[PATCH v2 09/20] KVM: TDX: Handle TDX PV rdmsr/wrmsr hypercall

Binbin Wu
2025-02-27T01:19:19Z

Morph PV RDMSR/WRMSR hypercall to EXIT_REASON_MSR_{READ,WRITE} and
wire up KVM backend functions.

For complete_emulated_msr() callback, instead of injecting #GP on error,
implement tdx_complete_emulated_msr() to set return code on error. Also
set return value on MSR read according to the values from kvm x86
registers.

Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
Signed-off-by: Binbin Wu <binbin.wu@linux.intel.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
---
TDX "the rest" v2:
- Morph PV RDMSR/WRMSR hypercall to EXIT_REASON_MSR_{READ,WRITE}. (Sean)
- Rebased to use tdcall_to_vmx_exit_reason().
- Marshall values to the appropriate x86 registers to leverage the existing
kvm_emulate_{rdmsr,wrmsr}(). (Sean)
- Implement complete_emulated_msr() callback for TDX to set return value
and return code to vp_enter_args.
- Update changelog.

TDX "the rest" v1:
- Use TDVMCALL_STATUS prefix for TDX call status codes (Binbin)
---
arch/x86/kvm/vmx/main.c | 10 +++++++++-
arch/x86/kvm/vmx/tdx.c | 24 ++++++++++++++++++++++++
arch/x86/kvm/vmx/tdx.h | 2 ++
3 files changed, 35 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/vmx/main.c b/arch/x86/kvm/vmx/main.c
index 463de3add3bd..7f3be1b65ce1 100644
--- a/arch/x86/kvm/vmx/main.c
+++ b/arch/x86/kvm/vmx/main.c
@@ -235,6 +235,14 @@ static void vt_msr_filter_changed(struct kvm_vcpu *vcpu)
vmx_msr_filter_changed(vcpu);
}

+static int vt_complete_emulated_msr(struct kvm_vcpu *vcpu, int err)
+{
+ if (is_td_vcpu(vcpu))
+ return tdx_complete_emulated_msr(vcpu, err);
+
+ return kvm_complete_insn_gp(vcpu, err);
+}
+
#ifdef CONFIG_KVM_SMM
static int vt_smi_allowed(struct kvm_vcpu *vcpu, bool for_injection)
{
@@ -686,7 +694,7 @@ struct kvm_x86_ops vt_x86_ops __initdata = {
.migrate_timers = vmx_migrate_timers,

.msr_filter_changed = vt_msr_filter_changed,
- .complete_emulated_msr = kvm_complete_insn_gp,
+ .complete_emulated_msr = vt_complete_emulated_msr,

.vcpu_deliver_sipi_vector = kvm_vcpu_deliver_sipi_vector,

diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
index 5b556af0f139..85ff6e040cf3 100644
--- a/arch/x86/kvm/vmx/tdx.c
+++ b/arch/x86/kvm/vmx/tdx.c
@@ -878,6 +878,8 @@ static __always_inline u32 tdcall_to_vmx_exit_reason(struct kvm_vcpu *vcpu)
case EXIT_REASON_CPUID:
case EXIT_REASON_HLT:
case EXIT_REASON_IO_INSTRUCTION:
+ case EXIT_REASON_MSR_READ:
+ case EXIT_REASON_MSR_WRITE:
return tdvmcall_leaf(vcpu);
case EXIT_REASON_EPT_VIOLATION:
return EXIT_REASON_EPT_MISCONFIG;
@@ -1880,6 +1882,20 @@ static int tdx_handle_ept_violation(struct kvm_vcpu *vcpu)
return ret;
}

+int tdx_complete_emulated_msr(struct kvm_vcpu *vcpu, int err)
+{
+ if (err) {
+ tdvmcall_set_return_code(vcpu, TDVMCALL_STATUS_INVALID_OPERAND);
+ return 1;
+ }
+
+ if (vmx_get_exit_reason(vcpu).basic == EXIT_REASON_MSR_READ)
+ tdvmcall_set_return_val(vcpu, kvm_read_edx_eax(vcpu));
+
+ return 1;
+}
+
+
int tdx_handle_exit(struct kvm_vcpu *vcpu, fastpath_t fastpath)
{
struct vcpu_tdx *tdx = to_tdx(vcpu);
@@ -1945,6 +1961,14 @@ int tdx_handle_exit(struct kvm_vcpu *vcpu, fastpath_t fastpath)
return tdx_emulate_vmcall(vcpu);
case EXIT_REASON_IO_INSTRUCTION:
return tdx_emulate_io(vcpu);
+ case EXIT_REASON_MSR_READ:
+ kvm_rcx_write(vcpu, tdx->vp_enter_args.r12);
+ return kvm_emulate_rdmsr(vcpu);
+ case EXIT_REASON_MSR_WRITE:
+ kvm_rcx_write(vcpu, tdx->vp_enter_args.r12);
+ kvm_rax_write(vcpu, tdx->vp_enter_args.r13 & -1u);
+ kvm_rdx_write(vcpu, tdx->vp_enter_args.r13 >> 32);
+ return kvm_emulate_wrmsr(vcpu);
case EXIT_REASON_EPT_MISCONFIG:
return tdx_emulate_mmio(vcpu);
case EXIT_REASON_EPT_VIOLATION:
diff --git a/arch/x86/kvm/vmx/tdx.h b/arch/x86/kvm/vmx/tdx.h
index cb9014b7a4f1..8f8070d0f55e 100644
--- a/arch/x86/kvm/vmx/tdx.h
+++ b/arch/x86/kvm/vmx/tdx.h
@@ -171,6 +171,7 @@ static __always_inline void td_##lclass##_clearbit##bits(struct vcpu_tdx *tdx, \

bool tdx_interrupt_allowed(struct kvm_vcpu *vcpu);
+int tdx_complete_emulated_msr(struct kvm_vcpu *vcpu, int err);

TDX_BUILD_TDVPS_ACCESSORS(16, VMCS, vmcs);
TDX_BUILD_TDVPS_ACCESSORS(32, VMCS, vmcs);
@@ -194,6 +195,7 @@ struct vcpu_tdx {
};

static inline bool tdx_interrupt_allowed(struct kvm_vcpu *vcpu) { return false; }
+static inline int tdx_complete_emulated_msr(struct kvm_vcpu *vcpu, int err) { return 0; }

#endif

--
2.46.0