Re: [PATCH v3 1/4] KVM: VMX: Flush CPU buffers as needed if L1D cache flush is skipped

Jim Mattson
2025-10-27T22:03:37Z

On Tue, Oct 21, 2025 at 6:20 PM Pawan Gupta
<pawan.kumar.gupta@linux.intel.com> wrote:
>
> ...
> Thinking more on this, the software sequence is only invoked when the
> system doesn't have the L1D flushing feature added by a microcode update.
> In such a case system is not expected to have a flushing VERW either, which
> was introduced after L1TF. Also, the admin needs to have a very good reason
> for not updating the microcode for 5+ years :-)

KVM started reporting MD_CLEAR to userspace in Linux v5.2, but it
didn't report L1D_FLUSH to userspace until Linux v6.4, so there are
plenty of virtual CPUs with a flushing VERW that don't have the L1D
flushing feature.