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arm64: Use a positive cpucap for FP/SIMD
Currently we have a negative cpucap which describes the *absence* of FP/SIMD rather than *presence* of FP/SIMD. This largely works, but is somewhat awkward relative to other cpucaps that describe the presence of a feature, and it would be nicer to have a cpucap which describes the presence of FP/SIMD: * This will allow the cpucap to be treated as a standard ARM64_CPUCAP_SYSTEM_FEATURE, which can be detected with the standard has_cpuid_feature() function and ARM64_CPUID_FIELDS() description. * This ensures that the cpucap will only transition from not-present to present, reducing the risk of unintentional and/or unsafe usage of FP/SIMD before cpucaps are finalized. * This will allow using arm64_cpu_capabilities::cpu_enable() to enable the use of FP/SIMD later, with FP/SIMD being disabled at boot time otherwise. This will ensure that any unintentional and/or unsafe usage of FP/SIMD prior to this is trapped, and will ensure that FP/SIMD is never unintentionally enabled for userspace in mismatched big.LITTLE systems. This patch replaces the negative ARM64_HAS_NO_FPSIMD cpucap with a positive ARM64_HAS_FPSIMD cpucap, making changes as described above. Note that as FP/SIMD will now be trapped when not supported system-wide, do_fpsimd_acc() must handle these traps in the same way as for SVE and SME. The commentary in fpsimd_restore_current_state() is updated to describe the new scheme. No users of system_supports_fpsimd() need to know that FP/SIMD is available prior to alternatives being patched, so this is updated to use alternative_has_cap_likely() to check for the ARM64_HAS_FPSIMD cpucap, without generating code to test the system_cpucaps bitmap. Signed-off-by: Mark Rutland <[email protected]> Reviewed-by: Mark Brown <[email protected]> Cc: Suzuki K Poulose <[email protected]> Cc: Will Deacon <[email protected]> Signed-off-by: Catalin Marinas <[email protected]>
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