arm64: cpufeature: add cpus_have_final_cap() (1db5cdec) · Commits · 戴 / test

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: ("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: ("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 <mark.rutland@arm.com> Reviewed-by:

Marc Zyngier <maz@kernel.org> Reviewed-by:

Suzuki K Poulose <suzuki.poulose@arm.com> Cc: Will Deacon <will@kernel.org> Signed-off-by:

Catalin Marinas <catalin.marinas@arm.com>

arch/arm64/include/asm/cpufeature.h

+47 −11

Original line number	Diff line number	Diff line
		@@ -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

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