[PATCH v2 4/4] KVM: SVM: Support #GP handling for the case of nested on nested

[Wei Huang]

Under the case of nested on nested (e.g. L0->L1->L2->L3), #GP triggered
by SVM instructions can be hided from L1. Instead the hypervisor can
inject the proper #VMEXIT to inform L1 of what is happening. Thus L1
can avoid invoking the #GP workaround. For this reason we turns on
guest VM's X86_FEATURE_SVME_ADDR_CHK bit for KVM running inside VM to
receive the notification and change behavior.

Co-developed-by: Bandan Das <b...@redhat.com>
Signed-off-by: Bandan Das <b...@redhat.com>
Signed-off-by: Wei Huang <wei.hua...@amd.com>
---
 arch/x86/kvm/svm/svm.c | 19 ++++++++++++++++++-
 1 file changed, 18 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 2a12870ac71a..89512c0e7663 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -2196,6 +2196,11 @@ static int svm_instr_opcode(struct kvm_vcpu *vcpu)
 
 static int emulate_svm_instr(struct kvm_vcpu *vcpu, int opcode)
 {
+       const int guest_mode_exit_codes[] = {
+               [SVM_INSTR_VMRUN] = SVM_EXIT_VMRUN,
+               [SVM_INSTR_VMLOAD] = SVM_EXIT_VMLOAD,
+               [SVM_INSTR_VMSAVE] = SVM_EXIT_VMSAVE,
+       };
        int (*const svm_instr_handlers[])(struct vcpu_svm *svm) = {
                [SVM_INSTR_VMRUN] = vmrun_interception,
                [SVM_INSTR_VMLOAD] = vmload_interception,
@@ -2203,7 +2208,14 @@ static int emulate_svm_instr(struct kvm_vcpu *vcpu, int 
opcode)
        };
        struct vcpu_svm *svm = to_svm(vcpu);
 
-       return svm_instr_handlers[opcode](svm);
+       if (is_guest_mode(vcpu)) {
+               svm->vmcb->control.exit_code = guest_mode_exit_codes[opcode];
+               svm->vmcb->control.exit_info_1 = 0;
+               svm->vmcb->control.exit_info_2 = 0;
+
+               return nested_svm_vmexit(svm);
+       } else
+               return svm_instr_handlers[opcode](svm);
 }
 
 /*
@@ -4034,6 +4046,11 @@ static void svm_vcpu_after_set_cpuid(struct kvm_vcpu 
*vcpu)
        /* Check again if INVPCID interception if required */
        svm_check_invpcid(svm);
 
+       if (nested && guest_cpuid_has(vcpu, X86_FEATURE_SVM)) {
+               best = kvm_find_cpuid_entry(vcpu, 0x8000000A, 0);
+               best->edx |= (1 << 28);
+       }
+
        /* For sev guests, the memory encryption bit is not reserved in CR3.  */
        if (sev_guest(vcpu->kvm)) {
                best = kvm_find_cpuid_entry(vcpu, 0x8000001F, 0);
-- 
2.27.0