KVM: nSVM: Sync next_rip field from vmcb12 to vmcb02

The next_rip field of a VMCB is *not* an output-only field for a VMRUN.
This field value (instead of the saved guest RIP) in used by the CPU for
the return address pushed on stack when injecting a software interrupt or
INT3 or INTO exception.

Make sure this field gets synced from vmcb12 to vmcb02 when entering L2 or
loading a nested state and NRIPS is exposed to L1.  If NRIPS is supported
in hardware but not exposed to L1 (nrips=0 or hidden by userspace), stuff
vmcb02's next_rip from the new L2 RIP to emulate a !NRIPS CPU (which
saves RIP on the stack as-is).

Reviewed-by: Maxim Levitsky <[email protected]>
Co-developed-by: Sean Christopherson <[email protected]>
Signed-off-by: Sean Christopherson <[email protected]>
Signed-off-by: Maciej S. Szmigiero <[email protected]>
Message-Id: <c2e0a3d78db3ae30530f11d4e9254b452a89f42b.1651440202.git.maciej.szmigiero@oracle.com>
Signed-off-by: Paolo Bonzini <[email protected]>

arch/x86/kvm/svm/nested.c

@@ -371,6 +371,7 @@ void __nested_copy_vmcb_control_to_cache(struct kvm_vcpu *vcpu,
 	to->nested_ctl          = from->nested_ctl;
 	to->event_inj           = from->event_inj;
 	to->event_inj_err       = from->event_inj_err;
+	to->next_rip            = from->next_rip;
 	to->nested_cr3          = from->nested_cr3;
 	to->virt_ext            = from->virt_ext;
 	to->pause_filter_count  = from->pause_filter_count;
@@ -608,7 +609,8 @@ static void nested_vmcb02_prepare_save(struct vcpu_svm *svm, struct vmcb *vmcb12
 	}
 }
 
-static void nested_vmcb02_prepare_control(struct vcpu_svm *svm)
+static void nested_vmcb02_prepare_control(struct vcpu_svm *svm,
+					  unsigned long vmcb12_rip)
 {
 	u32 int_ctl_vmcb01_bits = V_INTR_MASKING_MASK;
 	u32 int_ctl_vmcb12_bits = V_TPR_MASK | V_IRQ_INJECTION_BITS_MASK;
@@ -662,6 +664,19 @@ static void nested_vmcb02_prepare_control(struct vcpu_svm *svm)
 	vmcb02->control.event_inj           = svm->nested.ctl.event_inj;
 	vmcb02->control.event_inj_err       = svm->nested.ctl.event_inj_err;
 
+	/*
+	 * next_rip is consumed on VMRUN as the return address pushed on the
+	 * stack for injected soft exceptions/interrupts.  If nrips is exposed
+	 * to L1, take it verbatim from vmcb12.  If nrips is supported in
+	 * hardware but not exposed to L1, stuff the actual L2 RIP to emulate
+	 * what a nrips=0 CPU would do (L1 is responsible for advancing RIP
+	 * prior to injecting the event).
+	 */
+	if (svm->nrips_enabled)
+		vmcb02->control.next_rip    = svm->nested.ctl.next_rip;
+	else if (boot_cpu_has(X86_FEATURE_NRIPS))
+		vmcb02->control.next_rip    = vmcb12_rip;
+
 	vmcb02->control.virt_ext            = vmcb01->control.virt_ext &
 					      LBR_CTL_ENABLE_MASK;
 	if (svm->lbrv_enabled)
@@ -745,7 +760,7 @@ int enter_svm_guest_mode(struct kvm_vcpu *vcpu, u64 vmcb12_gpa,
 	nested_svm_copy_common_state(svm->vmcb01.ptr, svm->nested.vmcb02.ptr);
 
 	svm_switch_vmcb(svm, &svm->nested.vmcb02);
-	nested_vmcb02_prepare_control(svm);
+	nested_vmcb02_prepare_control(svm, vmcb12->save.rip);
 	nested_vmcb02_prepare_save(svm, vmcb12);
 
 	ret = nested_svm_load_cr3(&svm->vcpu, svm->nested.save.cr3,
@@ -1418,6 +1433,7 @@ static void nested_copy_vmcb_cache_to_control(struct vmcb_control_area *dst,
 	dst->nested_ctl           = from->nested_ctl;
 	dst->event_inj            = from->event_inj;
 	dst->event_inj_err        = from->event_inj_err;
+	dst->next_rip             = from->next_rip;
 	dst->nested_cr3           = from->nested_cr3;
 	dst->virt_ext              = from->virt_ext;
 	dst->pause_filter_count   = from->pause_filter_count;
@@ -1602,7 +1618,7 @@ static int svm_set_nested_state(struct kvm_vcpu *vcpu,
 	nested_copy_vmcb_control_to_cache(svm, ctl);
 
 	svm_switch_vmcb(svm, &svm->nested.vmcb02);
-	nested_vmcb02_prepare_control(svm);
+	nested_vmcb02_prepare_control(svm, svm->vmcb->save.rip);
 
 	/*
 	 * While the nested guest CR3 is already checked and set by

arch/x86/kvm/svm/svm.h

@@ -139,6 +139,7 @@ struct vmcb_ctrl_area_cached {
 	u64 nested_ctl;
 	u32 event_inj;
 	u32 event_inj_err;
+	u64 next_rip;
 	u64 nested_cr3;
 	u64 virt_ext;
 	u32 clean;