Re: [PATCH v4 5/7] x86/resctrl: Resolve PMT and TPMI symbols at runtime

[Luck, Tony]

On Tue, Apr 07, 2026 at 11:40:49AM -0700, Reinette Chatre wrote:
> Hi Tony,
> 
> On 4/7/26 11:13 AM, Luck, Tony wrote:
> ...
> > Adding a "resctrl" line to /etc/fstab attempts the mount at 39.667. Three
> > seconds too early. No PMT events are found, and code in this V4 version
> > of the patch series marks the system as AET_NOT_PRESENT and will never
> > look again :-(
> > 
> > I can drop the AET_NOT_PRESENT state so that a retry will succeed. I don't
> > see another fix other than to document this limitation.
> > 
> > Workarounds are:
> > 1) Change the CONFIG to build pmt_telemetry into the kernel (where we
> >    are today, but haven't heard from Linux distros like Red Hat, SUSE etc.
> >    on whether this is acceptable.)
> > 2) Delay mounting the resctrl file system.
> 
> As I mentioned in https://lore.kernel.org/lkml/e85cd466-2202-4b40-82ed-91e421d8e073@xxxxxxxxx/
> I find (2) to be a poor user interface since it (a) requires user space to
> somehow know that the system supports AET and then (b) either delay for some
> indeterminate time or repetitively (for some indeterminate count) remount resctrl
> to obtain needed features. 
> 
> Considering all the complications, could you please provide the motivation
> for this series? I should have checked for this first. The cover letter does not
> contain this information.

Reinette,

I'm concerned that AET will not be available in Linux distros. The beta for
Ubuntu 26.04 is available. I downloaded the iso and booted. It has the v7.0
kernel, so AET is in the source. But checking the config I see:

   ubuntu@ubuntu:/boot$ grep VSEC config-7.0.0-10-generic
   CONFIG_INTEL_VSEC=m
   ubuntu@ubuntu:/boot$ grep INTEL_PMT config-7.0.0-10-generic
   CONFIG_INTEL_PMT_CLASS=m
   CONFIG_INTEL_PMT_TELEMETRY=m
   CONFIG_INTEL_PMT_CRASHLOG=m
   CONFIG_INTEL_PMT_DISCOVERY=m
   ubuntu@ubuntu:/boot$ grep AET config-7.0.0-10-generic
   ubuntu@ubuntu:/boot$

The default for most distributions is to build as much as possible as
modules. So I expect to see the same when Fedora, Red Hat, SUSE.

Even our internal intel-next daily builds are configuring modules (I did
get them to switch the relevant modules to built-in for one release cycle.
But they feel they should match what is done in production systems, so
they have switched back.

-Tony