Revision 5d5fc33ce58e81e8738816f5ee59f8e85fd3b404 authored by Anton Blanchard on 07 June 2024, 06:13:35 UTC, committed by Palmer Dabbelt on 26 July 2024, 12:50:45 UTC
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>
1 parent 8d22d0d
Kbuild
# SPDX-License-Identifier: GPL-2.0
#
# Kbuild for top-level directory of the kernel
# Prepare global headers and check sanity before descending into sub-directories
# ---------------------------------------------------------------------------
# Generate bounds.h
bounds-file := include/generated/bounds.h
targets := kernel/bounds.s
$(bounds-file): kernel/bounds.s FORCE
$(call filechk,offsets,__LINUX_BOUNDS_H__)
# Generate timeconst.h
timeconst-file := include/generated/timeconst.h
filechk_gentimeconst = echo $(CONFIG_HZ) | bc -q $<
$(timeconst-file): kernel/time/timeconst.bc FORCE
$(call filechk,gentimeconst)
# Generate asm-offsets.h
offsets-file := include/generated/asm-offsets.h
targets += arch/$(SRCARCH)/kernel/asm-offsets.s
arch/$(SRCARCH)/kernel/asm-offsets.s: $(timeconst-file) $(bounds-file)
$(offsets-file): arch/$(SRCARCH)/kernel/asm-offsets.s FORCE
$(call filechk,offsets,__ASM_OFFSETS_H__)
# Check for missing system calls
quiet_cmd_syscalls = CALL $<
cmd_syscalls = $(CONFIG_SHELL) $< $(CC) $(c_flags) $(missing_syscalls_flags)
PHONY += missing-syscalls
missing-syscalls: scripts/checksyscalls.sh $(offsets-file)
$(call cmd,syscalls)
# Check the manual modification of atomic headers
quiet_cmd_check_sha1 = CHKSHA1 $<
cmd_check_sha1 = \
if ! command -v sha1sum >/dev/null; then \
echo "warning: cannot check the header due to sha1sum missing"; \
exit 0; \
fi; \
if [ "$$(sed -n '$$s:// ::p' $<)" != \
"$$(sed '$$d' $< | sha1sum | sed 's/ .*//')" ]; then \
echo "error: $< has been modified." >&2; \
exit 1; \
fi; \
touch $@
atomic-checks += $(addprefix $(obj)/.checked-, \
atomic-arch-fallback.h \
atomic-instrumented.h \
atomic-long.h)
targets += $(atomic-checks)
$(atomic-checks): $(obj)/.checked-%: include/linux/atomic/% FORCE
$(call if_changed,check_sha1)
# A phony target that depends on all the preparation targets
PHONY += prepare
prepare: $(offsets-file) missing-syscalls $(atomic-checks)
@:
# Ordinary directory descending
# ---------------------------------------------------------------------------
obj-y += init/
obj-y += usr/
obj-y += arch/$(SRCARCH)/
obj-y += $(ARCH_CORE)
obj-y += kernel/
obj-y += certs/
obj-y += mm/
obj-y += fs/
obj-y += ipc/
obj-y += security/
obj-y += crypto/
obj-$(CONFIG_BLOCK) += block/
obj-$(CONFIG_IO_URING) += io_uring/
obj-$(CONFIG_RUST) += rust/
obj-y += $(ARCH_LIB)
obj-y += drivers/
obj-y += sound/
obj-$(CONFIG_SAMPLES) += samples/
obj-$(CONFIG_NET) += net/
obj-y += virt/
obj-y += $(ARCH_DRIVERS)
Computing file changes ...
