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>

1 files changed, 41 insertions, 0 deletions

diff --git a/arch/arm64/include/asm/cpucaps.h b/arch/arm64/include/asm/cpucaps.h
index 7333b5bbf448..764ad4eef859 100644
--- a/arch/arm64/include/asm/cpucaps.h
+++ b/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 */