[PATCH pve-qemu] parse-cpu-flags: stop filtering out 'pmu'

[PATCH pve-qemu] parse-cpu-flags: stop filtering out 'pmu'

[Arthur Bied-Charreton]

'pmu' was excluded from the list of flags in the custom CPU flag dialog
because it is not a CPUID flag (not part of '-cpu help' output).
However, it is a plain boolean property so it fits the [+-]<flag> syntax
from the custom CPU config, and QEMU accepts it when set manually via
'+pmu'.

Windows guests using VBS need a virtual PMU, which is not enabled by
default on many models (EPYC-Turin, EPYC-Genoa, SapphireRapids, and
presumably others I have not tested). This currently requires users to
edit the config by hand since the flag cannot be selected in the UI.

Remove 'pmu' from the blacklist so it shows up in the generated flag
list.

Reported-by: David Riley <d.riley@proxmox.com>
Signed-off-by: Arthur Bied-Charreton <a.bied-charreton@proxmox.com>
---
 debian/parse-cpu-flags.pl | 1 -
 1 file changed, 1 deletion(-)

diff --git a/debian/parse-cpu-flags.pl b/debian/parse-cpu-flags.pl
index e680f99..e1af0e8 100755
--- a/debian/parse-cpu-flags.pl
+++ b/debian/parse-cpu-flags.pl
@@ -66,7 +66,6 @@ my $filtered_props = {
         'legacy-multi-node' => 1,
         lmce => 1,
         migratable => 1,
-        pmu => 1,
         realized => 1,
         'start-powered-off' => 1,
         'tcg-cpuid' => 1,
-- 
2.47.3

Re: [PATCH pve-qemu] parse-cpu-flags: stop filtering out 'pmu'

[Fiona Ebner]

Am 13.10.26 um 10:32 AM schrieb Arthur Bied-Charreton:
> 'pmu' was excluded from the list of flags in the custom CPU flag dialog
> because it is not a CPUID flag (not part of '-cpu help' output).
> However, it is a plain boolean property so it fits the [+-]<flag> syntax
> from the custom CPU config, and QEMU accepts it when set manually via
> '+pmu'.

What I wanted to write: if it's not a CPUID flag, wouldn't it be better
to expose it as a separate property? I.e. add to the $cpu_fmt schema and
have a separate checkbox in the UI?

But then I looked into the implementation and the 'pmu' property is very
closely related to the CPUID_EXT_PDCM flag, so it makes a lot of sense
if it goes through the same "on which nodes is it supported" checks and
if we treat it as a flag.

Could you adapt the commit message to reflect this? IMHO the argument
with QEMU accepting the same syntax is rather weak. There has to be
conceptual similarity too, which there is :)

> 
> Windows guests using VBS need a virtual PMU, which is not enabled by
> default on many models (EPYC-Turin, EPYC-Genoa, SapphireRapids, and
> presumably others I have not tested). This currently requires users to
> edit the config by hand since the flag cannot be selected in the UI.
> 
> Remove 'pmu' from the blacklist so it shows up in the generated flag
> list.
> 
> Reported-by: David Riley <d.riley@proxmox.com>
> Signed-off-by: Arthur Bied-Charreton <a.bied-charreton@proxmox.com>
> ---
>  debian/parse-cpu-flags.pl | 1 -
>  1 file changed, 1 deletion(-)
> 
> diff --git a/debian/parse-cpu-flags.pl b/debian/parse-cpu-flags.pl
> index e680f99..e1af0e8 100755
> --- a/debian/parse-cpu-flags.pl
> +++ b/debian/parse-cpu-flags.pl
> @@ -66,7 +66,6 @@ my $filtered_props = {
>          'legacy-multi-node' => 1,
>          lmce => 1,
>          migratable => 1,
> -        pmu => 1,
>          realized => 1,
>          'start-powered-off' => 1,
>          'tcg-cpuid' => 1,

Note: you also need to add it to debian/recognized-CPUID-flags-x86_64

Re: [PATCH pve-qemu] parse-cpu-flags: stop filtering out 'pmu'

[Arthur Bied-Charreton]

On Tue, Oct 13, 2026 at 11:19:11AM +0200, Fiona Ebner wrote:
> Am 13.10.26 um 10:32 AM schrieb Arthur Bied-Charreton:
> > 'pmu' was excluded from the list of flags in the custom CPU flag dialog
> > because it is not a CPUID flag (not part of '-cpu help' output).
> > However, it is a plain boolean property so it fits the [+-]<flag> syntax
> > from the custom CPU config, and QEMU accepts it when set manually via
> > '+pmu'.
> 
> What I wanted to write: if it's not a CPUID flag, wouldn't it be better
> to expose it as a separate property? I.e. add to the $cpu_fmt schema and
> have a separate checkbox in the UI?
> 
> But then I looked into the implementation and the 'pmu' property is very
> closely related to the CPUID_EXT_PDCM flag, so it makes a lot of sense
> if it goes through the same "on which nodes is it supported" checks and
> if we treat it as a flag.
> 
> Could you adapt the commit message to reflect this? IMHO the argument
> with QEMU accepting the same syntax is rather weak. There has to be
> conceptual similarity too, which there is :)
> 
fair enough, will adapt the message. thanks for looking into it!
> > 
> > Windows guests using VBS need a virtual PMU, which is not enabled by
> > default on many models (EPYC-Turin, EPYC-Genoa, SapphireRapids, and
> > presumably others I have not tested). This currently requires users to
> > edit the config by hand since the flag cannot be selected in the UI.
> > 
> > Remove 'pmu' from the blacklist so it shows up in the generated flag
> > list.
> > 
> > Reported-by: David Riley <d.riley@proxmox.com>
> > Signed-off-by: Arthur Bied-Charreton <a.bied-charreton@proxmox.com>
> > ---
> >  debian/parse-cpu-flags.pl | 1 -
> >  1 file changed, 1 deletion(-)
> > 
> > diff --git a/debian/parse-cpu-flags.pl b/debian/parse-cpu-flags.pl
> > index e680f99..e1af0e8 100755
> > --- a/debian/parse-cpu-flags.pl
> > +++ b/debian/parse-cpu-flags.pl
> > @@ -66,7 +66,6 @@ my $filtered_props = {
> >          'legacy-multi-node' => 1,
> >          lmce => 1,
> >          migratable => 1,
> > -        pmu => 1,
> >          realized => 1,
> >          'start-powered-off' => 1,
> >          'tcg-cpuid' => 1,
> 
> Note: you also need to add it to debian/recognized-CPUID-flags-x86_64
I somehow completely forgot, thanks for noticing :)

superseded: [PATCH pve-qemu] parse-cpu-flags: stop filtering out 'pmu'

[Arthur Bied-Charreton]

superseded by:
https://lore.proxmox.com/pve-devel/20261013095241.410553-1-a.bied-charreton@proxmox.com/T/#u