linux-kernel - [PATCH] LoongArch: KVM: Add hypercall service support for usermode VMM

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Message-Id: <20241223084212.34822-1-maobibo@loongson.cn>
Date: Mon, 23 Dec 2024 16:42:12 +0800
From: Bibo Mao <maobibo@...ngson.cn>
To: Tianrui Zhao <zhaotianrui@...ngson.cn>,
	Huacai Chen <chenhuacai@...nel.org>
Cc: WANG Xuerui <kernel@...0n.name>,
	kvm@...r.kernel.org,
	loongarch@...ts.linux.dev,
	linux-kernel@...r.kernel.org
Subject: [PATCH] LoongArch: KVM: Add hypercall service support for usermode VMM

Some VMMs provides special hypercall service in usermode, KVM need
not handle the usermode hypercall service and pass it to VMM and
let VMM handle it.

Here new code KVM_HCALL_CODE_USER is added for user-mode hypercall
service, KVM loads all six registers to VMM.

Signed-off-by: Bibo Mao <maobibo@...ngson.cn>
---
 arch/loongarch/include/asm/kvm_host.h      |  1 +
 arch/loongarch/include/asm/kvm_para.h      |  2 ++
 arch/loongarch/include/uapi/asm/kvm_para.h |  1 +
 arch/loongarch/kvm/exit.c                  | 22 ++++++++++++++++++++++
 arch/loongarch/kvm/vcpu.c                  |  3 +++
 5 files changed, 29 insertions(+)

diff --git a/arch/loongarch/include/asm/kvm_host.h b/arch/loongarch/include/asm/kvm_host.h
index 7b8367c39da8..590982cd986e 100644
--- a/arch/loongarch/include/asm/kvm_host.h
+++ b/arch/loongarch/include/asm/kvm_host.h
@@ -162,6 +162,7 @@ enum emulation_result {
 #define LOONGARCH_PV_FEAT_UPDATED	BIT_ULL(63)
 #define LOONGARCH_PV_FEAT_MASK		(BIT(KVM_FEATURE_IPI) |		\
 					 BIT(KVM_FEATURE_STEAL_TIME) |	\
+					 BIT(KVM_FEATURE_USER_HCALL) |	\
 					 BIT(KVM_FEATURE_VIRT_EXTIOI))
 
 struct kvm_vcpu_arch {
diff --git a/arch/loongarch/include/asm/kvm_para.h b/arch/loongarch/include/asm/kvm_para.h
index c4e84227280d..d3c00de484f6 100644
--- a/arch/loongarch/include/asm/kvm_para.h
+++ b/arch/loongarch/include/asm/kvm_para.h
@@ -13,12 +13,14 @@
 
 #define KVM_HCALL_CODE_SERVICE		0
 #define KVM_HCALL_CODE_SWDBG		1
+#define KVM_HCALL_CODE_USER		2
 
 #define KVM_HCALL_SERVICE		HYPERCALL_ENCODE(HYPERVISOR_KVM, KVM_HCALL_CODE_SERVICE)
 #define  KVM_HCALL_FUNC_IPI		1
 #define  KVM_HCALL_FUNC_NOTIFY		2
 
 #define KVM_HCALL_SWDBG			HYPERCALL_ENCODE(HYPERVISOR_KVM, KVM_HCALL_CODE_SWDBG)
+#define KVM_HCALL_USER_SERVICE		HYPERCALL_ENCODE(HYPERVISOR_KVM, KVM_HCALL_CODE_USER)
 
 /*
  * LoongArch hypercall return code
diff --git a/arch/loongarch/include/uapi/asm/kvm_para.h b/arch/loongarch/include/uapi/asm/kvm_para.h
index b0604aa9b4bb..76d802ef01ce 100644
--- a/arch/loongarch/include/uapi/asm/kvm_para.h
+++ b/arch/loongarch/include/uapi/asm/kvm_para.h
@@ -17,5 +17,6 @@
 #define  KVM_FEATURE_STEAL_TIME		2
 /* BIT 24 - 31 are features configurable by user space vmm */
 #define  KVM_FEATURE_VIRT_EXTIOI	24
+#define  KVM_FEATURE_USER_HCALL		25
 
 #endif /* _UAPI_ASM_KVM_PARA_H */
diff --git a/arch/loongarch/kvm/exit.c b/arch/loongarch/kvm/exit.c
index a7893bd01e73..1a85cd4fb6a5 100644
--- a/arch/loongarch/kvm/exit.c
+++ b/arch/loongarch/kvm/exit.c
@@ -873,6 +873,28 @@ static int kvm_handle_hypercall(struct kvm_vcpu *vcpu)
 		vcpu->stat.hypercall_exits++;
 		kvm_handle_service(vcpu);
 		break;
+	case KVM_HCALL_USER_SERVICE:
+		if (!kvm_guest_has_pv_feature(vcpu, KVM_FEATURE_USER_HCALL)) {
+			kvm_write_reg(vcpu, LOONGARCH_GPR_A0, KVM_HCALL_INVALID_CODE);
+			break;
+		}
+
+		vcpu->run->exit_reason = KVM_EXIT_HYPERCALL;
+		vcpu->run->hypercall.nr = KVM_HCALL_USER_SERVICE;
+		vcpu->run->hypercall.args[0] = kvm_read_reg(vcpu, LOONGARCH_GPR_A0);
+		vcpu->run->hypercall.args[1] = kvm_read_reg(vcpu, LOONGARCH_GPR_A1);
+		vcpu->run->hypercall.args[2] = kvm_read_reg(vcpu, LOONGARCH_GPR_A2);
+		vcpu->run->hypercall.args[3] = kvm_read_reg(vcpu, LOONGARCH_GPR_A3);
+		vcpu->run->hypercall.args[4] = kvm_read_reg(vcpu, LOONGARCH_GPR_A4);
+		vcpu->run->hypercall.args[5] = kvm_read_reg(vcpu, LOONGARCH_GPR_A5);
+		vcpu->run->hypercall.flags = 0;
+		/*
+		 * Set invalid return value by default
+		 * Need user-mode VMM modify it
+		 */
+		vcpu->run->hypercall.ret = KVM_HCALL_INVALID_CODE;
+		ret = RESUME_HOST;
+		break;
 	case KVM_HCALL_SWDBG:
 		/* KVM_HCALL_SWDBG only in effective when SW_BP is enabled */
 		if (vcpu->guest_debug & KVM_GUESTDBG_SW_BP_MASK) {
diff --git a/arch/loongarch/kvm/vcpu.c b/arch/loongarch/kvm/vcpu.c
index d18a4a270415..8c46ad1872ee 100644
--- a/arch/loongarch/kvm/vcpu.c
+++ b/arch/loongarch/kvm/vcpu.c
@@ -1735,6 +1735,9 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu)
 	if (run->exit_reason == KVM_EXIT_LOONGARCH_IOCSR) {
 		if (!run->iocsr_io.is_write)
 			kvm_complete_iocsr_read(vcpu, run);
+	} else if (run->exit_reason == KVM_EXIT_HYPERCALL) {
+		kvm_write_reg(vcpu, LOONGARCH_GPR_A0, run->hypercall.ret);
+		update_pc(&vcpu->arch);
 	}
 
 	if (!vcpu->wants_to_run)

base-commit: 48f506ad0b683d3e7e794efa60c5785c4fdc86fa
-- 
2.39.3