[PATCH v7 3/8] KVM: nSVM: Track valid hardware DecodeAssist bytes

[Tina Zhang]

VMCB02 instruction bytes are valid only for the hardware VM-Exit that
populated them.  Track whether VMCB02 contains instruction bytes for the
data #PF or #NPF currently being reflected to L1 so that stale bytes are
not copied to VMCB12.

Invalidate VMCB02's instruction-byte state when preparing VMCB02,
normally in response to an emulated VMRUN.  Mark the bytes as valid only
when the current VMCB02 exit is a data #PF or #NPF.  Opcode exits and
instruction-fetch faults are excluded by inspecting the exit state.

A subsequent change will use this state when propagating hardware
DecodeAssist instruction bytes to VMCB12.

Signed-off-by: Tina Zhang <zhang_wei@xxxxxxxxxxxxxx>
---
 arch/x86/kvm/svm/nested.c | 38 +++++++++++++++++++++++++++++++++++++-
 arch/x86/kvm/svm/svm.h    |  3 +++
 2 files changed, 40 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index 23d29597d6bf..378467288716 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -35,6 +35,35 @@
 
 #define CC KVM_NESTED_VMENTER_CONSISTENCY_CHECK
 
+static void nested_svm_invalidate_insn_bytes(struct vmcb *vmcb)
+{
+	vmcb->control.insn_len = 0;
+}
+
+static bool nested_svm_vmexit_supports_insn_bytes(const struct vmcb *vmcb)
+{
+	u64 exit_code = vmcb->control.exit_code;
+
+	if (exit_code != SVM_EXIT_NPF &&
+	    exit_code != SVM_EXIT_EXCP_BASE + PF_VECTOR)
+		return false;
+
+	return !(vmcb->control.exit_info_1 & PFERR_FETCH_MASK);
+}
+
+static void nested_svm_set_vmcb02_insn_bytes_valid(struct vcpu_svm *svm)
+{
+	svm->nested.vmcb02_insn_bytes_valid =
+		cpu_feature_enabled(X86_FEATURE_DECODEASSISTS) &&
+		nested_svm_vmexit_supports_insn_bytes(svm->nested.vmcb02.ptr);
+}
+
+static void nested_svm_invalidate_vmcb02_insn_bytes(struct vcpu_svm *svm)
+{
+	nested_svm_invalidate_insn_bytes(svm->nested.vmcb02.ptr);
+	svm->nested.vmcb02_insn_bytes_valid = false;
+}
+
 static void nested_svm_inject_npf_exit(struct kvm_vcpu *vcpu,
 				       struct x86_exception *fault,
 				       bool from_hardware)
@@ -68,6 +97,10 @@ static void nested_svm_inject_npf_exit(struct kvm_vcpu *vcpu,
 				    (fault->error_code & ~PFERR_GUEST_FAULT_STAGE_MASK);
 	vmcb->control.exit_info_2 = fault->address;
 
+	if (from_hardware)
+		nested_svm_set_vmcb02_insn_bytes_valid(svm);
+	else
+		nested_svm_invalidate_vmcb02_insn_bytes(svm);
 	nested_svm_vmexit(svm);
 }
 
@@ -873,6 +906,7 @@ static void nested_vmcb02_prepare_control(struct vcpu_svm *svm)
 	 * Filled at exit: exit_code, exit_info_1, exit_info_2, exit_int_info,
 	 * exit_int_info_err, next_rip, insn_len, insn_bytes.
 	 */
+	nested_svm_invalidate_vmcb02_insn_bytes(svm);
 
 	if (guest_cpu_cap_has(vcpu, X86_FEATURE_VGIF) &&
 	    (vmcb12_ctrl->int_ctl & V_GIF_ENABLE_MASK))
@@ -1653,8 +1687,10 @@ int nested_svm_exit_handled(struct vcpu_svm *svm)
 
 	vmexit = nested_svm_intercept(svm);
 
-	if (vmexit == NESTED_EXIT_DONE)
+	if (vmexit == NESTED_EXIT_DONE) {
+		nested_svm_set_vmcb02_insn_bytes_valid(svm);
 		nested_svm_vmexit(svm);
+	}
 
 	return vmexit;
 }
diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
index e958943b8162..1e12ef1105c0 100644
--- a/arch/x86/kvm/svm/svm.h
+++ b/arch/x86/kvm/svm/svm.h
@@ -243,6 +243,9 @@ struct svm_nested_state {
 	 * on its side.
 	 */
 	bool force_msr_bitmap_recalc;
+
+	/* True if VMCB02 has instruction bytes for the current nested exit. */
+	bool vmcb02_insn_bytes_valid;
 };
 
 struct vcpu_sev_es_state {
-- 
2.43.7