[PATCH 1/7] KVM: nVMX: Introduce nested_evmcs_is_used()

Vitaly Kuznetsov
2021-05-11T11:20:18Z

Unlike regular set_current_vmptr(), nested_vmx_handle_enlightened_vmptrld()
can not be called directly from vmx_set_nested_state() as KVM may not have
all the information yet (e.g. HV_X64_MSR_VP_ASSIST_PAGE MSR may not be
restored yet). Enlightened VMCS is mapped later while getting nested state
pages. In the meantime, vmx->nested.hv_evmcs remains NULL and using it
for various checks is incorrect. In particular, if KVM_GET_NESTED_STATE is
called right after KVM_SET_NESTED_STATE, KVM_STATE_NESTED_EVMCS flag in the
resulting state will be unset (and such state will later fail to load).

Introduce nested_evmcs_is_used() and use 'is_guest_mode(vcpu) &&
vmx->nested.current_vmptr == -1ull' check to detect not-yet-mapped eVMCS
after restore.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
---
arch/x86/kvm/vmx/nested.c | 31 ++++++++++++++++++++++++++-----
1 file changed, 26 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index 6058a65a6ede..3080e00c8f90 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -141,6 +141,27 @@ static void init_vmcs_shadow_fields(void)
max_shadow_read_write_fields = j;
}

+static inline bool nested_evmcs_is_used(struct vcpu_vmx *vmx)
+{
+ struct kvm_vcpu *vcpu = &vmx->vcpu;
+
+ if (vmx->nested.hv_evmcs)
+ return true;
+
+ /*
+ * After KVM_SET_NESTED_STATE, enlightened VMCS is mapped during
+ * KVM_REQ_GET_NESTED_STATE_PAGES handling and until the request is
+ * processed vmx->nested.hv_evmcs is NULL. It is, however, possible to
+ * detect such state by checking 'nested.current_vmptr == -1ull' when
+ * vCPU is in guest mode, it is only possible with eVMCS.
+ */
+ if (unlikely(vmx->nested.enlightened_vmcs_enabled && is_guest_mode(vcpu) &&
+ (vmx->nested.current_vmptr == -1ull)))
+ return true;
+
+ return false;
+}
+
/*
* The following 3 functions, nested_vmx_succeed()/failValid()/failInvalid(),
* set the success or error code of an emulated VMX instruction (as specified
@@ -187,7 +208,7 @@ static int nested_vmx_fail(struct kvm_vcpu *vcpu, u32 vm_instruction_error)
* failValid writes the error number to the current VMCS, which
* can't be done if there isn't a current VMCS.
*/
- if (vmx->nested.current_vmptr == -1ull && !vmx->nested.hv_evmcs)
+ if (vmx->nested.current_vmptr == -1ull && !nested_evmcs_is_used(vmx))
return nested_vmx_failInvalid(vcpu);

return nested_vmx_failValid(vcpu, vm_instruction_error);
@@ -2208,7 +2229,7 @@ static void prepare_vmcs02_early(struct vcpu_vmx *vmx, struct vmcs12 *vmcs12)
u32 exec_control;
u64 guest_efer = nested_vmx_calc_efer(vmx, vmcs12);

- if (vmx->nested.dirty_vmcs12 || vmx->nested.hv_evmcs)
+ if (vmx->nested.dirty_vmcs12 || nested_evmcs_is_used(vmx))
prepare_vmcs02_early_rare(vmx, vmcs12);

/*
@@ -3437,7 +3458,7 @@ enum nvmx_vmentry_status nested_vmx_enter_non_root_mode(struct kvm_vcpu *vcpu,

load_vmcs12_host_state(vcpu, vmcs12);
vmcs12->vm_exit_reason = exit_reason.full;
- if (enable_shadow_vmcs || vmx->nested.hv_evmcs)
+ if (enable_shadow_vmcs || nested_evmcs_is_used(vmx))
vmx->nested.need_vmcs12_to_shadow_sync = true;
return NVMX_VMENTRY_VMEXIT;
}
@@ -4032,7 +4053,7 @@ static void sync_vmcs02_to_vmcs12(struct kvm_vcpu *vcpu, struct vmcs12 *vmcs12)
{
struct vcpu_vmx *vmx = to_vmx(vcpu);

- if (vmx->nested.hv_evmcs)
+ if (nested_evmcs_is_used(vmx))
sync_vmcs02_to_vmcs12_rare(vcpu, vmcs12);

vmx->nested.need_sync_vmcs02_to_vmcs12_rare = !vmx->nested.hv_evmcs;
@@ -6056,7 +6077,7 @@ static int vmx_get_nested_state(struct kvm_vcpu *vcpu,
if (vmx_has_valid_vmcs12(vcpu)) {
kvm_state.size += sizeof(user_vmx_nested_state->vmcs12);

- if (vmx->nested.hv_evmcs)
+ if (nested_evmcs_is_used(vmx))
kvm_state.flags |= KVM_STATE_NESTED_EVMCS;

if (is_guest_mode(vcpu) &&
--
2.30.2