x86/hyperv: Fix hv_get/set_register for nested bringup

hv_get_nested_reg only translates SINT0, resulting in the wrong sint
being registered by nested vmbus.

Fix the issue with new utility function hv_is_sint_reg.

While at it, improve clarity of hv_set_non_nested_register and hv_is_synic_reg.
Signed-off-by: Nuno Das Neves <nunodasneves@linux.microsoft.com>
Reviewed-by: Jinank Jain <jinankjain@linux.microsoft.com>
Link: https://lore.kernel.org/r/1675980172-6851-1-git-send-email-nunodasneves@linux.microsoft.comSigned-off-by: Wei Liu <wei.liu@kernel.org>

arch/x86/include/asm/mshyperv.h

@@ -224,10 +224,14 @@ extern bool hv_isolation_type_snp(void);
 
 static inline bool hv_is_synic_reg(unsigned int reg)
 {
-	if ((reg >= HV_REGISTER_SCONTROL) &&
-	    (reg <= HV_REGISTER_SINT15))
-		return true;
-	return false;
+	return (reg >= HV_REGISTER_SCONTROL) &&
+	       (reg <= HV_REGISTER_SINT15);
+}
+
+static inline bool hv_is_sint_reg(unsigned int reg)
+{
+	return (reg >= HV_REGISTER_SINT0) &&
+	       (reg <= HV_REGISTER_SINT15);
 }
 
 u64 hv_get_register(unsigned int reg);

arch/x86/kernel/cpu/mshyperv.c

@@ -44,6 +44,9 @@ struct ms_hyperv_info ms_hyperv;
 #if IS_ENABLED(CONFIG_HYPERV)
 static inline unsigned int hv_get_nested_reg(unsigned int reg)
 {
+	if (hv_is_sint_reg(reg))
+		return reg - HV_REGISTER_SINT0 + HV_REGISTER_NESTED_SINT0;
+
 	switch (reg) {
 	case HV_REGISTER_SIMP:
 		return HV_REGISTER_NESTED_SIMP;
@@ -53,8 +56,6 @@ static inline unsigned int hv_get_nested_reg(unsigned int reg)
 		return HV_REGISTER_NESTED_SVERSION;
 	case HV_REGISTER_SCONTROL:
 		return HV_REGISTER_NESTED_SCONTROL;
-	case HV_REGISTER_SINT0:
-		return HV_REGISTER_NESTED_SINT0;
 	case HV_REGISTER_EOM:
 		return HV_REGISTER_NESTED_EOM;
 	default:
@@ -80,8 +81,7 @@ void hv_set_non_nested_register(unsigned int reg, u64 value)
 		hv_ghcb_msr_write(reg, value);
 
 		/* Write proxy bit via wrmsl instruction */
-		if (reg >= HV_REGISTER_SINT0 &&
-		    reg <= HV_REGISTER_SINT15)
+		if (hv_is_sint_reg(reg))
 			wrmsrl(reg, value | 1 << 20);
 	} else {
 		wrmsrl(reg, value);