On Thu, Feb 05, 2026, Jim Mattson wrote: > When nested NPT is enabled and KVM_SET_NESTED_STATE is used to restore an > old checkpoint (without a valid gPAT), the current IA32_PAT value must be > used as L2's gPAT. > > The current IA32_PAT value may be restored by KVM_SET_MSRS after > KVM_SET_NESTED_STATE. Furthermore, there may be a KVM_GET_NESTED_STATE > before the first KVM_RUN. > > Introduce a new boolean, svm->nested.legacy_gpat_semantics. When set, hPAT > updates are also applied to gPAT, preserving the old behavior where L2 > shared L1's PAT. svm_vcpu_pre_run() clears this boolean at the first > KVM_RUN.
State this last point as a command and explain why. E.g. I think this is why? Clear legacy_gpat_semantics on KVM_RUN so that the legacy semantics are scoped to a single restore (inasmuch as possible). E.g. to support restoring a snapshot from an old KVM, and then later restoring a snapshot from a new KVM.
