[PATCH v5 4/8] KVM: nSVM: Propagate hardware DecodeAssist bytes to VMCB12

DecodeAssists provides instruction bytes for nested page faults and
intercepted page faults caused by data accesses.  When the feature is
exposed to L1, copy fresh hardware-provided instruction bytes from VMCB02
to VMCB12 for these exits.

Clear the VMCB12 instruction-byte state before rebuilding it, and leave the
length zero for instruction-fetch page faults, unrelated exits, and exits
without fresh hardware bytes.

Signed-off-by: Tina Zhang <[email protected]>
---
 arch/x86/kvm/svm/nested.c | 35 +++++++++++++++++++++++++++++++++++
 1 file changed, 35 insertions(+)

diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index 6770721d4e4c..2db0ec66e8dc 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -42,6 +42,20 @@ static void nested_svm_clear_insn_bytes(struct vmcb *vmcb)
 	       sizeof(vmcb->control.insn_bytes));
 }
 
+static void nested_svm_copy_insn_bytes(struct vmcb *to,
+				       const struct vmcb *from)
+{
+	u8 insn_len = from->control.insn_len;
+
+	nested_svm_clear_insn_bytes(to);
+
+	if (WARN_ON_ONCE(insn_len > sizeof(from->control.insn_bytes)))
+		return;
+
+	to->control.insn_len = insn_len;
+	memcpy(to->control.insn_bytes, from->control.insn_bytes, insn_len);
+}
+
 static bool nested_svm_vmexit_has_insn_bytes(const struct vmcb *vmcb)
 {
 	u64 exit_code = vmcb->control.exit_code;
@@ -67,6 +81,25 @@ static void nested_svm_clear_vmcb02_insn_bytes(struct vcpu_svm *svm)
 	svm->nested.vmcb02_insn_bytes_fresh = false;
 }
 
+static void nested_svm_update_vmcb12_insn_bytes(struct kvm_vcpu *vcpu,
+						struct vmcb *vmcb12,
+						const struct vmcb *vmcb02)
+{
+	struct vcpu_svm *svm = to_svm(vcpu);
+
+	nested_svm_clear_insn_bytes(vmcb12);
+
+	if (!guest_cpu_cap_has(vcpu, X86_FEATURE_DECODEASSISTS) ||
+	    !nested_svm_vmexit_has_insn_bytes(vmcb02))
+		goto out;
+
+	if (svm->nested.vmcb02_insn_bytes_fresh)
+		nested_svm_copy_insn_bytes(vmcb12, vmcb02);
+
+out:
+	svm->nested.vmcb02_insn_bytes_fresh = false;
+}
+
 static void nested_svm_inject_npf_exit(struct kvm_vcpu *vcpu,
 				       struct x86_exception *fault,
 				       bool from_hardware)
@@ -1332,6 +1365,8 @@ static int nested_svm_vmexit_update_vmcb12(struct kvm_vcpu *vcpu)
 	if (guest_cpu_cap_has(vcpu, X86_FEATURE_NRIPS))
 		vmcb12->control.next_rip  = vmcb02->control.next_rip;
 
+	nested_svm_update_vmcb12_insn_bytes(vcpu, vmcb12, vmcb02);
+
 	if (nested_vmcb12_has_lbrv(vcpu))
 		svm_copy_lbrs(&vmcb12->save, &vmcb02->save);
 
-- 
2.43.7