linux-kernel - [PATCH v2 3/4] KVM: VMX: Support the immediate form WRMSRNS in fastpath

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Message-ID: <20250802001520.3142577-4-xin@zytor.com>
Date: Fri,  1 Aug 2025 17:15:19 -0700
From: "Xin Li (Intel)" <xin@...or.com>
To: linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc: pbonzini@...hat.com, seanjc@...gle.com, tglx@...utronix.de,
        mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com,
        x86@...nel.org, hpa@...or.com, xin@...or.com, chao.gao@...el.com
Subject: [PATCH v2 3/4] KVM: VMX: Support the immediate form WRMSRNS in fastpath

Refactored handle_fastpath_set_msr_irqoff() to accept MSR index and data
directly via input arguments, enabling it to handle both implicit and
immediate form WRMSRNS through appropriate wrappers.  Also rename it to
__handle_fastpath_wrmsr().

BTW, per Sean's suggestion, rename handle_fastpath_set_msr_irqoff() to
handle_fastpath_wrmsr().

Signed-off-by: Xin Li (Intel) <xin@...or.com>
---

Change in v2:
*) Moved fastpath support in a separate patch (Sean).
---
 arch/x86/kvm/svm/svm.c |  2 +-
 arch/x86/kvm/vmx/vmx.c |  5 ++++-
 arch/x86/kvm/x86.c     | 19 +++++++++++++------
 arch/x86/kvm/x86.h     |  3 ++-
 4 files changed, 20 insertions(+), 9 deletions(-)

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index d9931c6c4bc6..4abc34b7c2c7 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -4189,7 +4189,7 @@ static fastpath_t svm_exit_handlers_fastpath(struct kvm_vcpu *vcpu)
 	case SVM_EXIT_MSR:
 		if (!svm->vmcb->control.exit_info_1)
 			break;
-		return handle_fastpath_set_msr_irqoff(vcpu);
+		return handle_fastpath_wrmsr(vcpu);
 	case SVM_EXIT_HLT:
 		return handle_fastpath_hlt(vcpu);
 	default:
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index c112595dfff9..2cd865e117a8 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -7191,7 +7191,10 @@ static fastpath_t vmx_exit_handlers_fastpath(struct kvm_vcpu *vcpu,
 
 	switch (vmx_get_exit_reason(vcpu).basic) {
 	case EXIT_REASON_MSR_WRITE:
-		return handle_fastpath_set_msr_irqoff(vcpu);
+		return handle_fastpath_wrmsr(vcpu);
+	case EXIT_REASON_MSR_WRITE_IMM:
+		return handle_fastpath_wrmsr_imm(vcpu, vmx_get_exit_qual(vcpu),
+						 vmx_get_msr_imm_reg());
 	case EXIT_REASON_PREEMPTION_TIMER:
 		return handle_fastpath_preemption_timer(vcpu, force_immediate_exit);
 	case EXIT_REASON_HLT:
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index fe12aae7089c..9aede349b6ec 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2202,10 +2202,8 @@ static int handle_fastpath_set_tscdeadline(struct kvm_vcpu *vcpu, u64 data)
 	return 0;
 }
 
-fastpath_t handle_fastpath_set_msr_irqoff(struct kvm_vcpu *vcpu)
+static fastpath_t __handle_fastpath_wrmsr(struct kvm_vcpu *vcpu, u32 msr, u64 data)
 {
-	u32 msr = kvm_rcx_read(vcpu);
-	u64 data;
 	fastpath_t ret;
 	bool handled;
 
@@ -2213,11 +2211,9 @@ fastpath_t handle_fastpath_set_msr_irqoff(struct kvm_vcpu *vcpu)
 
 	switch (msr) {
 	case APIC_BASE_MSR + (APIC_ICR >> 4):
-		data = kvm_read_edx_eax(vcpu);
 		handled = !handle_fastpath_set_x2apic_icr_irqoff(vcpu, data);
 		break;
 	case MSR_IA32_TSC_DEADLINE:
-		data = kvm_read_edx_eax(vcpu);
 		handled = !handle_fastpath_set_tscdeadline(vcpu, data);
 		break;
 	default:
@@ -2239,7 +2235,18 @@ fastpath_t handle_fastpath_set_msr_irqoff(struct kvm_vcpu *vcpu)
 
 	return ret;
 }
-EXPORT_SYMBOL_GPL(handle_fastpath_set_msr_irqoff);
+
+fastpath_t handle_fastpath_wrmsr(struct kvm_vcpu *vcpu)
+{
+	return __handle_fastpath_wrmsr(vcpu, kvm_rcx_read(vcpu), kvm_read_edx_eax(vcpu));
+}
+EXPORT_SYMBOL_GPL(handle_fastpath_wrmsr);
+
+fastpath_t handle_fastpath_wrmsr_imm(struct kvm_vcpu *vcpu, u32 msr, int reg)
+{
+	return __handle_fastpath_wrmsr(vcpu, msr, kvm_register_read(vcpu, reg));
+}
+EXPORT_SYMBOL_GPL(handle_fastpath_wrmsr_imm);
 
 /*
  * Adapt set_msr() to msr_io()'s calling convention
diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
index bcfd9b719ada..de22c19b47fe 100644
--- a/arch/x86/kvm/x86.h
+++ b/arch/x86/kvm/x86.h
@@ -437,7 +437,8 @@ int x86_decode_emulated_instruction(struct kvm_vcpu *vcpu, int emulation_type,
 				    void *insn, int insn_len);
 int x86_emulate_instruction(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
 			    int emulation_type, void *insn, int insn_len);
-fastpath_t handle_fastpath_set_msr_irqoff(struct kvm_vcpu *vcpu);
+fastpath_t handle_fastpath_wrmsr(struct kvm_vcpu *vcpu);
+fastpath_t handle_fastpath_wrmsr_imm(struct kvm_vcpu *vcpu, u32 msr, int reg);
 fastpath_t handle_fastpath_hlt(struct kvm_vcpu *vcpu);
 
 extern struct kvm_caps kvm_caps;
-- 
2.50.1