[PATCH 1/8] KVM: nSVM: Sync next_rip field from vmcb12 to vmcb02

Sean Christopherson
2022-04-02T01:09:17Z

From: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>

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).

Signed-off-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>
Co-developed-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
arch/x86/kvm/svm/nested.c | 22 +++++++++++++++++++---
arch/x86/kvm/svm/svm.h | 1 +
2 files changed, 20 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index 73b545278f5f..9a6dc2b38fcf 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -369,6 +369,7 @@ 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;
@@ -606,7 +607,8 @@ 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;
@@ -660,6 +662,19 @@ 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)
@@ -743,7 +758,7 @@ 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,
@@ -1422,6 +1437,7 @@ 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;
@@ -1606,7 +1622,7 @@ 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, save->rip);

/*
* While the nested guest CR3 is already checked and set by
diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
index e246793cbeae..47e7427d0395 100644
--- a/arch/x86/kvm/svm/svm.h
+++ b/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;
--
2.35.1.1094.g7c7d902a7c-goog