arm64: KVM: Refactor kern_hyp_va to deal with multiple offsets

As we move towards a selectable HYP VA range, it is obvious that
we don't want to test a variable to find out if we need to use
the bottom VA range, the top VA range, or use the address as is
(for VHE).

Instead, we can expand our current helper to generate the right
mask or nop with code patching. We default to using the top VA
space, with alternatives to switch to the bottom one or to nop
out the instructions.

Signed-off-by: Marc Zyngier <[e-mail]>
Signed-off-by: Christoffer Dall <[e-mail]>

arch/arm64/include/asm/kvm_hyp.h

···
 
 #define __hyp_text __section(.hyp.text) notrace
 
-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)))
-
 #define read_sysreg_elx(r,nvh,vh)					\
 	({								\
 		u64 reg;						\

arch/arm64/include/asm/kvm_mmu.h

···
 /*
  * Convert a kernel VA into a HYP VA.
  * reg: VA to be converted.
+ *
+ * This generates the following sequences:
+ * - High mask:
+ *		and x0, x0, #HYP_PAGE_OFFSET_HIGH_MASK
+ *		nop
+ * - Low mask:
+ *		and x0, x0, #HYP_PAGE_OFFSET_HIGH_MASK
+ *		and x0, x0, #HYP_PAGE_OFFSET_LOW_MASK
+ * - VHE:
+ *		nop
+ *		nop
+ *
+ * The "low mask" version works because the mask is a strict subset of
+ * the "high mask", hence performing the first mask for nothing.
+ * Should be completely invisible on any viable CPU.
  */
 .macro kern_hyp_va	reg
-alternative_if_not ARM64_HAS_VIRT_HOST_EXTN	
-	and	\reg, \reg, #HYP_PAGE_OFFSET_MASK
+alternative_if_not ARM64_HAS_VIRT_HOST_EXTN
+	and     \reg, \reg, #HYP_PAGE_OFFSET_HIGH_MASK
 alternative_else
 	nop
+alternative_endif
+alternative_if_not ARM64_HYP_OFFSET_LOW
+	nop
+alternative_else
+	and     \reg, \reg, #HYP_PAGE_OFFSET_LOW_MASK
 alternative_endif
 .endm
 
···
 #include <asm/mmu_context.h>
 #include <asm/pgtable.h>
 
-#define KERN_TO_HYP(kva)	((unsigned long)kva & HYP_PAGE_OFFSET_MASK)
+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_HIGH_MASK));
+	asm volatile(ALTERNATIVE("nop",
+				 "and %0, %0, %1",
+				 ARM64_HYP_OFFSET_LOW)
+		     : "+r" (v)
+		     : "i" (HYP_PAGE_OFFSET_LOW_MASK));
+	return v;
+}
+
+#define kern_hyp_va(v) 	(typeof(v))(__kern_hyp_va((unsigned long)(v)))
+#define KERN_TO_HYP(v)	kern_hyp_va(v)
 
 /*
  * We currently only support a 40bit IPA.