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

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Date: Fri, 29 Mar 2024 09:54:04 +0800
From: Chao Gao <chao.gao@...el.com>
To: <isaku.yamahata@...el.com>
CC: <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>
Subject: Re: [PATCH v19 093/130] KVM: TDX: Implements vcpu
 request_immediate_exit

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.

>
>Signed-off-by: Isaku Yamahata <isaku.yamahata@...el.com>
>Reviewed-by: Paolo Bonzini <pbonzini@...hat.com>
>---
> arch/x86/kvm/vmx/main.c | 12 +++++++++++-
> 1 file changed, 11 insertions(+), 1 deletion(-)
>
>diff --git a/arch/x86/kvm/vmx/main.c b/arch/x86/kvm/vmx/main.c
>index f2c9d6358f9e..ee6c04959d4c 100644
>--- a/arch/x86/kvm/vmx/main.c
>+++ b/arch/x86/kvm/vmx/main.c
>@@ -372,6 +372,16 @@ static void vt_enable_irq_window(struct kvm_vcpu *vcpu)
> 	vmx_enable_irq_window(vcpu);
> }
> 
>+static void vt_request_immediate_exit(struct kvm_vcpu *vcpu)
>+{
>+	if (is_td_vcpu(vcpu)) {
>+		__kvm_request_immediate_exit(vcpu);
>+		return;
>+	}
>+
>+	vmx_request_immediate_exit(vcpu);
>+}
>+
> static u8 vt_get_mt_mask(struct kvm_vcpu *vcpu, gfn_t gfn, bool is_mmio)
> {
> 	if (is_td_vcpu(vcpu))
>@@ -549,7 +559,7 @@ struct kvm_x86_ops vt_x86_ops __initdata = {
> 	.check_intercept = vmx_check_intercept,
> 	.handle_exit_irqoff = vmx_handle_exit_irqoff,
> 
>-	.request_immediate_exit = vmx_request_immediate_exit,
>+	.request_immediate_exit = vt_request_immediate_exit,
> 
> 	.sched_in = vt_sched_in,
> 
>-- 
>2.25.1
>
>