linux-kernel - [PATCH v2 18/21] arm64: KVM: Introduce hyp_alternate

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Date:	Mon, 25 Jan 2016 15:53:52 +0000
From:	Marc Zyngier <marc.zyngier@....com>
To:	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	Christoffer Dall <christoffer.dall@...aro.org>
Cc:	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org, kvmarm@...ts.cs.columbia.edu
Subject: [PATCH v2 18/21] arm64: KVM: Introduce hyp_alternate_value helper

We already have hyp_alternate_select() to define a function pointer
that gets changed by a kernel feature or workaround.

It would be useful to have a similar feature that resolves in a
direct value, without requiring a function call. For this purpose,
introduce hyp_alternate_value(), which returns one of two values
depending on the state of the alternative.

Signed-off-by: Marc Zyngier <marc.zyngier@....com>
---
 arch/arm64/kvm/hyp/hyp.h | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/arch/arm64/kvm/hyp/hyp.h b/arch/arm64/kvm/hyp/hyp.h
index 44eaff7..dc75fdb 100644
--- a/arch/arm64/kvm/hyp/hyp.h
+++ b/arch/arm64/kvm/hyp/hyp.h
@@ -144,6 +144,17 @@ typeof(orig) * __hyp_text fname(void)					\
 	return val;							\
 }
 
+#define hyp_alternate_value(fname, orig, alt, cond)			\
+typeof(orig) __hyp_text fname(void)					\
+{									\
+	typeof(alt) val = orig;						\
+	asm volatile(ALTERNATIVE("nop		\n",			\
+				 "mov	%0, %1	\n",			\
+				 cond)					\
+		     : "+r" (val) : "r" ((typeof(orig))alt));		\
+	return val;							\
+}
+
 void __vgic_v2_save_state(struct kvm_vcpu *vcpu);
 void __vgic_v2_restore_state(struct kvm_vcpu *vcpu);
 
-- 
2.1.4