linux-kernel - Re: [PATCH v19 093/130] KVM: TDX: Implements vcpu request_immediate

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Date: Mon, 1 Apr 2024 23:52:54 -0700
From: Isaku Yamahata <isaku.yamahata@...el.com>
To: Chao Gao <chao.gao@...el.com>
Cc: isaku.yamahata@...el.com, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org, isaku.yamahata@...il.com,
	Paolo Bonzini <pbonzini@...hat.com>, erdemaktas@...gle.com,
	Sean Christopherson <seanjc@...gle.com>,
	Sagi Shahar <sagis@...gle.com>, Kai Huang <kai.huang@...el.com>,
	chen.bo@...el.com, hang.yuan@...el.com, tina.zhang@...el.com,
	isaku.yamahata@...ux.intel.com
Subject: Re: [PATCH v19 093/130] KVM: TDX: Implements vcpu
 request_immediate_exit

On Fri, Mar 29, 2024 at 09:54:04AM +0800,
Chao Gao <chao.gao@...el.com> wrote:

> On Mon, Feb 26, 2024 at 12:26:35AM -0800, isaku.yamahata@...el.com wrote:
> >From: Isaku Yamahata <isaku.yamahata@...el.com>
> >
> >Now we are able to inject interrupts into TDX vcpu, it's ready to block TDX
> >vcpu.  Wire up kvm x86 methods for blocking/unblocking vcpu for TDX.  To
> >unblock on pending events, request immediate exit methods is also needed.
> 
> TDX doesn't support this immediate exit. It is considered as a potential
> attack to TDs. TDX module deploys 0/1-step mitigations to prevent this.
> Even KVM issues a self-IPI before TD-entry, TD-exit will happen after
> the guest runs a random number of instructions.
> 
> KVM shouldn't request immediate exits in the first place. Just emit a
> warning if KVM tries to do this.

0ec3d6d1f169
("KVM: x86: Fully defer to vendor code to decide how to force immediate exit")
removed the hook.  This patch will be dropped and tdx_vcpu_run() will ignore
force_immediate_exit.
-- 
Isaku Yamahata <isaku.yamahata@...el.com>