ACPI: RISCV: Add NUMA support based on SRAT and SLIT	2024-07-22 07:13:06 -07:00
acpi.c	ACPI: RISCV: Add NUMA support based on SRAT and SLIT	2024-07-22 07:13:06 -07:00
alternative.c	riscv: errata: Rename defines for Andes	2024-03-12 07:13:12 -07:00
asm-offsets.c	ftrace: riscv: move from REGS to ARGS	2024-05-22 16:12:48 -07:00
cacheinfo.c	RISC-V Patches for the 6.4 Merge Window, Part 1	2023-04-28 16:55:39 -07:00
cfi.c	bpf, riscv64/cfi: Support kCFI + BPF on riscv64	2024-03-06 15:18:16 -08:00
compat_signal.c	riscv: compat: signal: Add rt_frame implementation	2022-05-17 16:37:21 -07:00
compat_syscall_table.c	riscv: convert to generic syscall table	2024-07-10 14:23:38 +02:00
copy-unaligned.h	RISC-V: Probe for unaligned access speed	2023-09-01 09:06:25 -07:00
copy-unaligned.S	riscv: Use SYM_*() assembly macros instead of deprecated ones	2023-11-06 09:42:47 -08:00
cpu_ops_sbi.c	riscv: prevent pt_regs corruption for secondary idle threads	2024-05-30 09:42:51 -07:00
cpu_ops_spinwait.c	riscv: prevent pt_regs corruption for secondary idle threads	2024-05-30 09:42:51 -07:00
cpu_ops.c	riscv: Use the same CPU operations for all CPUs	2024-01-04 15:03:07 -08:00
cpu-hotplug.c	riscv: Use the same CPU operations for all CPUs	2024-01-04 15:03:07 -08:00
cpu.c	riscv: Add vendor extensions to /proc/cpuinfo	2024-07-22 15:36:55 -07:00
cpufeature.c	riscv: Extend cpufeature.c to detect vendor extensions	2024-07-22 15:36:54 -07:00
crash_dump.c	vmcore: convert copy_oldmem_page() to take an iov_iter	2022-04-29 14:37:59 -07:00
crash_save_regs.S	RISC-V: Fixup get incorrect user mode PC for kernel mode regs	2022-08-11 08:54:40 -07:00
efi-header.S	riscv: Prepare EFI header for relocatable kernels	2023-04-19 07:46:28 -07:00
efi.c	riscv: Use accessors to page table entries instead of direct dereference	2023-12-20 10:48:15 -08:00
elf_kexec.c	fix missing vmalloc.h includes	2024-04-25 20:55:49 -07:00
entry.S	riscv: Improve exception and system call latency	2024-07-26 05:50:45 -07:00
fpu.S	riscv: typo in comment for get_f64_reg	2024-05-22 16:12:53 -07:00
ftrace.c	riscv: patch: Flush the icache right after patching to avoid illegal insns	2024-06-26 07:37:27 -07:00
head.h	riscv: entry: Convert to generic entry	2023-03-23 08:47:00 -07:00
head.S	riscv: set trap vector earlier	2024-07-12 08:55:31 -07:00
hibernate-asm.S	riscv: Use SYM_*() assembly macros instead of deprecated ones	2023-11-06 09:42:47 -08:00
hibernate.c	riscv: hibernate: remove WARN_ON in save_processor_state	2023-06-23 10:06:22 -07:00
image-vars.h	efi: move screen_info into efi init code	2023-10-17 16:33:39 +02:00
irq.c	Merge patch "drivers: perf: Do not broadcast to other cpus when starting a counter"	2023-11-09 06:44:13 -08:00
jump_label.c	riscv: jump_label: Batch icache maintenance	2024-06-26 07:36:27 -07:00
kernel_mode_fpu.c	riscv: add support for kernel-mode FPU	2024-05-19 14:36:19 -07:00
kernel_mode_vector.c	riscv: vector: allow kernel-mode Vector with preemption	2024-01-16 07:14:02 -08:00
kexec_relocate.S	riscv: kexec: Cleanup riscv_kexec_relocate	2023-09-20 02:53:29 -07:00
kgdb.c	RISC-V: rename parse_asm.h to insn.h	2022-12-29 06:59:47 -08:00
machine_kexec_file.c	RISC-V: Add kexec_file support	2022-05-19 12:14:18 -07:00
machine_kexec.c	riscv: kexec: Avoid deadlock in kexec crash path	2024-07-03 13:11:30 -07:00
Makefile	Merge patch series "riscv: Separate vendor extensions from standard extensions"	2024-07-22 15:37:01 -07:00
Makefile.syscalls	riscv: convert to generic syscall table	2024-07-10 14:23:38 +02:00
mcount-dyn.S	ftrace: riscv: move from REGS to ARGS	2024-05-22 16:12:48 -07:00
mcount.S	riscv: remove MCOUNT_NAME workaround	2024-02-22 15:38:54 -08:00
module-sections.c	riscv: add missing header file includes	2019-10-28 00:46:01 -07:00
module.c	arch: make execmem setup available regardless of CONFIG_MODULES	2024-05-14 00:31:44 -07:00
paravirt.c	RISC-V: KVM: Rename the SBI_STA_SHMEM_DISABLE to a generic name	2024-04-22 11:13:52 +05:30
patch.c	RISC-V Patches for the 6.11 Merge Window, Part 1	2024-07-20 09:11:27 -07:00
perf_callchain.c	riscv: Fix fill_callchain return value	2022-03-30 23:01:42 -07:00
perf_regs.c	perf/arch: Remove perf_sample_data::regs_user_copy	2020-11-09 18:12:34 +01:00
process.c	riscv: process: Fix kernel gp leakage	2024-04-04 12:35:05 -07:00
ptrace.c	Merge patch series "riscv: Introduce compat-mode helpers & improve arch_get_mmap_end()"	2024-03-20 08:56:05 -07:00
reset.c	riscv: Use do_kernel_power_off()	2022-05-19 19:30:30 +02:00
return_address.c	riscv: add CALLER_ADDRx support	2024-02-22 12:17:47 -08:00
riscv_ksyms.c	RISC-V: add infrastructure to allow different str* implementations	2023-01-31 11:43:23 -08:00
sbi-ipi.c	riscv: Use IPIs for remote cache/TLB flushes by default	2024-04-29 10:49:26 -07:00
sbi.c	riscv: Improve sbi_ecall() code generation by reordering arguments	2024-07-10 13:30:56 -07:00
setup.c	ACPI: RISCV: Add NUMA support based on SRAT and SLIT	2024-07-22 07:13:06 -07:00
signal.c	riscv: Fix vector state restore in rt_sigreturn()	2024-04-03 16:10:25 -07:00
smp.c	riscv: Use IPIs for remote cache/TLB flushes by default	2024-04-29 10:49:26 -07:00
smpboot.c	Merge patch series "Add ACPI NUMA support for RISC-V"	2024-07-22 10:31:51 -07:00
soc.c	riscv: Fix builtin DTB handling	2021-01-07 19:00:50 -08:00
stacktrace.c	riscv: Improve exception and system call latency	2024-07-26 05:50:45 -07:00
suspend_entry.S	riscv: Use SYM_*() assembly macros instead of deprecated ones	2023-11-06 09:42:47 -08:00
suspend.c	riscv: Do not save the scratch CSR during suspend	2024-04-28 14:50:36 -07:00
sys_hwprobe.c	RISC-V: hwprobe: sort EXT_KEY()s in hwprobe_isa_ext0() alphabetically	2024-07-22 10:57:41 -07:00
sys_riscv.c	syscalls: mmap(): use unsigned offset type consistently	2024-06-25 15:57:38 +02:00
syscall_table.c	riscv: convert to generic syscall table	2024-07-10 14:23:38 +02:00
time.c	RISC-V: paravirt: Add skeleton for pv-time support	2023-12-30 11:25:03 +05:30
traps_misaligned.c	riscv: misaligned: remove CONFIG_RISCV_M_MODE specific code	2024-04-28 14:50:37 -07:00
traps.c	riscv: use KERN_INFO in do_trap	2024-04-04 12:12:14 -07:00
unaligned_access_speed.c	riscv: Use kcalloc() instead of kzalloc()	2024-03-20 08:56:07 -07:00
vdso.c	riscv: vdso: Use generic union vdso_data_store	2024-02-20 20:56:00 +01:00
vector.c	riscv: vector: adjust minimum Vector requirement to ZVE32X	2024-05-30 14:33:10 -07:00
vendor_extensions.c	riscv: Extend cpufeature.c to detect vendor extensions	2024-07-22 15:36:54 -07:00
vmcore_info.c	crash: split vmcoreinfo exporting code out from crash_core.c	2024-02-23 17:48:22 -08:00
vmlinux-xip.lds.S	riscv: Check if the code to patch lies in the exit section	2024-01-09 10:58:59 -08:00
vmlinux.lds.S	riscv: Check if the code to patch lies in the exit section	2024-01-09 10:58:59 -08:00