KVM: nVMX: Rename nested.vmcs01_* fields to nested.pre_vmenter_*

Rename the fields in struct nested_vmx used to snapshot pre-VM-Enter
values to reflect that they can hold L2's values when restoring nested
state, e.g. if userspace restores MSRs before nested state.  As crazy as
it seems, restoring MSRs before nested state actually works (because KVM
goes out if it's way to make it work), even though the initial MSR writes
will hit vmcs01 despite holding L2 values.

Add a related comment to vmx_enter_smm() to call out that using the
common VM-Exit and VM-Enter helpers to emulate SMI and RSM is wrong and
broken.  The few MSRs that have snapshots _could_ be fixed by taking a
snapshot prior to the forced VM-Exit instead of at forced VM-Enter, but
that's just the tip of the iceberg as the rather long list of MSRs that
aren't snapshotted (hello, VM-Exit MSR load list) can't be handled this
way.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20220614215831.3762138-4-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 7 insertions, 0 deletions

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 61962f3c4b28..b4d3820e9800 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -7847,6 +7847,13 @@ static int vmx_enter_smm(struct kvm_vcpu *vcpu, char *smstate)
 {
 	struct vcpu_vmx *vmx = to_vmx(vcpu);
 
+	/*
+	 * TODO: Implement custom flows for forcing the vCPU out/in of L2 on
+	 * SMI and RSM.  Using the common VM-Exit + VM-Enter routines is wrong
+	 * SMI and RSM only modify state that is saved and restored via SMRAM.
+	 * E.g. most MSRs are left untouched, but many are modified by VM-Exit
+	 * and VM-Enter, and thus L2's values may be corrupted on SMI+RSM.
+	 */
 	vmx->nested.smm.guest_mode = is_guest_mode(vcpu);
 	if (vmx->nested.smm.guest_mode)
 		nested_vmx_vmexit(vcpu, -1, 0, 0);