arm64: cpufeature: upgrade hyp caps to final

We finalize caps before initializing kvm hyp code, and any use of
cpus_have_const_cap() in kvm hyp code generates redundant and
potentially unsound code to read the cpu_hwcaps array.

A number of helper functions used in both hyp context and regular kernel
context use cpus_have_const_cap(), as some regular kernel code runs
before the capabilities are finalized. It's tedious and error-prone to
write separate copies of these for hyp and non-hyp code.

So that we can avoid the redundant code, let's automatically upgrade
cpus_have_const_cap() to cpus_have_final_cap() when used in hyp context.
With this change, there's never a reason to access to cpu_hwcaps array
from hyp code, and we don't need to create an NVHE alias for this.

This should have no effect on non-hyp code.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Acked-by: Will Deacon <will@kernel.org>
Cc: David Brazdil <dbrazdil@google.com>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Will Deacon <will@kernel.org>
Link: https://lore.kernel.org/r/20201026134931.28246-4-mark.rutland@arm.com

1 files changed, 24 insertions, 2 deletions

diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
index 9f671aa0419b..79d6a0371c78 100644
--- a/arch/arm64/include/asm/cpufeature.h
+++ b/arch/arm64/include/asm/cpufeature.h
@@ -375,6 +375,23 @@ cpucap_multi_entry_cap_matches(const struct arm64_cpu_capabilities *entry,
 	return false;
 }
 
+static __always_inline bool is_vhe_hyp_code(void)
+{
+	/* Only defined for code run in VHE hyp context */
+	return __is_defined(__KVM_VHE_HYPERVISOR__);
+}
+
+static __always_inline bool is_nvhe_hyp_code(void)
+{
+	/* Only defined for code run in NVHE hyp context */
+	return __is_defined(__KVM_NVHE_HYPERVISOR__);
+}
+
+static __always_inline bool is_hyp_code(void)
+{
+	return is_vhe_hyp_code() || is_nvhe_hyp_code();
+}
+
 extern DECLARE_BITMAP(cpu_hwcaps, ARM64_NCAPS);
 extern struct static_key_false cpu_hwcap_keys[ARM64_NCAPS];
 extern struct static_key_false arm64_const_caps_ready;
@@ -444,8 +461,11 @@ static __always_inline bool cpus_have_final_cap(int num)
 }
 
 /*
- * Test for a capability, possibly with a runtime check.
+ * Test for a capability, possibly with a runtime check for non-hyp code.
  *
+ * For hyp code, this behaves the same as cpus_have_final_cap().
+ *
+ * For non-hyp code:
  * Before capabilities are finalized, this behaves as cpus_have_cap().
  * After capabilities are finalized, this is patched to avoid a runtime check.
  *
@@ -453,7 +473,9 @@ static __always_inline bool cpus_have_final_cap(int num)
  */
 static __always_inline bool cpus_have_const_cap(int num)
 {
-	if (system_capabilities_finalized())
+	if (is_hyp_code())
+		return cpus_have_final_cap(num);
+	else if (system_capabilities_finalized())
 		return __cpus_have_const_cap(num);
 	else
 		return cpus_have_cap(num);