[MODERATED] Re: [PATCH 1/2] v3 more sampling fun 1

On Thu, Mar 12, 2020 at 08:25:01AM -0700, speck for Luck, Tony wrote:
> On Thu, Mar 12, 2020 at 01:34:50AM +0000, speck for Andrew Cooper wrote:
> > Particularly with this issue where it seems that no hypervisor is
> > interested in offering the knob to guest kernels (so could at least
> > infer based on SRBDS_CTRL), nor is there an ARCH_CAPS_$FOO_NO bit which
> > could be filled in by a hypervisor on unaffected or mitigated hardware.
> 
> Maybe that is the solution?  We allocated a s/w (VMM) bit in
> ARCH_CAPABILITIES for the TLB DoS issue for the nested hypervisor case.
> Should we do that again for this issue?

Bah, memory fail. I was actually thinking of bit 3 SKIP_L1DFL_VMENTRY
that told a nested VMM it didn't need to flush L1D again for L1TF as
an outer VMM was already handling that.

> If you think so, then we can take this discussion to Keybase so
> that the other VMM vendors who hang out there can chime in.
> 
> [Note that it isn't my call to allocate a bit in ARCH_CAPABILITIES,
> but I can campaign for it if folks want it].
> 
> -Tony