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Message-ID: <20250730174605.1614792-3-xin@zytor.com>
Date: Wed, 30 Jul 2025 10:46:03 -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 v1 2/4] KVM: x86: Introduce MSR read/write emulation helpers
Add helper functions to centralize guest MSR read and write emulation.
This change consolidates the MSR emulation logic and makes it easier
to extend support for new MSR-related VM exit reasons introduced with
the immediate form of MSR instructions.
Signed-off-by: Xin Li (Intel) <xin@...or.com>
---
arch/x86/include/asm/kvm_host.h | 1 +
arch/x86/kvm/x86.c | 67 +++++++++++++++++++++++----------
2 files changed, 49 insertions(+), 19 deletions(-)
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index f19a76d3ca0e..a854d9a166fe 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -201,6 +201,7 @@ enum kvm_reg {
VCPU_EXREG_SEGMENTS,
VCPU_EXREG_EXIT_INFO_1,
VCPU_EXREG_EXIT_INFO_2,
+ VCPU_EXREG_EDX_EAX,
};
enum {
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index a1c49bc681c4..5086c3b30345 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2024,54 +2024,71 @@ static int kvm_msr_user_space(struct kvm_vcpu *vcpu, u32 index,
return 1;
}
-int kvm_emulate_rdmsr(struct kvm_vcpu *vcpu)
+static int kvm_emulate_get_msr(struct kvm_vcpu *vcpu, u32 msr, int reg)
{
- u32 ecx = kvm_rcx_read(vcpu);
u64 data;
int r;
- r = kvm_get_msr_with_filter(vcpu, ecx, &data);
+ r = kvm_get_msr_with_filter(vcpu, msr, &data);
if (!r) {
- trace_kvm_msr_read(ecx, data);
+ trace_kvm_msr_read(msr, data);
- kvm_rax_write(vcpu, data & -1u);
- kvm_rdx_write(vcpu, (data >> 32) & -1u);
+ if (reg == VCPU_EXREG_EDX_EAX) {
+ kvm_rax_write(vcpu, data & -1u);
+ kvm_rdx_write(vcpu, (data >> 32) & -1u);
+ } else {
+ kvm_register_write(vcpu, reg, data);
+ }
} else {
/* MSR read failed? See if we should ask user space */
- if (kvm_msr_user_space(vcpu, ecx, KVM_EXIT_X86_RDMSR, 0,
+ if (kvm_msr_user_space(vcpu, msr, KVM_EXIT_X86_RDMSR, 0,
complete_fast_rdmsr, r))
return 0;
- trace_kvm_msr_read_ex(ecx);
+ trace_kvm_msr_read_ex(msr);
}
return kvm_x86_call(complete_emulated_msr)(vcpu, r);
}
+
+int kvm_emulate_rdmsr(struct kvm_vcpu *vcpu)
+{
+ return kvm_emulate_get_msr(vcpu, kvm_rcx_read(vcpu), VCPU_EXREG_EDX_EAX);
+}
EXPORT_SYMBOL_GPL(kvm_emulate_rdmsr);
-int kvm_emulate_wrmsr(struct kvm_vcpu *vcpu)
+static int kvm_emulate_set_msr(struct kvm_vcpu *vcpu, u32 msr, int reg)
{
- u32 ecx = kvm_rcx_read(vcpu);
- u64 data = kvm_read_edx_eax(vcpu);
+ u64 data;
int r;
- r = kvm_set_msr_with_filter(vcpu, ecx, data);
+ if (reg == VCPU_EXREG_EDX_EAX)
+ data = kvm_read_edx_eax(vcpu);
+ else
+ data = kvm_register_read(vcpu, reg);
+
+ r = kvm_set_msr_with_filter(vcpu, msr, data);
if (!r) {
- trace_kvm_msr_write(ecx, data);
+ trace_kvm_msr_write(msr, data);
} else {
/* MSR write failed? See if we should ask user space */
- if (kvm_msr_user_space(vcpu, ecx, KVM_EXIT_X86_WRMSR, data,
+ if (kvm_msr_user_space(vcpu, msr, KVM_EXIT_X86_WRMSR, data,
complete_fast_msr_access, r))
return 0;
/* Signal all other negative errors to userspace */
if (r < 0)
return r;
- trace_kvm_msr_write_ex(ecx, data);
+ trace_kvm_msr_write_ex(msr, data);
}
return kvm_x86_call(complete_emulated_msr)(vcpu, r);
}
+
+int kvm_emulate_wrmsr(struct kvm_vcpu *vcpu)
+{
+ return kvm_emulate_set_msr(vcpu, kvm_rcx_read(vcpu), VCPU_EXREG_EDX_EAX);
+}
EXPORT_SYMBOL_GPL(kvm_emulate_wrmsr);
int kvm_emulate_as_nop(struct kvm_vcpu *vcpu)
@@ -2163,9 +2180,8 @@ 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_set_msr_irqoff(struct kvm_vcpu *vcpu, u32 msr, int reg)
{
- u32 msr = kvm_rcx_read(vcpu);
u64 data;
fastpath_t ret;
bool handled;
@@ -2174,11 +2190,19 @@ 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);
+ if (reg == VCPU_EXREG_EDX_EAX)
+ data = kvm_read_edx_eax(vcpu);
+ else
+ data = kvm_register_read(vcpu, reg);
+
handled = !handle_fastpath_set_x2apic_icr_irqoff(vcpu, data);
break;
case MSR_IA32_TSC_DEADLINE:
- data = kvm_read_edx_eax(vcpu);
+ if (reg == VCPU_EXREG_EDX_EAX)
+ data = kvm_read_edx_eax(vcpu);
+ else
+ data = kvm_register_read(vcpu, reg);
+
handled = !handle_fastpath_set_tscdeadline(vcpu, data);
break;
default:
@@ -2200,6 +2224,11 @@ fastpath_t handle_fastpath_set_msr_irqoff(struct kvm_vcpu *vcpu)
return ret;
}
+
+fastpath_t handle_fastpath_set_msr_irqoff(struct kvm_vcpu *vcpu)
+{
+ return handle_set_msr_irqoff(vcpu, kvm_rcx_read(vcpu), VCPU_EXREG_EDX_EAX);
+}
EXPORT_SYMBOL_GPL(handle_fastpath_set_msr_irqoff);
/*
--
2.50.1
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