linux-kernel - Re: [PATCH 2/5] KVM: TDX: Exit with MEMORY_FAULT on unexpected pending S-EPT Violation

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Message-ID: <42a1dcc7f8607e526f09c758876e5967eb0e42ae.camel@intel.com>
Date: Tue, 29 Jul 2025 23:13:58 +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>, "oliver.upton@...ux.dev"
	<oliver.upton@...ux.dev>, "Annapurve, Vishal" <vannapurve@...gle.com>, "Li,
 Xiaoyao" <xiaoyao.li@...el.com>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "kvmarm@...ts.linux.dev"
	<kvmarm@...ts.linux.dev>, "linux-arm-kernel@...ts.infradead.org"
	<linux-arm-kernel@...ts.infradead.org>, "maz@...nel.org" <maz@...nel.org>,
	"Hunter, Adrian" <adrian.hunter@...el.com>, "nik.borisov@...e.com"
	<nik.borisov@...e.com>, "pbonzini@...hat.com" <pbonzini@...hat.com>
Subject: Re: [PATCH 2/5] KVM: TDX: Exit with MEMORY_FAULT on unexpected
 pending S-EPT Violation

On Tue, 2025-07-29 at 16:08 -0700, Sean Christopherson wrote:
> > If userspace runs the vCPU again then an EPT violation gets triggered again,
> > which again gets kicked out to userspace. The new check will prevent it from
> > getting into the fault handler, right?
> 
> Yes?  But I'm confused about why you mentioned vm_dead, and why you're calling
> this a "new check".  This effectively does two things: drops kvm_vm_dead() and
> switches from EOI => EFAULT.  _If_ setting vm_dead was necessary, then we have
> a
> problem.
> 
> I assume by "The vm_dead was added" you really mean "forcing an exit to
> userspace",
> and that kvm_vm_dead()+EIO was a somewhat arbitrary way of forcing an exit?

Sorry, yes vm_dead prevents an EPT violation loop but not the KVM_BUG_ON(). The
whole if clause prevents the KVM_BUG_ON(). Your patch prevents the ept violation
loop in a better way.