Re: [PATCH v5 3/3] Add support for RAPL MSRs in KVM/Qemu

[Anthony Harivel]

Hi Daniel,

Daniel P. Berrangé, Apr 18, 2024 at 18:42:

> > +    if (kvm_is_rapl_feat_enable(cs)) {
> > +        if (!IS_INTEL_CPU(env)) {
> > +            error_setg(errp, "RAPL feature can only be\
> > +                              enabled with Intel CPU models");
> > +                return false;
> > +        }
> > +    }
>
> I see a crash in kvm_is_rapl_feat_enable() from this caller,
> when I run with this kind of command line:
>
>  $ qemu-system-x86_64 \
>       -kernel /lib/modules/6.6.9-100.fc38.x86_64/vmlinuz \
>       -initrd tiny-initrd.img  -m 2000 -serial stdio -nodefaults \
>       -display none -accel kvm -append "console=ttyS0 quiet"
>
>
> #0  0x0000555555bc14b7 in kvm_is_rapl_feat_enable 
> (cs=cs@entry=0x555557b83470) at ../target/i386/kvm/kvm.c:2531
> #1  0x0000555555bc7534 in kvm_cpu_realizefn (cs=0x555557b83470, 
> errp=0x7fffffffd2a0) at ../target/i386/kvm/kvm-cpu.c:54
> #2  0x0000555555d2432a in accel_cpu_common_realize (cpu=0x555557b83470, 
> errp=0x7fffffffd2a0) at ../accel/accel-target.c:130
> #3  0x0000555555cdd955 in cpu_exec_realizefn (cpu=cpu@entry=0x555557b83470, 
> errp=errp@entry=0x7fffffffd2a0) at ../cpu-target.c:137
> #4  0x0000555555c14b89 in x86_cpu_realizefn (dev=0x555557b83470, 
> errp=0x7fffffffd310) at ../target/i386/cpu.c:7320
> #5  0x0000555555d58f4b in device_set_realized (obj=<optimized out>, 
> value=<optimized out>, errp=0x7fffffffd390) at ../hw/core/qdev.c:510
> #6  0x0000555555d5d78d in property_set_bool (obj=0x555557b83470, v=<optimized 
> out>, name=<optimized out>, opaque=0x5555578558e0, errp=0x7fffffffd390)
>     at ../qom/object.c:2358
> #7  0x0000555555d60b0b in object_property_set (obj=obj@entry=0x555557b83470, 
> name=name@entry=0x55555607c799 "realized", v=v@entry=0x555557b8ccb0, 
> errp=0x7fffffffd390, 
>     errp@entry=0x555556e210d8 <error_fatal>) at ../qom/object.c:1472
> #8  0x0000555555d6444f in object_property_set_qobject
>     (obj=obj@entry=0x555557b83470, name=name@entry=0x55555607c799 "realized", 
> value=value@entry=0x555557854800, errp=errp@entry=0x555556e210d8 
> <error_fatal>)
>     at ../qom/qom-qobject.c:28
> #9  0x0000555555d61174 in object_property_set_bool
>     (obj=0x555557b83470, name=name@entry=0x55555607c799 "realized", 
> value=value@entry=true, errp=errp@entry=0x555556e210d8 <error_fatal>) at 
> ../qom/object.c:1541
> #10 0x0000555555d59a3c in qdev_realize (dev=<optimized out>, 
> bus=bus@entry=0x0, errp=errp@entry=0x555556e210d8 <error_fatal>) at 
> ../hw/core/qdev.c:292
> #11 0x0000555555bd51e0 in x86_cpu_new (x86ms=<optimized out>, apic_id=0, 
> errp=0x555556e210d8 <error_fatal>) at ../hw/i386/x86.c:105
> #12 0x0000555555bd52ce in x86_cpus_init (x86ms=x86ms@entry=0x555557aaed30, 
> default_cpu_version=<optimized out>) at ../hw/i386/x86.c:156
> #13 0x0000555555bdc1a7 in pc_init1 (machine=0x555557aaed30, 
> pci_type=0x55555604aa61 "i440FX") at ../hw/i386/pc_piix.c:185
> #14 0x0000555555947a11 in machine_run_board_init (machine=0x555557aaed30, 
> mem_path=<optimized out>, errp=<optimized out>, errp@entry=0x555556e210d8 
> <error_fatal>)
>     at ../hw/core/machine.c:1547
> #15 0x0000555555b020ed in qemu_init_board () at ../system/vl.c:2613
> #16 qmp_x_exit_preconfig (errp=0x555556e210d8 <error_fatal>) at 
> ../system/vl.c:2705
> #17 0x0000555555b0611e in qemu_init (argc=<optimized out>, argv=<optimized 
> out>) at ../system/vl.c:3739
> #18 0x0000555555897ca9 in main (argc=<optimized out>, argv=<optimized out>) 
> at ../system/main.c:47
>
> The problem is that 'cs->kvm_state' is NULL here
>

After some investigation it seems that kvm_state is not yet committed 
at this point. Shame, because GDB showed me that we have already pass 
the kvm_accel_instance_init() in accel/kvm/kvm-all.c that sets the 
value "msr_energy.enable" in kvm_state...

So should I dig more to still do the sanity check in kvm_cpu_realizefn() 
or should I already move the RAPL feature  from -kvm to -cpu 
like suggested by Zhao from Intel and then access it from the CPUState ?

The last one would require more work but if I can skip a new iteration 
because I would need to do it anyway that would save me time in this end. 

Thanks

Regards,
Anthony