KVM: arm64: Register AArch64 system register entries with the sysreg xarray

In order to reduce the number of lookups that we have to perform
when handling a sysreg, register each AArch64 sysreg descriptor
with the global xarray. The index of the descriptor is stored
as a 10 bit field in the data word.

Subsequent patches will retrieve and use the stored index.

Reviewed-by: Joey Gouly <joey.gouly@arm.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20240214131827.2856277-15-maz@kernel.org
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>

arch/arm64/include/asm/kvm_host.h

@@ -1078,6 +1078,9 @@ int kvm_handle_cp10_id(struct kvm_vcpu *vcpu);
 void kvm_reset_sys_regs(struct kvm_vcpu *vcpu);
 
 int __init kvm_sys_reg_table_init(void);
+struct sys_reg_desc;
+int __init populate_sysreg_config(const struct sys_reg_desc *sr,
+				  unsigned int idx);
 int __init populate_nv_trap_config(void);
 
 bool lock_all_vcpus(struct kvm *kvm);

arch/arm64/kvm/emulate-nested.c

@@ -427,12 +427,14 @@ static const complex_condition_check ccc[] = {
  * [19:14]	bit number in the FGT register (6 bits)
  * [20]		trap polarity (1 bit)
  * [25:21]	FG filter (5 bits)
- * [62:26]	Unused (37 bits)
+ * [35:26]	Main SysReg table index (10 bits)
+ * [62:36]	Unused (27 bits)
  * [63]		RES0 - Must be zero, as lost on insertion in the xarray
  */
 #define TC_CGT_BITS	10
 #define TC_FGT_BITS	4
 #define TC_FGF_BITS	5
+#define TC_SRI_BITS	10
 
 union trap_config {
 	u64	val;
@@ -442,7 +444,8 @@ union trap_config {
 		unsigned long	bit:6;		 /* Bit number */
 		unsigned long	pol:1;		 /* Polarity */
 		unsigned long	fgf:TC_FGF_BITS; /* Fine Grained Filter */
-		unsigned long	unused:37;	 /* Unused, should be zero */
+		unsigned long	sri:TC_SRI_BITS; /* SysReg Index */
+		unsigned long	unused:27;	 /* Unused, should be zero */
 		unsigned long	mbz:1;		 /* Must Be Zero */
 	};
 };
@@ -1868,6 +1871,38 @@ check_mcb:
 	return ret;
 }
 
+int __init populate_sysreg_config(const struct sys_reg_desc *sr,
+				  unsigned int idx)
+{
+	union trap_config tc;
+	u32 encoding;
+	void *ret;
+
+	/*
+	 * 0 is a valid value for the index, but not for the storage.
+	 * We'll store (idx+1), so check against an offset'd limit.
+	 */
+	if (idx >= (BIT(TC_SRI_BITS) - 1)) {
+		kvm_err("sysreg %s (%d) out of range\n", sr->name, idx);
+		return -EINVAL;
+	}
+
+	encoding = sys_reg(sr->Op0, sr->Op1, sr->CRn, sr->CRm, sr->Op2);
+	tc = get_trap_config(encoding);
+
+	if (tc.sri) {
+		kvm_err("sysreg %s (%d) duplicate entry (%d)\n",
+			sr->name, idx - 1, tc.sri);
+		return -EINVAL;
+	}
+
+	tc.sri = idx + 1;
+	ret = xa_store(&sr_forward_xa, encoding,
+		       xa_mk_value(tc.val), GFP_KERNEL);
+
+	return xa_err(ret);
+}
+
 static enum trap_behaviour get_behaviour(struct kvm_vcpu *vcpu,
 					 const struct trap_bits *tb)
 {

arch/arm64/kvm/sys_regs.c

@@ -3972,6 +3972,7 @@ int __init kvm_sys_reg_table_init(void)
 	struct sys_reg_params params;
 	bool valid = true;
 	unsigned int i;
+	int ret = 0;
 
 	/* Make sure tables are unique and in order. */
 	valid &= check_sysreg_table(sys_reg_descs, ARRAY_SIZE(sys_reg_descs), false);
@@ -3995,5 +3996,13 @@ int __init kvm_sys_reg_table_init(void)
 	if (!first_idreg)
 		return -EINVAL;
 
-	return populate_nv_trap_config();
+	ret = populate_nv_trap_config();
+
+	for (i = 0; !ret && i < ARRAY_SIZE(sys_reg_descs); i++)
+		ret = populate_sysreg_config(sys_reg_descs + i, i);
+
+	for (i = 0; !ret && i < ARRAY_SIZE(sys_insn_descs); i++)
+		ret = populate_sysreg_config(sys_insn_descs + i, i);
+
+	return ret;
 }