KVM: nVMX: Stuff vmcs02.TSC_MULTIPLIER early on for nested early checks

If KVM is doing "early" nested VM-Enter consistency checks and TSC scaling
is supported, stuff vmcs02's TSC Multiplier early on to avoid getting a
false positive VM-Fail due to trying to do VM-Enter with TSC_MULTIPLIER=0.
To minimize complexity around L1 vs. L2 TSC, KVM sets the actual TSC
Multiplier rather late during VM-Entry, i.e. may have '0' at the time of
early consistency checks.

If vmcs12 has TSC Scaling enabled, use the multiplier from vmcs12 so that
nested early checks actually check vmcs12 state, otherwise throw in an
arbitrary value of '1' (anything non-zero is legal).

Fixes: d041b5ea9335 ("KVM: nVMX: Enable nested TSC scaling")
Link: https://lore.kernel.org/r/20250919005955.1366256-8-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index 77b5f75cc2bb5f7afc334e4c2f8f87072f72f0b8..efca276c67f0908e7bdaa4721d3fbdccf7118be0 100644 (file)
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -2371,6 +2371,13 @@ static void prepare_vmcs02_early_rare(struct vcpu_vmx *vmx,
                else
                        vmcs_write16(VIRTUAL_PROCESSOR_ID, vmx->vpid);
        }
+
+       if (kvm_caps.has_tsc_control && nested_early_check) {
+               if (nested_cpu_has2(vmcs12, SECONDARY_EXEC_TSC_SCALING))
+                       vmcs_write64(TSC_MULTIPLIER, vmcs12->tsc_multiplier);
+               else
+                       vmcs_write64(TSC_MULTIPLIER, 1);
+       }
 }
 
 static void prepare_vmcs02_early(struct vcpu_vmx *vmx, struct loaded_vmcs *vmcs01,