REGRESSION on linux-next (next-20250919)

["Borah, Chaitanya Kumar" <chaitanya.kumar.borah@intel.com>]

Hello Sean,

Hope you are doing well. I am Chaitanya from the linux graphics team in 
Intel.

This mail is regarding a regression we are seeing in our CI runs[1] on
linux-next repository.

Since the version next-20250919 [2], we are seeing the following regression

`````````````````````````````````````````````````````````````````````````````````
<4>[   10.973827] ------------[ cut here ]------------
<4>[   10.973841] WARNING: arch/x86/events/core.c:3089 at 
perf_get_x86_pmu_capability+0xd/0xc0, CPU#15: (udev-worker)/386
...
<4>[   10.974028] Call Trace:
<4>[   10.974030]  <TASK>
<4>[   10.974033]  ? kvm_init_pmu_capability+0x2b/0x190 [kvm]
<4>[   10.974154]  kvm_x86_vendor_init+0x1b0/0x1a40 [kvm]
<4>[   10.974248]  vmx_init+0xdb/0x260 [kvm_intel]
<4>[   10.974278]  ? __pfx_vt_init+0x10/0x10 [kvm_intel]
<4>[   10.974296]  vt_init+0x12/0x9d0 [kvm_intel]
<4>[   10.974309]  ? __pfx_vt_init+0x10/0x10 [kvm_intel]
<4>[   10.974322]  do_one_initcall+0x60/0x3f0
<4>[   10.974335]  do_init_module+0x97/0x2b0
<4>[   10.974345]  load_module+0x2d08/0x2e30
<4>[   10.974349]  ? __kernel_read+0x158/0x2f0
<4>[   10.974370]  ? kernel_read_file+0x2b1/0x320
<4>[   10.974381]  init_module_from_file+0x96/0xe0
<4>[   10.974384]  ? init_module_from_file+0x96/0xe0
<4>[   10.974399]  idempotent_init_module+0x117/0x330
<4>[   10.974415]  __x64_sys_finit_module+0x73/0xe0
...
`````````````````````````````````````````````````````````````````````````````````
Details log can be found in [3].

After bisecting the tree, the following patch [4] seems to be the first 
"bad" commit

`````````````````````````````````````````````````````````````````````````````````````````````````````````
 From 51f34b1e650fc5843530266cea4341750bd1ae37 Mon Sep 17 00:00:00 2001

From: Sean Christopherson <seanjc@google.com>

Date: Wed, 6 Aug 2025 12:56:39 -0700

Subject: KVM: x86/pmu: Snapshot host (i.e. perf's) reported PMU capabilities

Take a snapshot of the unadulterated PMU capabilities provided by perf so
that KVM can compare guest vPMU capabilities against hardware capabilities
when determining whether or not to intercept PMU MSRs (and RDPMC).
`````````````````````````````````````````````````````````````````````````````````````````````````````````

We also verified that if we revert the patch the issue is not seen.

Could you please check why the patch causes this regression and provide 
a fix if necessary?

Thank you.

Regards

Chaitanya

[1]
https://intel-gfx-ci.01.org/tree/linux-next/combined-alt.html?
[2] 
https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/?h=next-20250919
[3]
https://intel-gfx-ci.01.org/tree/linux-next/next-20250919/bat-arlh-2/boot0.txt
[4] 
https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/?h=next-20250919&id=51f34b1e650fc5843530266cea4341750bd1ae37