| Message ID | 20230110-arm64-sme-syscall-smstop-v1-1-ac94235fd810@kernel.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | arm64/sme: Optimise SME exit on syscall entry | expand |
On Tue, 10 Jan 2023 19:34:36 +0000, Mark Brown wrote: > Our ABI says that we exit streaming mode on syscall entry. Currently we > check if we are in streaming mode before doing this but since we have a > SMSTOP SM instruction which will clear SVCR.SM in a single atomic operation > we can save ourselves the read of the system register and check of the flag > and just unconditionally do the SMSTOP SM. If we are not in streaming mode > it results in a noop change to SVCR, if we are in streaming mode we will > exit as desired. > > [...] Applied to arm64 (for-next/sme), thanks! [1/1] arm64/sme: Optimise SME exit on syscall entry https://git.kernel.org/arm64/c/b2482807fbd4
diff --git a/arch/arm64/kernel/syscall.c b/arch/arm64/kernel/syscall.c index a5de47e3df2b..da84cf855c44 100644 --- a/arch/arm64/kernel/syscall.c +++ b/arch/arm64/kernel/syscall.c @@ -173,12 +173,8 @@ static inline void fp_user_discard(void) * register state to track, if this changes the KVM code will * need updating. */ - if (system_supports_sme() && test_thread_flag(TIF_SME)) { - u64 svcr = read_sysreg_s(SYS_SVCR); - - if (svcr & SVCR_SM_MASK) - sme_smstop_sm(); - } + if (system_supports_sme()) + sme_smstop_sm(); if (!system_supports_sve()) return;
Our ABI says that we exit streaming mode on syscall entry. Currently we check if we are in streaming mode before doing this but since we have a SMSTOP SM instruction which will clear SVCR.SM in a single atomic operation we can save ourselves the read of the system register and check of the flag and just unconditionally do the SMSTOP SM. If we are not in streaming mode it results in a noop change to SVCR, if we are in streaming mode we will exit as desired. No functional change. Signed-off-by: Mark Brown <broonie@kernel.org> --- arch/arm64/kernel/syscall.c | 8 ++------ 1 file changed, 2 insertions(+), 6 deletions(-) --- base-commit: b7bfaa761d760e72a969d116517eaa12e404c262 change-id: 20230110-arm64-sme-syscall-smstop-4d12346f6b68 Best regards,