KVM: arm64: Prevent vcpu_has_ptrauth from generating OOL functions

So far, vcpu_has_ptrauth() is implemented in terms of system_supports_*_auth()
calls, which are declared "inline". In some specific conditions (clang
and SCS), the "inline" very much turns into an "out of line", which
leads to a fireworks when this predicate is evaluated on a non-VHE
system (right at the beginning of __hyp_handle_ptrauth).

Instead, make sure vcpu_has_ptrauth gets expanded inline by directly
using the cpus_have_final_cap() helpers, which are __always_inline,
generate much better code, and are the only thing that make sense when
running at EL2 on a nVHE system.

Fixes: 29eb5a3 ("KVM: arm64: Handle PtrAuth traps early")
Reported-by: Nathan Chancellor <natechancellor@gmail.com>
Reported-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Tested-by: Nathan Chancellor <natechancellor@gmail.com>
Reviewed-by: Nathan Chancellor <natechancellor@gmail.com>
Link: https://lore.kernel.org/r/20200722162231.3689767-1-maz@kernel.org

Author: Marc Zyngier

arch/arm64/include/asm/kvm_host.h

@@ -380,9 +380,14 @@ struct kvm_vcpu_arch {
 #define vcpu_has_sve(vcpu) (system_supports_sve() && \
 			    ((vcpu)->arch.flags & KVM_ARM64_GUEST_HAS_SVE))
 
-#define vcpu_has_ptrauth(vcpu)	((system_supports_address_auth() || \
-				  system_supports_generic_auth()) && \
-				 ((vcpu)->arch.flags & KVM_ARM64_GUEST_HAS_PTRAUTH))
+#ifdef CONFIG_ARM64_PTR_AUTH
+#define vcpu_has_ptrauth(vcpu)						\
+	((cpus_have_final_cap(ARM64_HAS_ADDRESS_AUTH) ||		\
+	  cpus_have_final_cap(ARM64_HAS_GENERIC_AUTH)) &&		\
+	 (vcpu)->arch.flags & KVM_ARM64_GUEST_HAS_PTRAUTH)
+#else
+#define vcpu_has_ptrauth(vcpu)		false
+#endif
 
 #define vcpu_gp_regs(v)		(&(v)->arch.ctxt.gp_regs)