[PATCH 2/2] nSVM: delay MSR permission processing to first nested VM run

From: Paolo Bonzini
Date: Mon Sep 28 2020 - 07:51:59 EST


Allow userspace to set up the memory map after KVM_SET_NESTED_STATE;
to do so, move the call to nested_svm_vmrun_msrpm inside the
KVM_REQ_GET_NESTED_STATE_PAGES handler (which is currently
not used by nSVM). This is similar to what VMX does already.

Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
---
arch/x86/kvm/svm/nested.c | 20 ++++++++++++++++++--
1 file changed, 18 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index 598a769f1961..ab7ff2701dec 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -200,6 +200,20 @@ static bool nested_svm_vmrun_msrpm(struct vcpu_svm *svm)
return true;
}

+static bool svm_get_nested_state_pages(struct kvm_vcpu *vcpu)
+{
+ struct vcpu_svm *svm = to_svm(vcpu);
+ if (!nested_svm_vmrun_msrpm(svm)) {
+ vcpu->run->exit_reason = KVM_EXIT_INTERNAL_ERROR;
+ vcpu->run->internal.suberror =
+ KVM_INTERNAL_ERROR_EMULATION;
+ vcpu->run->internal.ndata = 0;
+ return false;
+ }
+
+ return true;
+}
+
static bool nested_vmcb_check_controls(struct vmcb_control_area *control)
{
if ((control->intercept & (1ULL << INTERCEPT_VMRUN)) == 0)
@@ -702,6 +716,8 @@ void svm_leave_nested(struct vcpu_svm *svm)
copy_vmcb_control_area(&vmcb->control, &hsave->control);
nested_svm_uninit_mmu_context(&svm->vcpu);
}
+
+ kvm_clear_request(KVM_REQ_GET_NESTED_STATE_PAGES, &svm->vcpu);
}

static int nested_svm_exit_handled_msr(struct vcpu_svm *svm)
@@ -1147,8 +1163,7 @@ static int svm_set_nested_state(struct kvm_vcpu *vcpu,
load_nested_vmcb_control(svm, ctl);
nested_prepare_vmcb_control(svm);

- if (!nested_svm_vmrun_msrpm(svm))
- return -EINVAL;
+ kvm_make_request(KVM_REQ_GET_NESTED_STATE_PAGES, vcpu);

out_set_gif:
svm_set_gif(svm, !!(kvm_state->flags & KVM_STATE_NESTED_GIF_SET));
@@ -1163,6 +1178,7 @@ static int svm_set_nested_state(struct kvm_vcpu *vcpu,

struct kvm_x86_nested_ops svm_nested_ops = {
.check_events = svm_check_nested_events,
+ .get_nested_state_pages = svm_get_nested_state_pages,
.get_state = svm_get_nested_state,
.set_state = svm_set_nested_state,
};
--
2.26.2