ppc64le kunit test failure: guest_state_buffer_test

FYI, the KUnit test arch/powerpc/kvm/test-guest-state-buffer.c is failing when run in QEMU PPC64LE:

[  146.554299][    T1]     KTAP version 1^M
[  146.554348][    T1]     # Subtest: guest_state_buffer_test^M
[  146.554543][    T1]     # module: test_guest_state_buffer^M
[  146.554927][    T1]     1..7^M
[  146.556873][    T1]     ok 1 test_creating_buffer^M
[  146.558221][    T1]     ok 2 test_adding_element^M
[  146.559532][    T1]     ok 3 test_gs_bitmap^M
[  146.560309][    T1]     ok 4 test_gs_parsing^M
[  146.561246][    T1]     ok 5 test_gs_msg^M
[  146.562116][    T1]     ok 6 test_gs_hostwide_msg^M
[  146.562911][  T428]     # test_gs_hostwide_counters: ASSERTION FAILED at arch/powerpc/kvm/test-guest-state-buffer.c:488^M
[  146.562911][  T428]     Expected rc == 0, but^M
[  146.562911][  T428]         rc == -2 (0xfffffffffffffffe)^M
[  146.563600][    T1]     not ok 7 test_gs_hostwide_counters^M
[  146.563653][    T1] # guest_state_buffer_test: pass:6 fail:1 skip:0 total:7^M

Tested on next-20260602. I haven't bisected it.

Note that this test is in the defconfig.

- Eric

Hi Eric,

Thanks for trying and reporting this. This kunit test depends on availablility of Qemu commit 5f7d861e("spapr: nested: Add support for reporting Hostwide state counter ") [1] that was merged in v10.0.0.

Since you havent mentioned the qemu version used I assume its a version < v10.0.0 . With the qemu patch available you should see this test passing with results similar to as originally described in original cover letter of the patch series at [2] that introduced this kunit test.

[1] https://gitlab.com/qemu-project/qemu/-/commit/5f7d861e65d90e0446b8f22a0bc859a5d8058ea6

[2] https://lore.kernel.org/all/[email protected]/

Cheers
~ Vaibhav

Nope, it fails even on the master branch of QEMU.

- Eric

Hi Eric,

I just successfully tested this kunit test on kernel tag next-20260602 and qemu master HEAD == 405c32d2b18a("Merge tag 'pull-tpm-2026-06-01-1' of https://github.com/stefanberger/qemu-tpm into staging") [1]

If you are using Qemu >= v10.0.0 then the kunit test failure you reported is due to Qemu not enabling 'cap-nested-papr' capability which is needed to enable KVM-HV Apiv2 support in Qemu.

Without 'cap-nested-papr' Qemu doesnt register the H_GUEST_GET_STATE Hcall which this kunit test relies on. Hence it returns -2 (H_FUNCTION) for this unsupported HCall. The failure of kunit 'test_gs_hostwide_msg' is expected as the underlying hypervisor doesnt have support nested-papr APIv2 capability.

To fix this please enable qemu-system-ppc64 machine's capability cap-nested-papr to enable nested-papr APIv2 support.

Below is the test log showing successful 'guest_state_buffer_test' kunit test passing :

$ ./qemu-system-ppc64 --version
QEMU emulator version 11.0.50 (v11.0.0-1621-g405c32d2b1)
Copyright (c) 2003-2026 Fabrice Bellard and the QEMU Project developers

# kunit test is specific to nested-papr APIv2 so qemu cap-nested-papr needs to be enabled
$ ./qemu-system-ppc64 -display none -nographic -kernel ~/linux/vmlinux
-machine pseries,cap-nested-papr=true

<snip>
Booting from memory...
OF stdout device is: /vdevice/vty@71000000
Preparing to boot Linux version 7.1.0-rc6-next-20260602 (vaibhav@*********) (gcc (GCC) 16.1.1 20260515 (Red Hat 16.1.1-2), GNU ld version 2.46-3.fc44) #2 SMP PREEMPT Wed Jun 3 04:11:38 CDT 2026 Detected machine type: 0000000000000101

<snip>

[    4.335850][    T1]     KTAP version 1
[    4.335896][    T1]     # Subtest: guest_state_buffer_test
[    4.335946][    T1]     # module: test_guest_state_buffer
[    4.335970][    T1]     1..7
[    4.337296][    T1]     ok 1 test_creating_buffer
[    4.338998][    T1]     ok 2 test_adding_element
[    4.341996][    T1]     ok 3 test_gs_bitmap
[    4.343406][    T1]     ok 4 test_gs_parsing
[    4.345607][    T1]     ok 5 test_gs_msg
[    4.347247][    T1]     ok 6 test_gs_hostwide_msg
[    4.348012][  T131]     # test_gs_hostwide_counters: Guest Heap Size=0 bytes
[    4.348183][  T131]     # test_gs_hostwide_counters: Guest Heap Size Max=0 bytes
[    4.348350][  T131]     # test_gs_hostwide_counters: Guest Page-table Size=0 bytes
[    4.348653][  T131]     # test_gs_hostwide_counters: Guest Page-table Size Max=0 bytes
[    4.348813][  T131]     # test_gs_hostwide_counters: Guest Page-table Reclaim Size=0 bytes
[    4.349354][    T1]     ok 7 test_gs_hostwide_counters
[    4.349569][    T1] # guest_state_buffer_test: pass:7 fail:0 skip:0 total:7
[    4.349635][    T1] # Totals: pass:7 fail:0 skip:0 total:7
[    4.349708][    T1] ok 4 guest_state_buffer_test

Can you try adding 'cap-nested-papr=true' to the Qemu machine you are using and see if the problem resolves for you. If it persists can you please share the Qemu command line you are using.

[1] https://gitlab.com/qemu-project/qemu/-/commit/405c32d2b18a683ba36301351af75125d9afda08

Cheers
~ Vaibhav