linux-kernel - Re: [RFC PATCH 06/12] KVM: TDX: Return -EIO, not -EINVAL, on a KVM_BUG

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Message-ID: <48743e1790220072c72d45af8d3582cdd25f4083.camel@intel.com>
Date: Thu, 28 Aug 2025 21:19:24 +0000
From: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
To: "seanjc@...gle.com" <seanjc@...gle.com>
CC: "kvm@...r.kernel.org" <kvm@...r.kernel.org>, "pbonzini@...hat.com"
	<pbonzini@...hat.com>, "Annapurve, Vishal" <vannapurve@...gle.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "Zhao, Yan Y"
	<yan.y.zhao@...el.com>, "michael.roth@....com" <michael.roth@....com>,
	"Weiny, Ira" <ira.weiny@...el.com>
Subject: Re: [RFC PATCH 06/12] KVM: TDX: Return -EIO, not -EINVAL, on a
 KVM_BUG_ON() condition

On Thu, 2025-08-28 at 14:00 -0700, Sean Christopherson wrote:
> But that's not actually what the code does.  The lockdep assert won't trip because
> KVM never removes S-EPT entries under read-lock:

Right

> 
> 		if (is_mirror_sp(sp)) {
> 			KVM_BUG_ON(shared, kvm);
> 			remove_external_spte(kvm, gfn, old_spte, level);
> 		}
> 
> Not because KVM actually guarantees -EBUSY is avoided.  So the current code is
> flawed, it just doesn't cause problems.

Flawed, as in the lockdep should assert regardless of EBUSY? Seems good to me.
Probably if we wanted to try to call tdx_sept_remove_private_spte() under read
lock with special plans to avoid EBUSY we should think twice anyway.