linux-kernel - [PATCH] LoongArch: KVM: Add cpucfg area for kvm hypervisor

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Date: Thu, 28 Dec 2023 20:21:38 +0800
From: Bibo Mao <maobibo@...ngson.cn>
To: Huacai Chen <chenhuacai@...nel.org>,
	Tianrui Zhao <zhaotianrui@...ngson.cn>
Cc: WANG Xuerui <kernel@...0n.name>,
	loongarch@...ts.linux.dev,
	linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org
Subject: [PATCH] LoongArch: KVM: Add cpucfg area for kvm hypervisor

VM will trap into hypervisor when executing cpucfg instruction. With
cpucfg instruction, address index is passed from register, so address
space is large enough. And now hardware only uses the area 0 - 20 for
actual usage, here one specified area 0x10000000 -- 0x100000ff is used
for KVM hypervisor, and the area can be extended for other hypervisors
in future.

Signed-off-by: Bibo Mao <maobibo@...ngson.cn>
---
 arch/loongarch/include/asm/inst.h      |  1 +
 arch/loongarch/include/asm/loongarch.h |  9 +++++
 arch/loongarch/kvm/exit.c              | 46 +++++++++++++++++---------
 3 files changed, 40 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..a03b466555a1 100644
--- a/arch/loongarch/include/asm/loongarch.h
+++ b/arch/loongarch/include/asm/loongarch.h
@@ -158,6 +158,15 @@
 #define  CPUCFG48_VFPU_CG		BIT(2)
 #define  CPUCFG48_RAM_CG		BIT(3)
 
+/*
+ * cpucfg index area: 0x10000000 -- 0x100000ff
+ * SW emulation for KVM hypervirsor
+ */
+#define CPUCFG_KVM_BASE			0x10000000UL
+#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 f453a3e40cab..a7da63ecc6ab 100644
--- a/arch/loongarch/kvm/exit.c
+++ b/arch/loongarch/kvm/exit.c
@@ -215,10 +215,37 @@ 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;
+
+	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
+	 */
+	switch (index) {
+	case 0 ... (KVM_MAX_CPUCFG_REGS - 1):
+		vcpu->arch.gprs[rd] = vcpu->arch.cpucfg[index];
+		break;
+	case CPUCFG_KVM_SIG:
+		vcpu->arch.gprs[rd] = *(unsigned int *)KVM_SIGNATURE;
+		break;
+	default:
+		vcpu->arch.gprs[rd] = 0;
+		break;
+	}
+
+	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;
@@ -233,21 +260,8 @@ 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