arm64: Add cpucap_is_possible()

Many cpucaps can only be set when certain CONFIG_* options are selected,
and we need to check the CONFIG_* option before the cap in order to
avoid generating redundant code. Due to this, we have a growing number
of helpers in <asm/cpufeature.h> of the form:

| static __always_inline bool system_supports_foo(void)
| {
|         return IS_ENABLED(CONFIG_ARM64_FOO) &&
|                 cpus_have_const_cap(ARM64_HAS_FOO);
| }

This is unfortunate as it forces us to use cpus_have_const_cap()
unnecessarily, resulting in redundant code being generated by the
compiler. In the vast majority of cases, we only require that feature
checks indicate the presence of a feature after cpucaps have been
finalized, and so it would be sufficient to use alternative_has_cap_*().
However some code needs to handle a feature before alternatives have
been patched, and must test the system_cpucaps bitmap via
cpus_have_const_cap(). In other cases we'd like to check for
unintentional usage of a cpucap before alternatives are patched, and so
it would be preferable to use cpus_have_final_cap().

Placing the IS_ENABLED() checks in each callsite is tedious and
error-prone, and the same applies for writing wrappers for each
comination of cpucap and alternative_has_cap_*() / cpus_have_cap() /
cpus_have_final_cap(). It would be nicer if we could centralize the
knowledge of which cpucaps are possible, and have
alternative_has_cap_*(), cpus_have_cap(), and cpus_have_final_cap()
handle this automatically.

This patch adds a new cpucap_is_possible() function which will be
responsible for checking the CONFIG_* option, and updates the low-level
cpucap checks to use this. The existing CONFIG_* checks in
<asm/cpufeature.h> are moved over to cpucap_is_possible(), but the (now
trival) wrapper functions are retained for now.

There should be no functional change as a result of this patch alone.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Mark Brown <broonie@kernel.org>
Cc: 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/alternative-macros.h

@@ -226,8 +226,8 @@ alternative_endif
 static __always_inline bool
 alternative_has_cap_likely(const unsigned long cpucap)
 {
-	compiletime_assert(cpucap < ARM64_NCAPS,
-			   "cpucap must be < ARM64_NCAPS");
+	if (!cpucap_is_possible(cpucap))
+		return false;
 
 	asm_volatile_goto(
 	ALTERNATIVE_CB("b	%l[l_no]", %[cpucap], alt_cb_patch_nops)
@@ -244,8 +244,8 @@ alternative_has_cap_likely(const unsigned long cpucap)
 static __always_inline bool
 alternative_has_cap_unlikely(const unsigned long cpucap)
 {
-	compiletime_assert(cpucap < ARM64_NCAPS,
-			   "cpucap must be < ARM64_NCAPS");
+	if (!cpucap_is_possible(cpucap))
+		return false;
 
 	asm_volatile_goto(
 	ALTERNATIVE("nop", "b	%l[l_yes]", %[cpucap])

arch/arm64/include/asm/cpucaps.h

@@ -5,4 +5,45 @@
 
 #include <asm/cpucap-defs.h>
 
+#ifndef __ASSEMBLY__
+#include <linux/types.h>
+/*
+ * Check whether a cpucap is possible at compiletime.
+ */
+static __always_inline bool
+cpucap_is_possible(const unsigned int cap)
+{
+	compiletime_assert(__builtin_constant_p(cap),
+			   "cap must be a constant");
+	compiletime_assert(cap < ARM64_NCAPS,
+			   "cap must be < ARM64_NCAPS");
+
+	switch (cap) {
+	case ARM64_HAS_PAN:
+		return IS_ENABLED(CONFIG_ARM64_PAN);
+	case ARM64_SVE:
+		return IS_ENABLED(CONFIG_ARM64_SVE);
+	case ARM64_SME:
+	case ARM64_SME2:
+	case ARM64_SME_FA64:
+		return IS_ENABLED(CONFIG_ARM64_SME);
+	case ARM64_HAS_CNP:
+		return IS_ENABLED(CONFIG_ARM64_CNP);
+	case ARM64_HAS_ADDRESS_AUTH:
+	case ARM64_HAS_GENERIC_AUTH:
+		return IS_ENABLED(CONFIG_ARM64_PTR_AUTH);
+	case ARM64_HAS_GIC_PRIO_MASKING:
+		return IS_ENABLED(CONFIG_ARM64_PSEUDO_NMI);
+	case ARM64_MTE:
+		return IS_ENABLED(CONFIG_ARM64_MTE);
+	case ARM64_BTI:
+		return IS_ENABLED(CONFIG_ARM64_BTI);
+	case ARM64_HAS_TLB_RANGE:
+		return IS_ENABLED(CONFIG_ARM64_TLB_RANGE);
+	}
+
+	return true;
+}
+#endif /* __ASSEMBLY__ */
+
 #endif /* __ASM_CPUCAPS_H */

arch/arm64/include/asm/cpufeature.h

@@ -450,6 +450,8 @@ static __always_inline bool system_capabilities_finalized(void)
  */
 static __always_inline bool cpus_have_cap(unsigned int num)
 {
+	if (__builtin_constant_p(num) && !cpucap_is_possible(num))
+		return false;
 	if (num >= ARM64_NCAPS)
 		return false;
 	return arch_test_bit(num, system_cpucaps);
@@ -465,8 +467,6 @@ static __always_inline bool cpus_have_cap(unsigned int num)
  */
 static __always_inline bool __cpus_have_const_cap(int num)
 {
-	if (num >= ARM64_NCAPS)
-		return false;
 	return alternative_has_cap_unlikely(num);
 }
 
@@ -740,8 +740,7 @@ static __always_inline bool system_supports_fpsimd(void)
 
 static inline bool system_uses_hw_pan(void)
 {
-	return IS_ENABLED(CONFIG_ARM64_PAN) &&
-		cpus_have_const_cap(ARM64_HAS_PAN);
+	return cpus_have_const_cap(ARM64_HAS_PAN);
 }
 
 static inline bool system_uses_ttbr0_pan(void)
@@ -752,26 +751,22 @@ static inline bool system_uses_ttbr0_pan(void)
 
 static __always_inline bool system_supports_sve(void)
 {
-	return IS_ENABLED(CONFIG_ARM64_SVE) &&
-		cpus_have_const_cap(ARM64_SVE);
+	return cpus_have_const_cap(ARM64_SVE);
 }
 
 static __always_inline bool system_supports_sme(void)
 {
-	return IS_ENABLED(CONFIG_ARM64_SME) &&
-		cpus_have_const_cap(ARM64_SME);
+	return cpus_have_const_cap(ARM64_SME);
 }
 
 static __always_inline bool system_supports_sme2(void)
 {
-	return IS_ENABLED(CONFIG_ARM64_SME) &&
-		cpus_have_const_cap(ARM64_SME2);
+	return cpus_have_const_cap(ARM64_SME2);
 }
 
 static __always_inline bool system_supports_fa64(void)
 {
-	return IS_ENABLED(CONFIG_ARM64_SME) &&
-		cpus_have_const_cap(ARM64_SME_FA64);
+	return cpus_have_const_cap(ARM64_SME_FA64);
 }
 
 static __always_inline bool system_supports_tpidr2(void)
@@ -781,20 +776,17 @@ static __always_inline bool system_supports_tpidr2(void)
 
 static __always_inline bool system_supports_cnp(void)
 {
-	return IS_ENABLED(CONFIG_ARM64_CNP) &&
-		cpus_have_const_cap(ARM64_HAS_CNP);
+	return cpus_have_const_cap(ARM64_HAS_CNP);
 }
 
 static inline bool system_supports_address_auth(void)
 {
-	return IS_ENABLED(CONFIG_ARM64_PTR_AUTH) &&
-		cpus_have_const_cap(ARM64_HAS_ADDRESS_AUTH);
+	return cpus_have_const_cap(ARM64_HAS_ADDRESS_AUTH);
 }
 
 static inline bool system_supports_generic_auth(void)
 {
-	return IS_ENABLED(CONFIG_ARM64_PTR_AUTH) &&
-		cpus_have_const_cap(ARM64_HAS_GENERIC_AUTH);
+	return cpus_have_const_cap(ARM64_HAS_GENERIC_AUTH);
 }
 
 static inline bool system_has_full_ptr_auth(void)
@@ -804,14 +796,12 @@ static inline bool system_has_full_ptr_auth(void)
 
 static __always_inline bool system_uses_irq_prio_masking(void)
 {
-	return IS_ENABLED(CONFIG_ARM64_PSEUDO_NMI) &&
-	       cpus_have_const_cap(ARM64_HAS_GIC_PRIO_MASKING);
+	return cpus_have_const_cap(ARM64_HAS_GIC_PRIO_MASKING);
 }
 
 static inline bool system_supports_mte(void)
 {
-	return IS_ENABLED(CONFIG_ARM64_MTE) &&
-		cpus_have_const_cap(ARM64_MTE);
+	return cpus_have_const_cap(ARM64_MTE);
 }
 
 static inline bool system_has_prio_mask_debugging(void)
@@ -822,13 +812,12 @@ static inline bool system_has_prio_mask_debugging(void)
 
 static inline bool system_supports_bti(void)
 {
-	return IS_ENABLED(CONFIG_ARM64_BTI) && cpus_have_const_cap(ARM64_BTI);
+	return cpus_have_const_cap(ARM64_BTI);
 }
 
 static inline bool system_supports_tlb_range(void)
 {
-	return IS_ENABLED(CONFIG_ARM64_TLB_RANGE) &&
-		cpus_have_const_cap(ARM64_HAS_TLB_RANGE);
+	return cpus_have_const_cap(ARM64_HAS_TLB_RANGE);
 }
 
 int do_emulate_mrs(struct pt_regs *regs, u32 sys_reg, u32 rt);