arm64: KVM: VHE: Patch out kern_hyp_va

The kern_hyp_va macro is pretty meaninless with VHE, as there is
only one mapping - the kernel one.

In order to keep the code readable and efficient, use runtime
patching to replace the 'and' instruction used to compute the VA
with a 'nop'.

Reviewed-by: Christoffer Dall <christoffer.dall@linaro.org>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>

arch/arm64/include/asm/kvm_mmu.h

@@ -23,13 +23,16 @@
 #include <asm/cpufeature.h>
 
 /*
- * As we only have the TTBR0_EL2 register, we cannot express
+ * As ARMv8.0 only has the TTBR0_EL2 register, we cannot express
  * "negative" addresses. This makes it impossible to directly share
  * mappings with the kernel.
  *
  * Instead, give the HYP mode its own VA region at a fixed offset from
  * the kernel by just masking the top bits (which are all ones for a
  * kernel address).
+ *
+ * ARMv8.1 (using VHE) does have a TTBR1_EL2, and doesn't use these
+ * macros (the entire kernel runs at EL2).
  */
 #define HYP_PAGE_OFFSET_SHIFT	VA_BITS
 #define HYP_PAGE_OFFSET_MASK	((UL(1) << HYP_PAGE_OFFSET_SHIFT) - 1)
@@ -56,12 +59,19 @@
 
 #ifdef __ASSEMBLY__
 
+#include <asm/alternative.h>
+#include <asm/cpufeature.h>
+
 /*
  * Convert a kernel VA into a HYP VA.
  * reg: VA to be converted.
  */
 .macro kern_hyp_va	reg
+alternative_if_not ARM64_HAS_VIRT_HOST_EXTN	
 	and	\reg, \reg, #HYP_PAGE_OFFSET_MASK
+alternative_else
+	nop
+alternative_endif
 .endm
 
 #else

arch/arm64/kvm/hyp/hyp.h

@@ -25,9 +25,28 @@
 
 #define __hyp_text __section(.hyp.text) notrace
 
-#define kern_hyp_va(v) (typeof(v))((unsigned long)(v) & HYP_PAGE_OFFSET_MASK)
-#define hyp_kern_va(v) (typeof(v))((unsigned long)(v) - HYP_PAGE_OFFSET \
-						      + PAGE_OFFSET)
+static inline unsigned long __kern_hyp_va(unsigned long v)
+{
+	asm volatile(ALTERNATIVE("and %0, %0, %1",
+				 "nop",
+				 ARM64_HAS_VIRT_HOST_EXTN)
+		     : "+r" (v) : "i" (HYP_PAGE_OFFSET_MASK));
+	return v;
+}
+
+#define kern_hyp_va(v) (typeof(v))(__kern_hyp_va((unsigned long)(v)))
+
+static inline unsigned long __hyp_kern_va(unsigned long v)
+{
+	u64 offset = PAGE_OFFSET - HYP_PAGE_OFFSET;
+	asm volatile(ALTERNATIVE("add %0, %0, %1",
+				 "nop",
+				 ARM64_HAS_VIRT_HOST_EXTN)
+		     : "+r" (v) : "r" (offset));
+	return v;
+}
+
+#define hyp_kern_va(v) (typeof(v))(__hyp_kern_va((unsigned long)(v)))
 
 /**
  * hyp_alternate_select - Generates patchable code sequences that are