Messages in this thread | | | Date | Fri, 15 Sep 2023 07:27:27 +0200 | Subject | Re: [PATCH v10 08/38] x86/cpufeatures: Add the cpu feature bit for FRED | From | Juergen Gross <> |
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On 15.09.23 03:07, Thomas Gleixner wrote: > On Thu, Sep 14 2023 at 14:15, andrew wrote: >> PV guests are never going to see FRED (or LKGS for that matter) because >> it advertises too much stuff which simply traps because the kernel is in >> CPL3. >> >> That said, the 64bit PV ABI is a whole lot closer to FRED than it is to >> IDT delivery. (Almost as if we decided 15 years ago that giving the PV >> guest kernel a good stack and GSbase was the right thing to do...) > > No argument about that. > >> In some copious free time, I think we ought to provide a >> minorly-paravirt FRED to PV guests because there are still some >> improvements available as low hanging fruit. >> >> My plan was to have a PV hypervisor leaf advertising paravirt versions >> of hardware features, so a guest could see "I don't have architectural >> FRED, but I do have paravirt-FRED which is as similar as we can >> reasonably make it". The same goes for a whole bunch of other features. > > *GROAN* > > I told you before that we want less paravirt nonsense and not more.
I agree.
We will still have to support the PV stuff for non-FRED hypervisors even with pv-FRED being available on new Xen. So adding pv-FRED would just add more PV interfaces without the ability to remove old stuff.
Juergen
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