Re: [PATCH v3 23/27] KVM: nSVM: Do not reset TLB_CONTROL in vmcb02 on nested VM-Enter

[Yosry Ahmed]

On Thu, Oct 15, 2026 at 4:16 PM Jim Mattson <jmattson@xxxxxxxxxx> wrote:
>
> On Mon, Oct 12, 2026 at 4:36 PM Yosry Ahmed <yosry@xxxxxxxxxx> wrote:
> >
> > Stop clearing TLB_CONTROL when preparing the control area of vmcb02, as
> > this potentially undoes pending TLB flushes for L2 (e.g. through
> > KVM_REQ_TLB_FLUSH while L1 is running), and remove the associated TODO
> > comment.
> >
> > This is currently harmless, because nested_svm_entry_tlb_flush() always
> > requests KVM_REQ_TLB_FLUSH_CURRENT on nested VM-Enter, which sets
> > TLB_CONTROL again before L2 is actually run. However, always flushing
> > will soon go away with proper TLB handling for L2, at which point always
> > clearing TLB_CONTROL would be a bug.
> >
> > Clearing TLB_CONTROL on nested VM-Enter was probably done because
> > TLB_CONTROL is not cleared by the CPU on VM-Exit. However, KVM always
> > clears TLB_CONTROL in the active VMCB after a successful VMRUN. Hence,
> > at nested VM-Enter, TLB_CONTROL in vmcb02 can only be non-zero if a TLB
> > flush is queued for L2 while L1 is running (i.e. KVM_REQ_TLB_FLUSH), and
>
> Nit: s/i.e./e.g./

Ack.

>
> > that should never be ignored.
> >
> > Signed-off-by: Yosry Ahmed <yosry@xxxxxxxxxx>
> Reviewed-by: Jim Mattson <jmattson@xxxxxxxxxx>