Re: [PATCH 01/21] KVM: x86: Split core of hypercall emulation to helper function

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On 2/28/2024 7:20 AM, Paolo Bonzini wrote:
From: Sean Christopherson <seanjc@xxxxxxxxxx>

By necessity, TDX will use a different register ABI for hypercalls.
Break out the core functionality so that it may be reused for TDX.

Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
Signed-off-by: Isaku Yamahata <isaku.yamahata@xxxxxxxxx>
Message-Id: <5134caa55ac3dec33fb2addb5545b52b3b52db02.1705965635.git.isaku.yamahata@xxxxxxxxx>
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>

Reviewed-by: Binbin Wu <binbin.wu@xxxxxxxxxxxxxxx>

---
  arch/x86/include/asm/kvm_host.h |  4 +++
  arch/x86/kvm/x86.c              | 56 ++++++++++++++++++++++-----------
  2 files changed, 42 insertions(+), 18 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 724a0c778f79..85dc0f7d09e3 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -2133,6 +2133,10 @@ static inline void kvm_clear_apicv_inhibit(struct kvm *kvm,
  	kvm_set_or_clear_apicv_inhibit(kvm, reason, false);
  }
+unsigned long __kvm_emulate_hypercall(struct kvm_vcpu *vcpu, unsigned long nr,
+				      unsigned long a0, unsigned long a1,
+				      unsigned long a2, unsigned long a3,
+				      int op_64_bit, int cpl);
  int kvm_emulate_hypercall(struct kvm_vcpu *vcpu);
int kvm_mmu_page_fault(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa, u64 error_code,
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index b9dfe3179332..f10a5a617120 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -10046,26 +10046,15 @@ static int complete_hypercall_exit(struct kvm_vcpu *vcpu)
  	return kvm_skip_emulated_instruction(vcpu);
  }
-int kvm_emulate_hypercall(struct kvm_vcpu *vcpu)
+unsigned long __kvm_emulate_hypercall(struct kvm_vcpu *vcpu, unsigned long nr,
+				      unsigned long a0, unsigned long a1,
+				      unsigned long a2, unsigned long a3,
+				      int op_64_bit, int cpl)
  {
-	unsigned long nr, a0, a1, a2, a3, ret;
-	int op_64_bit;
-
-	if (kvm_xen_hypercall_enabled(vcpu->kvm))
-		return kvm_xen_hypercall(vcpu);
-
-	if (kvm_hv_hypercall_enabled(vcpu))
-		return kvm_hv_hypercall(vcpu);
-
-	nr = kvm_rax_read(vcpu);
-	a0 = kvm_rbx_read(vcpu);
-	a1 = kvm_rcx_read(vcpu);
-	a2 = kvm_rdx_read(vcpu);
-	a3 = kvm_rsi_read(vcpu);
+	unsigned long ret;
trace_kvm_hypercall(nr, a0, a1, a2, a3); - op_64_bit = is_64_bit_hypercall(vcpu);
  	if (!op_64_bit) {
  		nr &= 0xFFFFFFFF;
  		a0 &= 0xFFFFFFFF;
@@ -10074,7 +10063,7 @@ int kvm_emulate_hypercall(struct kvm_vcpu *vcpu)
  		a3 &= 0xFFFFFFFF;
  	}
- if (static_call(kvm_x86_get_cpl)(vcpu) != 0) {
+	if (cpl) {
  		ret = -KVM_EPERM;
  		goto out;
  	}
@@ -10135,18 +10124,49 @@ int kvm_emulate_hypercall(struct kvm_vcpu *vcpu)
WARN_ON_ONCE(vcpu->run->hypercall.flags & KVM_EXIT_HYPERCALL_MBZ);
  		vcpu->arch.complete_userspace_io = complete_hypercall_exit;
+		/* stat is incremented on completion. */
  		return 0;
  	}
  	default:
  		ret = -KVM_ENOSYS;
  		break;
  	}
+
  out:
+	++vcpu->stat.hypercalls;
+	return ret;
+}
+EXPORT_SYMBOL_GPL(__kvm_emulate_hypercall);
+
+int kvm_emulate_hypercall(struct kvm_vcpu *vcpu)
+{
+	unsigned long nr, a0, a1, a2, a3, ret;
+	int op_64_bit;
+	int cpl;
+
+	if (kvm_xen_hypercall_enabled(vcpu->kvm))
+		return kvm_xen_hypercall(vcpu);
+
+	if (kvm_hv_hypercall_enabled(vcpu))
+		return kvm_hv_hypercall(vcpu);
+
+	nr = kvm_rax_read(vcpu);
+	a0 = kvm_rbx_read(vcpu);
+	a1 = kvm_rcx_read(vcpu);
+	a2 = kvm_rdx_read(vcpu);
+	a3 = kvm_rsi_read(vcpu);
+	op_64_bit = is_64_bit_hypercall(vcpu);
+	cpl = static_call(kvm_x86_get_cpl)(vcpu);
+
+	ret = __kvm_emulate_hypercall(vcpu, nr, a0, a1, a2, a3, op_64_bit, cpl);
+	if (nr == KVM_HC_MAP_GPA_RANGE && !ret)
+		/* MAP_GPA tosses the request to the user space. */
+		return 0;
+
  	if (!op_64_bit)
  		ret = (u32)ret;
  	kvm_rax_write(vcpu, ret);
- ++vcpu->stat.hypercalls;
  	return kvm_skip_emulated_instruction(vcpu);
  }
  EXPORT_SYMBOL_GPL(kvm_emulate_hypercall);





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