linux-kernel - Re: [PATCH] KVM: MMU: propagate alloc

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Date:   Thu, 31 Mar 2022 11:34:35 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     David Matlack <dmatlack@...gle.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH] KVM: MMU: propagate alloc_workqueue failure

On 3/31/22 01:51, David Matlack wrote:
>> -void kvm_mmu_init_vm(struct kvm *kvm)
>> +int kvm_mmu_init_vm(struct kvm *kvm)
>>   {
>>   	struct kvm_page_track_notifier_node *node = &kvm->arch.mmu_sp_tracker;
>> +	int r;
>>   
>> +	INIT_LIST_HEAD(&kvm->arch.active_mmu_pages);
>> +	INIT_LIST_HEAD(&kvm->arch.zapped_obsolete_pages);
>> +	INIT_LIST_HEAD(&kvm->arch.lpage_disallowed_mmu_pages);
> 
> I agree with moving these but that should probably be done in a separate
> commit.

Ok.

>> -	kvm->arch.tdp_mmu_zap_wq =
>> -		alloc_workqueue("kvm", WQ_UNBOUND|WQ_MEM_RECLAIM|WQ_CPU_INTENSIVE, 0);
>> -
>> -	return true;
>> +	kvm->arch.tdp_mmu_zap_wq = wq;
> 
> Suggest moving this to just after checking the return value of
> alloc_workqueue().

This is intentional, in case we have other future allocations, to avoid 
having to NULL out the field in the unwind path.  It's a matter of taste 
I guess.

>> +	return 1;
> 
> Perhaps return 0 until we have a reason to differentiate the 2 cases.

Yeah, though I wanted to preserve the previous behavior.

>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>> index fe2171b11441..89b6efb7f504 100644
>> --- a/arch/x86/kvm/x86.c
>> +++ b/arch/x86/kvm/x86.c
>> @@ -11629,12 +11629,13 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
>>   
>>   	ret = kvm_page_track_init(kvm);
>>   	if (ret)
>> -		return ret;
>> +		goto out;
> 
> nit: This goto is unnecessary.

True, but I prefer to be consistent in using "goto" so that any future 
additions are careful about preserving the chain.

Paolo