[PATCH v6 3/7] LoongArch: KVM: Add cpucfg area for kvm hypervisor

[Bibo Mao <maobibo@loongson.cn>]

Instruction cpucfg can be used to get processor features. And there
is trap exception when it is executed in VM mode, and also it is
to provide cpu features to VM. On real hardware cpucfg area 0 - 20
is used.  Here one specified area 0x40000000 -- 0x400000ff is used
for KVM hypervisor to privide PV features, and the area can be extended
for other hypervisors in future. This area will never be used for
real HW, it is only used by software.

Signed-off-by: Bibo Mao <maobibo@loongson.cn>
---
 arch/loongarch/include/asm/inst.h      |  1 +
 arch/loongarch/include/asm/loongarch.h | 10 +++++
 arch/loongarch/kvm/exit.c              | 59 +++++++++++++++++++-------
 3 files changed, 54 insertions(+), 16 deletions(-)

diff --git a/arch/loongarch/include/asm/inst.h b/arch/loongarch/include/asm/inst.h
index d8f637f9e400..ad120f924905 100644
--- a/arch/loongarch/include/asm/inst.h
+++ b/arch/loongarch/include/asm/inst.h
@@ -67,6 +67,7 @@ enum reg2_op {
 	revhd_op	= 0x11,
 	extwh_op	= 0x16,
 	extwb_op	= 0x17,
+	cpucfg_op	= 0x1b,
 	iocsrrdb_op     = 0x19200,
 	iocsrrdh_op     = 0x19201,
 	iocsrrdw_op     = 0x19202,
diff --git a/arch/loongarch/include/asm/loongarch.h b/arch/loongarch/include/asm/loongarch.h
index 46366e783c84..a1d22e8b6f94 100644
--- a/arch/loongarch/include/asm/loongarch.h
+++ b/arch/loongarch/include/asm/loongarch.h
@@ -158,6 +158,16 @@
 #define  CPUCFG48_VFPU_CG		BIT(2)
 #define  CPUCFG48_RAM_CG		BIT(3)
 
+/*
+ * cpucfg index area: 0x40000000 -- 0x400000ff
+ * SW emulation for KVM hypervirsor
+ */
+#define CPUCFG_KVM_BASE			0x40000000UL
+#define CPUCFG_KVM_SIZE			0x100
+#define CPUCFG_KVM_SIG			CPUCFG_KVM_BASE
+#define  KVM_SIGNATURE			"KVM\0"
+#define CPUCFG_KVM_FEATURE		(CPUCFG_KVM_BASE + 4)
+
 #ifndef __ASSEMBLY__
 
 /* CSR */
diff --git a/arch/loongarch/kvm/exit.c b/arch/loongarch/kvm/exit.c
index 923bbca9bd22..a8d3b652d3ea 100644
--- a/arch/loongarch/kvm/exit.c
+++ b/arch/loongarch/kvm/exit.c
@@ -206,10 +206,50 @@ int kvm_emu_idle(struct kvm_vcpu *vcpu)
 	return EMULATE_DONE;
 }
 
-static int kvm_trap_handle_gspr(struct kvm_vcpu *vcpu)
+static int kvm_emu_cpucfg(struct kvm_vcpu *vcpu, larch_inst inst)
 {
 	int rd, rj;
 	unsigned int index;
+	unsigned long plv;
+
+	rd = inst.reg2_format.rd;
+	rj = inst.reg2_format.rj;
+	++vcpu->stat.cpucfg_exits;
+	index = vcpu->arch.gprs[rj];
+
+	/*
+	 * By LoongArch Reference Manual 2.2.10.5
+	 * Return value is 0 for undefined cpucfg index
+	 *
+	 * Disable preemption since hw gcsr is accessed
+	 */
+	preempt_disable();
+	plv = kvm_read_hw_gcsr(LOONGARCH_CSR_CRMD) >> CSR_CRMD_PLV_SHIFT;
+	switch (index) {
+	case 0 ... (KVM_MAX_CPUCFG_REGS - 1):
+		vcpu->arch.gprs[rd] = vcpu->arch.cpucfg[index];
+		break;
+	case CPUCFG_KVM_SIG:
+		/*
+		 * Cpucfg emulation between 0x40000000 -- 0x400000ff
+		 * Return value with 0 if executed in user mode
+		 */
+		if ((plv & CSR_CRMD_PLV) == PLV_KERN)
+			vcpu->arch.gprs[rd] = *(unsigned int *)KVM_SIGNATURE;
+		else
+			vcpu->arch.gprs[rd] = 0;
+		break;
+	default:
+		vcpu->arch.gprs[rd] = 0;
+		break;
+	}
+
+	preempt_enable();
+	return EMULATE_DONE;
+}
+
+static int kvm_trap_handle_gspr(struct kvm_vcpu *vcpu)
+{
 	unsigned long curr_pc;
 	larch_inst inst;
 	enum emulation_result er = EMULATE_DONE;
@@ -224,21 +264,8 @@ static int kvm_trap_handle_gspr(struct kvm_vcpu *vcpu)
 	er = EMULATE_FAIL;
 	switch (((inst.word >> 24) & 0xff)) {
 	case 0x0: /* CPUCFG GSPR */
-		if (inst.reg2_format.opcode == 0x1B) {
-			rd = inst.reg2_format.rd;
-			rj = inst.reg2_format.rj;
-			++vcpu->stat.cpucfg_exits;
-			index = vcpu->arch.gprs[rj];
-			er = EMULATE_DONE;
-			/*
-			 * By LoongArch Reference Manual 2.2.10.5
-			 * return value is 0 for undefined cpucfg index
-			 */
-			if (index < KVM_MAX_CPUCFG_REGS)
-				vcpu->arch.gprs[rd] = vcpu->arch.cpucfg[index];
-			else
-				vcpu->arch.gprs[rd] = 0;
-		}
+		if (inst.reg2_format.opcode == cpucfg_op)
+			er = kvm_emu_cpucfg(vcpu, inst);
 		break;
 	case 0x4: /* CSR{RD,WR,XCHG} GSPR */
 		er = kvm_handle_csr(vcpu, inst);
-- 
2.39.3