[PATCH v7 2/8] KVM: nSVM: Synthesize DecodeAssists EXITINFO for emulated intercepts

[Tina Zhang]

When the x86 emulator encounters an instruction intercepted by L1,
svm_check_intercept() synthesizes a nested VM-Exit without fresh hardware
DecodeAssist state.  Populate the architectural EXITINFO1 field when
DecodeAssists is exposed to L1.

Provide the GPR number for MOV CR/DR, the interrupt vector for INTn, and
the linear address for INVLPG.  Preserve the MOV-to-CR0 decode information
when a selective CR0 write intercept is triggered.  Leave EXITINFO1 clear
for CLTS, LMSW, SMSW, and INVLPGA; the INVLPGA address remains in guest
rAX.  Leave EXITINFO1 unchanged when DecodeAssists is not exposed, and
leave unrelated intercepts unchanged.

Signed-off-by: Tina Zhang <zhang_wei@xxxxxxxxxxxxxx>
---
 arch/x86/kvm/svm/svm.c | 27 +++++++++++++++++++++++++++
 1 file changed, 27 insertions(+)

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index f5aa3d7d3a10..e83e4e5e7b93 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -4837,6 +4837,7 @@ static int svm_check_intercept(struct kvm_vcpu *vcpu,
 	int vmexit, ret = X86EMUL_CONTINUE;
 	struct __x86_intercept icpt_info;
 	struct vmcb *vmcb = svm->vmcb;
+	bool decode_assists;
 
 	if (info->intercept >= ARRAY_SIZE(x86_intercept_map))
 		goto out;
@@ -4846,14 +4847,26 @@ static int svm_check_intercept(struct kvm_vcpu *vcpu,
 	if (stage != icpt_info.stage)
 		goto out;
 
+	decode_assists = guest_cpu_cap_has(vcpu, X86_FEATURE_DECODEASSISTS);
+
 	switch (icpt_info.exit_code) {
 	case SVM_EXIT_READ_CR0:
 		if (info->intercept == x86_intercept_cr_read)
 			icpt_info.exit_code += info->modrm_reg;
+
+		if (decode_assists)
+			vmcb->control.exit_info_1 =
+				info->intercept == x86_intercept_cr_read ?
+				CR_VALID | (info->modrm_rm & SVM_EXITINFO_REG_MASK) : 0;
 		break;
 	case SVM_EXIT_WRITE_CR0: {
 		unsigned long cr0, val;
 
+		if (decode_assists)
+			vmcb->control.exit_info_1 =
+				info->intercept == x86_intercept_cr_write ?
+				CR_VALID | (info->modrm_rm & SVM_EXITINFO_REG_MASK) : 0;
+
 		/*
 		 * Adjust the exit code accordingly if a CR other than CR0 is
 		 * being written, and skip straight to the common handling as
@@ -4898,6 +4911,20 @@ static int svm_check_intercept(struct kvm_vcpu *vcpu,
 	case SVM_EXIT_READ_DR0:
 	case SVM_EXIT_WRITE_DR0:
 		icpt_info.exit_code += info->modrm_reg;
+		if (decode_assists)
+			vmcb->control.exit_info_1 = info->modrm_rm & SVM_EXITINFO_REG_MASK;
+		break;
+	case SVM_EXIT_SWINT:
+		if (decode_assists)
+			vmcb->control.exit_info_1 = info->src_val & 0xff;
+		break;
+	case SVM_EXIT_INVLPG:
+		if (decode_assists)
+			vmcb->control.exit_info_1 = info->invlpg_linear_addr;
+		break;
+	case SVM_EXIT_INVLPGA:
+		if (decode_assists)
+			vmcb->control.exit_info_1 = 0;
 		break;
 	case SVM_EXIT_MSR:
 		if (info->intercept == x86_intercept_wrmsr)
-- 
2.43.7