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

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Message-ID: <Z33gjNlhGGSEngYJ@yzhao56-desk.sh.intel.com>
Date: Wed, 8 Jan 2025 10:18:52 +0800
From: Yan Zhao <yan.y.zhao@...el.com>
To: Paolo Bonzini <pbonzini@...hat.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 07, 2025 at 03:02:28PM +0100, Paolo Bonzini wrote:
> 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.

Ok. Fair enough.