linux-kernel - Re: [PATCH kernel] KVM: PPC: Book3S HV: Make unique debugfs nodename

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Message-ID: <87lf4gv0hf.fsf@linux.ibm.com>
Date:   Wed, 01 Sep 2021 11:23:08 -0300
From:   Fabiano Rosas <farosas@...ux.ibm.com>
To:     Alexey Kardashevskiy <aik@...abs.ru>,
        Michael Ellerman <mpe@...erman.id.au>
Cc:     linux-kernel@...r.kernel.org, kvm-ppc@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, Paul Mackerras <paulus@...abs.org>
Subject: Re: [PATCH kernel] KVM: PPC: Book3S HV: Make unique debugfs nodename

Alexey Kardashevskiy <aik@...abs.ru> writes:

> On 24/08/2021 18:37, Alexey Kardashevskiy wrote:
>> 
>> 
>> On 18/08/2021 08:20, Fabiano Rosas wrote:
>>> Alexey Kardashevskiy <aik@...abs.ru> writes:
>>>
>>>> On 07/07/2021 14:13, Alexey Kardashevskiy wrote:
>>>
>>>> alternatively move this debugfs stuff under the platform-independent
>>>> directory, how about that?
>>>
>>> That's a good idea. I only now realized we have two separate directories
>>> for the same guest:
>>>
>>> $ ls /sys/kernel/debug/kvm/ | grep $pid
>>> 19062-11
>>> vm19062
>>>
>>> Looks like we would have to implement kvm_arch_create_vcpu_debugfs for
>>> the vcpu information and add a similar hook for the vm.
>> 
>> Something like that. From the git history, it looks like the ppc folder 
>> was added first and then the generic kvm folder was added but apparently 
>> they did not notice the ppc one due to natural reasons :)
>> 
>> If you are not too busy, can you please merge the ppc one into the 
>> generic one and post the patch, so we won't need to fix these 
>> duplication warnings again? Thanks,
>
>
>
> Turns out it is not that straight forward as I thought as the common KVM 
> debugfs entry is created after PPC HV KVM created its own and there is 
> no obvious way to change the order (no "post init" hook in
> kvmppc_ops).

That is why I mentioned creating a hook similar to
kvm_create_vcpu_debugfs in the common KVM code. kvm_create_vm_debugfs or
something.

Alternatively, maybe kvm_create_vm_debugfs could be moved earlier into
kvm_create_vm, before kvm_arch_post_init_vm and we could move our code
into kvm_arch_post_init_vm.

>
> Also, unlike the common KVM debugfs setup, we do not allocate structures 
> to support debugfs nodes so we do not leak anything to bother with a 
> mutex like 85cd39af14f4 did.
>
> So I'd stick to the original patch to reduce the noise in the dmesg, and 
> it also exposes lpid which I find rather useful for finding the right 
> partition scope tree in partition_tb.
>
> Michael?
>
>
>> 
>> 
>> 
>>>>> ---
>>>>>    arch/powerpc/kvm/book3s_hv.c | 2 +-
>>>>>    1 file changed, 1 insertion(+), 1 deletion(-)
>>>>>
>>>>> diff --git a/arch/powerpc/kvm/book3s_hv.c 
>>>>> b/arch/powerpc/kvm/book3s_hv.c
>>>>> index 1d1fcc290fca..0223ddc0eed0 100644
>>>>> --- a/arch/powerpc/kvm/book3s_hv.c
>>>>> +++ b/arch/powerpc/kvm/book3s_hv.c
>>>>> @@ -5227,7 +5227,7 @@ static int kvmppc_core_init_vm_hv(struct kvm 
>>>>> *kvm)
>>>>>        /*
>>>>>         * Create a debugfs directory for the VM
>>>>>         */
>>>>> -    snprintf(buf, sizeof(buf), "vm%d", current->pid);
>>>>> +    snprintf(buf, sizeof(buf), "vm%d-lp%ld", current->pid, lpid);
>>>>>        kvm->arch.debugfs_dir = debugfs_create_dir(buf, 
>>>>> kvm_debugfs_dir);
>>>>>        kvmppc_mmu_debugfs_init(kvm);
>>>>>        if (radix_enabled())
>>>>>
>>