From 1db5cdeccd813330aaab19b3fccab15e1d07fe12 Mon Sep 17 00:00:00 2001 From: Mark Rutland Date: Fri, 21 Feb 2020 14:50:21 +0000 Subject: arm64: cpufeature: add cpus_have_final_cap() When cpus_have_const_cap() was originally introduced it was intended to be safe in hyp context, where it is not safe to access the cpu_hwcaps array as cpus_have_cap() did. For more details see commit: a4023f682739439b ("arm64: Add hypervisor safe helper for checking constant capabilities") We then made use of cpus_have_const_cap() throughout the kernel. Subsequently, we had to defer updating the static_key associated with each capability in order to avoid lockdep complaints. To avoid breaking kernel-wide usage of cpus_have_const_cap(), this was updated to fall back to the cpu_hwcaps array if called before the static_keys were updated. As the kvm hyp code was only called later than this, the fallback is redundant but not functionally harmful. For more details, see commit: 63a1e1c95e60e798 ("arm64/cpufeature: don't use mutex in bringup path") Today we have more users of cpus_have_const_cap() which are only called once the relevant static keys are initialized, and it would be beneficial to avoid the redundant code. To that end, this patch adds a new cpus_have_final_cap(), helper which is intend to be used in code which is only run once capabilities have been finalized, and will never check the cpus_hwcap array. This helps the compiler to generate better code as it no longer needs to generate code to address and test the cpus_hwcap array. To help catch misuse, cpus_have_final_cap() will BUG() if called before capabilities are finalized. In hyp context, BUG() will result in a hyp panic, but the specific BUG() instance will not be identified in the usual way. Comments are added to the various cpus_have_*_cap() helpers to describe the constraints on when they can be used. For clarity cpus_have_cap() is moved above the other helpers. Similarly the helpers are updated to use system_capabilities_finalized() consistently, and this is made __always_inline as required by its new callers. Signed-off-by: Mark Rutland Reviewed-by: Marc Zyngier Reviewed-by: Suzuki K Poulose Cc: Will Deacon Signed-off-by: Catalin Marinas --- arch/arm64/include/asm/cpufeature.h | 58 ++++++++++++++++++++++++++++++------- 1 file changed, 47 insertions(+), 11 deletions(-) diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h index 92ef9539874a..940b2b67b428 100644 --- a/arch/arm64/include/asm/cpufeature.h +++ b/arch/arm64/include/asm/cpufeature.h @@ -390,14 +390,16 @@ unsigned long cpu_get_elf_hwcap2(void); #define cpu_set_named_feature(name) cpu_set_feature(cpu_feature(name)) #define cpu_have_named_feature(name) cpu_have_feature(cpu_feature(name)) -/* System capability check for constant caps */ -static __always_inline bool __cpus_have_const_cap(int num) +static __always_inline bool system_capabilities_finalized(void) { - if (num >= ARM64_NCAPS) - return false; - return static_branch_unlikely(&cpu_hwcap_keys[num]); + return static_branch_likely(&arm64_const_caps_ready); } +/* + * Test for a capability with a runtime check. + * + * Before the capability is detected, this returns false. + */ static inline bool cpus_have_cap(unsigned int num) { if (num >= ARM64_NCAPS) @@ -405,14 +407,53 @@ static inline bool cpus_have_cap(unsigned int num) return test_bit(num, cpu_hwcaps); } +/* + * Test for a capability without a runtime check. + * + * Before capabilities are finalized, this returns false. + * After capabilities are finalized, this is patched to avoid a runtime check. + * + * @num must be a compile-time constant. + */ +static __always_inline bool __cpus_have_const_cap(int num) +{ + if (num >= ARM64_NCAPS) + return false; + return static_branch_unlikely(&cpu_hwcap_keys[num]); +} + +/* + * Test for a capability, possibly with a runtime check. + * + * Before capabilities are finalized, this behaves as cpus_have_cap(). + * After capabilities are finalized, this is patched to avoid a runtime check. + * + * @num must be a compile-time constant. + */ static __always_inline bool cpus_have_const_cap(int num) { - if (static_branch_likely(&arm64_const_caps_ready)) + if (system_capabilities_finalized()) return __cpus_have_const_cap(num); else return cpus_have_cap(num); } +/* + * Test for a capability without a runtime check. + * + * Before capabilities are finalized, this will BUG(). + * After capabilities are finalized, this is patched to avoid a runtime check. + * + * @num must be a compile-time constant. + */ +static __always_inline bool cpus_have_final_cap(int num) +{ + if (system_capabilities_finalized()) + return __cpus_have_const_cap(num); + else + BUG(); +} + static inline void cpus_set_cap(unsigned int num) { if (num >= ARM64_NCAPS) { @@ -613,11 +654,6 @@ static inline bool system_has_prio_mask_debugging(void) system_uses_irq_prio_masking(); } -static inline bool system_capabilities_finalized(void) -{ - return static_branch_likely(&arm64_const_caps_ready); -} - #define ARM64_BP_HARDEN_UNKNOWN -1 #define ARM64_BP_HARDEN_WA_NEEDED 0 #define ARM64_BP_HARDEN_NOT_REQUIRED 1 -- cgit v1.2.3