For the rationale to implement getrandom() in vDSO see [1].
The vDSO getrandom() needs a stack-less ChaCha20 implementation, so we
need to add architecture-specific code and wire it up with the generic
code.
Without LSX it's not easy to implement ChaCha20 without stack. So the
current implementation just falls back to a getrandom() syscall if LSX
is unavailable. In the 1st patch the existing alternative runtime
patching mechanism is expanded to cover vDSO in the first patch, so we
don't need to invoke cpucfg for each vDSO getrandom() call.
Then in the 2nd patch stack-less ChaCha20 is implemented with LSX. The
code is basically a direct translate from the x86 SSE2 implementation.
One annoying thing here is the compiler generates a memset() call for a
"large" struct initialization in a cold path and there seems no way to
prevent it. So a naive memset implementation is copied from the kernel
code into vDSO.
The implementation is tested with the kernel selftests added by the last
patch in [1]. I had to make some adjustments to make it work on
LoongArch (see [2], I've not submitted the changes as at now because I'm
unsure about the KHDR_INCLUDES addition). The vdso_test_getrandom
bench-single result:
vdso: 25000000 times in 0.631345201 seconds
libc: 25000000 times in 6.953121083 seconds
syscall: 25000000 times in 6.992112386 seconds
The vdso_test_getrandom bench-multi result:
vdso: 25000000 x 256 times in 29.558284986 seconds
libc: 25000000 x 256 times in 356.633930139 seconds
syscall: 25000000 x 256 times in 334.885555338 seconds
[1]:https://lore.kernel.org/all/20240712014009.281406-1-Jason@xxxxxxxxx/
[2]:https://github.com/xry111/linux/commits/xry111/la-vdso/
v1->v2: Remove Cc: lists in the cover letter and just type them in git
send-email command. I assumed the Cc: lists in the cover letter would be
"propagated" to the patches by git send-email but I was wrong, so v1 was
never properly delivered to the lists.
Xi Ruoyao (2):
LoongArch: Perform alternative runtime patching on vDSO
LoongArch: vDSO: Wire up getrandom() vDSO implementation
arch/loongarch/Kconfig | 1 +
arch/loongarch/include/asm/vdso/getrandom.h | 47 ++++++
arch/loongarch/include/asm/vdso/vdso.h | 8 +
arch/loongarch/kernel/asm-offsets.c | 10 ++
arch/loongarch/kernel/vdso.c | 14 +-
arch/loongarch/vdso/Makefile | 2 +
arch/loongarch/vdso/memset.S | 24 +++
arch/loongarch/vdso/vdso.lds.S | 7 +
arch/loongarch/vdso/vgetrandom-alt.S | 19 +++
arch/loongarch/vdso/vgetrandom-chacha.S | 162 ++++++++++++++++++++
arch/loongarch/vdso/vgetrandom.c | 16 ++
11 files changed, 309 insertions(+), 1 deletion(-)
create mode 100644 arch/loongarch/include/asm/vdso/getrandom.h
create mode 100644 arch/loongarch/vdso/memset.S
create mode 100644 arch/loongarch/vdso/vgetrandom-alt.S
create mode 100644 arch/loongarch/vdso/vgetrandom-chacha.S
create mode 100644 arch/loongarch/vdso/vgetrandom.c
--
2.46.0
