linux-kernel - Re: [PATCH 11/16] KVM: TDX: Always block INIT/SIPI

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Message-ID: <47c3f636becd74cb2f6183f76e7839d4ecc64578.camel@intel.com>
Date: Thu, 9 Jan 2025 04:01:03 +0000
From: "Huang, Kai" <kai.huang@...el.com>
To: "seanjc@...gle.com" <seanjc@...gle.com>, "binbin.wu@...ux.intel.com"
	<binbin.wu@...ux.intel.com>
CC: "Gao, Chao" <chao.gao@...el.com>, "Edgecombe, Rick P"
	<rick.p.edgecombe@...el.com>, "Li, Xiaoyao" <xiaoyao.li@...el.com>, "Chatre,
 Reinette" <reinette.chatre@...el.com>, "Hunter, Adrian"
	<adrian.hunter@...el.com>, "tony.lindgren@...ux.intel.com"
	<tony.lindgren@...ux.intel.com>, "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"pbonzini@...hat.com" <pbonzini@...hat.com>, "Yamahata, Isaku"
	<isaku.yamahata@...el.com>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "Zhao, Yan Y" <yan.y.zhao@...el.com>
Subject: Re: [PATCH 11/16] KVM: TDX: Always block INIT/SIPI

On Thu, 2025-01-09 at 11:20 +0800, Binbin Wu wrote:
> 
> 
> On 1/9/2025 10:46 AM, Huang, Kai wrote:
> > On Thu, 2025-01-09 at 10:26 +0800, Binbin Wu wrote:
> > > > > > I think we can just say TDX doesn't support vcpu reset no matter due to
> > > > > > INIT event or not.
> > > > That's not entirely accurate either though.  TDX does support KVM's version of
> > > > RESET, because KVM's RESET is "power-on", i.e. vCPU creation.  Emulation of
> > > > runtime RESET is userspace's responsibility.
> > > > 
> > > > The real reason why KVM doesn't do anything during KVM's RESET is that what
> > > > little setup KVM does/can do needs to be defered until after guest CPUID is
> > > > configured.
> > > > 
> > > > KVM should also WARN if a TDX vCPU gets INIT, no?
> > > There was a KVM_BUG_ON() if a TDX vCPU gets INIT in v19, and later it was
> > > removed during the cleanup about removing WARN_ON_ONCE() and KVM_BUG_ON().
> > > 
> > > Since INIT/SIPI are always blocked for TDX guests, a delivery of INIT
> > > event is a KVM bug and a WARN_ON_ONCE() is appropriate for this case.
> > Can TDX guest issue INIT via IPI?  Perhaps KVM_BUG_ON() is safer?
> TDX guests are not expected to issue INIT, but it could in theory.
> It seems no serous impact if guest does it, not sure it needs to kill the
> VM or not.
> 
> Also, in this patch, for TDX kvm_apic_init_sipi_allowed() is always
> returning false, so vt_vcpu_reset() will not be called with init=true.
> Adding a WARN_ON_ONCE() is the guard for the KVM's logic itself,
> not the guard for guest behavior.
> 

Yeah agreed.  I replied too early before looking at the patch.