linux-kernel - Re: [PATCH v2 22/24] KVM: TDX: Finalize VM initialization

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Message-ID: <CABgObfZMR5y7T_dv-V8ng0dv=L00XgUmaDm-V9Y1aVEuz=0anw@mail.gmail.com>
Date: Tue, 7 Jan 2025 15:02:28 +0100
From: Paolo Bonzini <pbonzini@...hat.com>
To: Yan Zhao <yan.y.zhao@...el.com>
Cc: seanjc@...gle.com, kvm@...r.kernel.org, dave.hansen@...ux.intel.com, 
	rick.p.edgecombe@...el.com, kai.huang@...el.com, adrian.hunter@...el.com, 
	reinette.chatre@...el.com, xiaoyao.li@...el.com, tony.lindgren@...el.com, 
	binbin.wu@...ux.intel.com, dmatlack@...gle.com, isaku.yamahata@...el.com, 
	isaku.yamahata@...il.com, nik.borisov@...e.com, linux-kernel@...r.kernel.org, 
	x86@...nel.org
Subject: Re: [PATCH v2 22/24] KVM: TDX: Finalize VM initialization

On Tue, Jan 7, 2025 at 8:45 AM Yan Zhao <yan.y.zhao@...el.com> wrote:
> > @@ -1715,8 +1715,8 @@ static int tdx_gmem_post_populate(struct kvm *kvm, gfn_t gfn, kvm_pfn_t pfn,
> >               goto out;
> >       }
> > -     WARN_ON_ONCE(!atomic64_read(&kvm_tdx->nr_premapped));
> > -     atomic64_dec(&kvm_tdx->nr_premapped);
> > +     if (!WARN_ON_ONCE(!atomic64_read(&kvm_tdx->nr_premapped)))
> > +             atomic64_dec(&kvm_tdx->nr_premapped);
> One concern here.
> If tdx_gmem_post_populate() is called when kvm_tdx->nr_premapped is 0, it will
> trigger the WARN_ON here, indicating that something has gone wrong.
> Should KVM refuse to start the TD in this case?
>
> If we don't decrease kvm_tdx->nr_premapped in that case, it will remain 0,
> allowing it to pass the check in tdx_td_finalize().

Let's make it a KVM_BUG_ON then.

Paolo