@@ -776,22 +776,22 @@ static inline bool system_uses_ttbr0_pan(void)
static __always_inline bool system_supports_sve(void)
{
- return cpus_have_const_cap(ARM64_SVE);
+ return alternative_has_cap_unlikely(ARM64_SVE);
}
static __always_inline bool system_supports_sme(void)
{
- return cpus_have_const_cap(ARM64_SME);
+ return alternative_has_cap_unlikely(ARM64_SME);
}
static __always_inline bool system_supports_sme2(void)
{
- return cpus_have_const_cap(ARM64_SME2);
+ return alternative_has_cap_unlikely(ARM64_SME2);
}
static __always_inline bool system_supports_fa64(void)
{
- return cpus_have_const_cap(ARM64_SME_FA64);
+ return alternative_has_cap_unlikely(ARM64_SME_FA64);
}
static __always_inline bool system_supports_tpidr2(void)
@@ -1199,7 +1199,7 @@ void __init sve_setup(void)
DECLARE_BITMAP(tmp_map, SVE_VQ_MAX);
unsigned long b;
- if (!system_supports_sve())
+ if (!cpus_have_cap(ARM64_SVE))
return;
/*
@@ -1358,7 +1358,7 @@ void __init sme_setup(void)
u64 smcr;
int min_bit;
- if (!system_supports_sme())
+ if (!cpus_have_cap(ARM64_SME))
return;
/*
In system_supports_{sve,sme,sme2,fa64}() we use cpus_have_const_cap() to check for the relevant cpucaps, but this is only necessary so that sve_setup() and sme_setup() can run prior to alternatives being patched, and otherwise alternative_has_cap_*() would be preferable. For historical reasons, cpus_have_const_cap() is more complicated than it needs to be. Before cpucaps are finalized, it will perform a bitmap test of the system_cpucaps bitmap, and once cpucaps are finalized it will use an alternative branch. This used to be necessary to handle some race conditions in the window between cpucap detection and the subsequent patching of alternatives and static branches, where different branches could be out-of-sync with one another (or w.r.t. alternative sequences). Now that we use alternative branches instead of static branches, these are all patched atomically w.r.t. one another, and there are only a handful of cases that need special care in the window between cpucap detection and alternative patching. Due to the above, it would be nice to remove cpus_have_const_cap(), and migrate callers over to alternative_has_cap_*(), cpus_have_final_cap(), or cpus_have_cap() depending on when their requirements. This will remove redundant instructions and improve code generation, and will make it easier to determine how each callsite will behave before, during, and after alternative patching. All of system_supports_{sve,sme,sme2,fa64}() will return false prior to system cpucaps being detected. In the window between system cpucaps being detected and patching alternatives, we need system_supports_sve() and system_supports_sme() to run to initialize SVE and SME properties, but all other users of system_supports_{sve,sme,sme2,fa64}() don't depend on the relevant cpucap becoming true until alternatives are patched: * No KVM code runs until after alternatives are patched, and so this can safely use cpus_have_final_cap() or alternative_has_cap_*(). * The cpuid_cpu_online() callback in arch/arm64/kernel/cpuinfo.c is registered later from cpuinfo_regs_init() as a device_initcall, and so this can safely use cpus_have_final_cap() or alternative_has_cap_*(). * The entry, signal, and ptrace code isn't reachable until userspace has run, and so this can safely use cpus_have_final_cap() or alternative_has_cap_*(). * Currently perf_reg_validate() will un-reserve the PERF_REG_ARM64_VG pseudo-register before alternatives are patched, and before sve_setup() has run. If a sampling event is created early enough, this would allow perf_ext_reg_value() to sample (the as-yet uninitialized) thread_struct::vl[] prior to alternatives being patched. It would be preferable to defer this until alternatives are patched, and this can safely use alternative_has_cap_*(). * The context-switch code will run during this window as part of stop_machine() used during alternatives_patch_all(), and potentially for other work if other kernel threads are created early. No threads require the use of SVE/SME/SME2/FA64 prior to alternatives being patched, and it would be preferable for the related context-switch logic to take effect after alternatives are patched so that ths is guaranteed to see a consistent system-wide state (e.g. anything initialized by sve_setup() and sme_setup(). This can safely ues alternative_has_cap_*(). This patch replaces the use of cpus_have_const_cap() with alternative_has_cap_unlikely(), which will avoid generating code to test the system_cpucaps bitmap and should be better for all subsequent calls at runtime. The sve_setup() and sme_setup() functions are modified to use cpus_have_cap() directly so that they can observe the cpucaps being set prior to alternatives being patched. Signed-off-by: Mark Rutland <mark.rutland@arm.com> Reviewed-by: Mark Brown <broonie@kernel.org> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Suzuki K Poulose <suzuki.poulose@arm.com> Cc: Will Deacon <will@kernel.org> --- arch/arm64/include/asm/cpufeature.h | 8 ++++---- arch/arm64/kernel/fpsimd.c | 4 ++-- 2 files changed, 6 insertions(+), 6 deletions(-)