linux-kernel - Re: [PATCH 14/21] KVM: TDX: Implement hooks to propagate changes of TDP MMU mirror page table

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Message-ID: <Zt+mVAn1bnv/CxlK@yzhao56-desk.sh.intel.com>
Date: Tue, 10 Sep 2024 09:52:20 +0800
From: Yan Zhao <yan.y.zhao@...el.com>
To: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
CC: "kvm@...r.kernel.org" <kvm@...r.kernel.org>, "pbonzini@...hat.com"
	<pbonzini@...hat.com>, "seanjc@...gle.com" <seanjc@...gle.com>, "Huang, Kai"
	<kai.huang@...el.com>, "nik.borisov@...e.com" <nik.borisov@...e.com>,
	"dmatlack@...gle.com" <dmatlack@...gle.com>, "isaku.yamahata@...il.com"
	<isaku.yamahata@...il.com>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 14/21] KVM: TDX: Implement hooks to propagate changes of
 TDP MMU mirror page table

On Tue, Sep 10, 2024 at 05:03:57AM +0800, Edgecombe, Rick P wrote:
> On Fri, 2024-09-06 at 14:10 +1200, Huang, Kai wrote:
...
> > > +        * which causes gmem invalidation to zap all spte.
> > > +        * Population is only allowed after KVM_TDX_INIT_VM.
> > > +        */
> > 
> > What does the second sentence ("Population ...")  meaning?  Why is it 
> > relevant here?
> > 
> How about:
> /*
>  * HKID is released after all private pages have been removed,
>  * and set before any might be populated. Warn if zapping is
>  * attempted when there can't be anything populated in the private
>  * EPT.
>  */
> 
> But actually, I wonder if we need to remove the KVM_BUG_ON(). I think if you did
> a KVM_PRE_FAULT_MEMORY and then deleted the memslot you could hit it?
If we disallow vCPU creation before TD initialization, as discussed in [1],
the BUG_ON should not be hit.

[1] https://lore.kernel.org/all/ZtAU7FIV2Xkw+L3O@yzhao56-desk.sh.intel.com/