Re: [PATCH v3 13/27] KVM: nSVM: Add a placeholder ASID for L2

[Jim Mattson]

On Mon, Oct 12, 2026 at 4:36 PM Yosry Ahmed <yosry@xxxxxxxxxx> wrote:
>
> In preparation for introducing a separate ASID for L2, introduce a
> 'placeholder' ASID that is still the same as L1's ASID. This will
> facilitate future changes that need to distinguish L1 and L2's ASIDs,
> before actually using a different ASID for L1 and L2.
>
> On SEV VM migration, copy the new SEV ASID into asid02 and vmcb02, in
> case nested was already initialized on the destination vCPU before
> migration.
>
> No functional change intended.
>
> Signed-off-by: Yosry Ahmed <yosry@xxxxxxxxxx>
> ---
>  arch/x86/kvm/svm/nested.c | 5 +++--
>  arch/x86/kvm/svm/sev.c    | 9 +++++++++
>  arch/x86/kvm/svm/svm.h    | 2 ++
>  3 files changed, 14 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
> index bfb297b7d71ab..780132725bb79 100644
> --- a/arch/x86/kvm/svm/nested.c
> +++ b/arch/x86/kvm/svm/nested.c
> @@ -701,7 +701,6 @@ static void nested_svm_transition_tlb_flush(struct kvm_vcpu *vcpu)
>          *  - Honor L1's request to flush an ASID on nested VMRUN
>          *  - Sync nested NPT MMU on VMRUN that flushes L2's ASID[*]
>          *  - Don't crush a pending TLB flush in vmcb02 on nested VMRUN
> -        *  - Flush L1's ASID on KVM_REQ_TLB_FLUSH_GUEST

Um...How does this patch either do this TODO or render it moot?

>          *
>          * [*] Unlike nested EPT, SVM's ASID management can invalidate nested
>          *     NPT guest-physical mappings on VMRUN.

[ ... ]

> +       /*
> +        * If nested is already initialized on the destination vCPU, also update
> +        * the nested ASID to match the new SEV ASID.
> +        */
> +       if (dst_svm->nested.vmcb02.ptr) {
> +               dst_svm->nested.asid02 = asid;
> +               dst_svm->nested.vmcb02.ptr->control.asid = asid;

+1 to Sashiko.