Re: [PATCH kernel] KVM: PPC: Book3S: Merge powerpc's debugfs entry content into generic entry

On 04/09/2021 00:28, Fabiano Rosas wrote:
> Alexey Kardashevskiy <[email protected]> writes:
> 
>> At the moment the generic KVM code creates an "%pid-%fd" entry per a KVM
>> instance; and the PPC HV KVM creates its own at "vm%pid".
>>
>> The rproblems with the PPC entries are:
>> 1. they do not allow multiple VMs in the same process (which is extremely
>> rare case mostly used by syzkaller fuzzer);
>> 2. prone to race bugs like the generic KVM code had fixed in
>> commit 85cd39af14f4 ("KVM: Do not leak memory for duplicate debugfs
>> directories").
>>
>> This defines kvm_arch_create_kvm_debugfs() similar to one for vcpus.
> 
> I think kvm_arch_create_vm_debugfs is a bit mode accurate?


ah yes, it is better.

>                          ^
>> This defines 2 hooks in kvmppc_ops for allowing specific KVM
>> implementations to add necessary entries.
>>
>> This makes use of already existing kvm_arch_create_vcpu_debugfs.
>>
>> This removes no more used debugfs_dir pointers from PPC kvm_arch structs.
>>
>> Suggested-by: Fabiano Rosas <[email protected]>
>> Signed-off-by: Alexey Kardashevskiy <[email protected]>
> 
> ...
> 
>> diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
>> index c8f12b056968..325b388c725a 100644
>> --- a/arch/powerpc/kvm/book3s_hv.c
>> +++ b/arch/powerpc/kvm/book3s_hv.c
>> @@ -2771,19 +2771,14 @@ static const struct file_operations debugfs_timings_ops = {
>>   };
>>   
>>   /* Create a debugfs directory for the vcpu */
>> -static void debugfs_vcpu_init(struct kvm_vcpu *vcpu, unsigned int id)
>> +static void kvmppc_arch_create_vcpu_debugfs_hv(struct kvm_vcpu *vcpu, struct dentry *debugfs_dentry)
> 
> This could lose the 'arch' since it is already inside our code and
> accessed only via ops. I see that we already have a
> kvmppc_create_vcpu_debugfs that's used for some BookE processor, this

Ouch, missed kvmppc_create_vcpu_debugfs(). Good eye :)


> would make:
> 
> kvmppc_create_vcpu_debugfs
> kvmppc_create_vcpu_debugfs_hv
> kvmppc_create_vcpu_debugfs_pr (possibly)
> 
> which perhaps is more consistent.


Or  kvm_arch_vm_ioctl_hv(). I really like having "arch" in the name, 
tells right away what it is about. "kvmppc" might be excessive. Thanks,



>>   {
>> -	char buf[16];
>> -	struct kvm *kvm = vcpu->kvm;
>> -
>> -	snprintf(buf, sizeof(buf), "vcpu%u", id);
>> -	vcpu->arch.debugfs_dir = debugfs_create_dir(buf, kvm->arch.debugfs_dir);
>> -	debugfs_create_file("timings", 0444, vcpu->arch.debugfs_dir, vcpu,
>> +	debugfs_create_file("timings", 0444, debugfs_dentry, vcpu,
>>   			    &debugfs_timings_ops);
>>   }
>>   
>>   #else /* CONFIG_KVM_BOOK3S_HV_EXIT_TIMING */
>> -static void debugfs_vcpu_init(struct kvm_vcpu *vcpu, unsigned int id)
>> +static void kvmppc_arch_create_vcpu_debugfs_hv(struct kvm_vcpu *vcpu, struct dentry *debugfs_dentry)
>>   {
>>   }
>>   #endif /* CONFIG_KVM_BOOK3S_HV_EXIT_TIMING */

-- 
Alexey