Re: [PATCH v6 00/51] x86: Try to wrangle PV clocks vs. TSC

[Sean Christopherson <seanjc@xxxxxxxxxx>]

On Thu, Sep 10, 2026, David Woodhouse wrote:
> On Thu, 2026-09-10 at 10:59 -0700, Sean Christopherson wrote:
> > On Thu, Aug 06, 2026, Sean Christopherson wrote:
> > > The primary goal of this series to fix flaws with SNP and TDX guests 
> > > where a
> > > PV clock provided by the untrusted hypervisor is used instead of the 
> > > secure
> > > TSC that is controlled by trusted firmware.
> > > 
> > > The secondary goal is modernize running under KVM.  Currently, KVM guests 
> > > will
> > > use TSC for clocksource, but not sched_clock.  And Linux-as-a-KVM-guest 
> > > doesn't
> > > support paravirt enumeration of the TSC/APIC frequencies, even though QEMU
> > > provides that information by default.
> > > 
> > > The tertiary goal is to clean up the PV clock code to deduplicate logic 
> > > across
> > > hypervisors, and to hopefully make it all easier to maintain going 
> > > forward.
> > > 
> > > The quaternary goal is to clean up the TSC calibration code, which was 
> > > made
> > > stupidly hard to follow by hypervisor code mixing in with the native
> > > calibration routines, instead of being implemented as a pure alternative.
> > > 
> > > Note, the VMware and Xen changes still probably should get acks from those
> > > maintainers, as my understanding of what they're trying to do may be 
> > > flawed.
> > 
> > This (thankfully) still applies cleanly.  What can I do to help move this 
> > forward?
> 
> Nudge Thomas to spot that this is guest-side and we want him to pick it up, I 
> guess?

Amazingly, still applies cleanly on 7.4-rc1 and tip/master.  I know we're 
shortly
after the merge window, but this has been sitting idle for months and addresses
issues that are impacting a variety of end users.

Note, this also provides meaningful hardening for SNP and TDX.  /me stares 
intently
in the direction of Dave and Boris.