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arm64/sme: Optimise SME exit on syscall entry
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> Link: https://lore.kernel.org/r/20230110-arm64-sme-syscall-smstop-v1-1-ac94235fd810@kernel.org Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
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1 changed files with 2 additions and 6 deletions
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@ -173,12 +173,8 @@ static inline void fp_user_discard(void)
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* register state to track, if this changes the KVM code will
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* need updating.
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*/
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if (system_supports_sme() && test_thread_flag(TIF_SME)) {
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u64 svcr = read_sysreg_s(SYS_SVCR);
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if (svcr & SVCR_SM_MASK)
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sme_smstop_sm();
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}
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if (system_supports_sme())
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sme_smstop_sm();
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if (!system_supports_sve())
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return;
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