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

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Date:   Thu, 31 Mar 2022 15:23:44 -0700
From:   David Matlack <dmatlack@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     LKML <linux-kernel@...r.kernel.org>, kvm list <kvm@...r.kernel.org>
Subject: Re: [PATCH] KVM: MMU: propagate alloc_workqueue failure

On Thu, Mar 31, 2022 at 2:34 AM Paolo Bonzini <pbonzini@...hat.com> wrote:
>
> 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.

Oh ok, that makes sense. I agree it's a matter of taste.

>
> >> +    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.

Sounds good.

>
> Paolo
>