linux-kernel - Re: [PATCH v4 02/19] KVM: VMX: Initialize VM entry/exit FRED controls in vmcs

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Message-ID: <Z/y8DamYKsutPHvo@intel.com>
Date: Mon, 14 Apr 2025 15:41:01 +0800
From: Chao Gao <chao.gao@...el.com>
To: "Xin Li (Intel)" <xin@...or.com>
CC: <pbonzini@...hat.com>, <seanjc@...gle.com>, <kvm@...r.kernel.org>,
	<linux-doc@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<corbet@....net>, <tglx@...utronix.de>, <mingo@...hat.com>, <bp@...en8.de>,
	<dave.hansen@...ux.intel.com>, <x86@...nel.org>, <hpa@...or.com>,
	<andrew.cooper3@...rix.com>, <luto@...nel.org>, <peterz@...radead.org>,
	<xin3.li@...el.com>
Subject: Re: [PATCH v4 02/19] KVM: VMX: Initialize VM entry/exit FRED
 controls in vmcs_config

>diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
>index f1348b140e7c..e38545d0dd17 100644
>--- a/arch/x86/kvm/vmx/vmx.c
>+++ b/arch/x86/kvm/vmx/vmx.c
>@@ -2634,12 +2634,15 @@ static int setup_vmcs_config(struct vmcs_config *vmcs_conf,
> 		{ VM_ENTRY_LOAD_IA32_EFER,		VM_EXIT_LOAD_IA32_EFER },
> 		{ VM_ENTRY_LOAD_BNDCFGS,		VM_EXIT_CLEAR_BNDCFGS },
> 		{ VM_ENTRY_LOAD_IA32_RTIT_CTL,		VM_EXIT_CLEAR_IA32_RTIT_CTL },
>+		{ VM_ENTRY_LOAD_IA32_FRED,		VM_EXIT_ACTIVATE_SECONDARY_CONTROLS },

This line should be removed. It enforces that "Activate secondary controls"
is supported iff FRED is supported, which isn't true.

Bit 3 of 2nd VM-exit controls is "Prematurely busy shadow stack". Some CPUs
support it, but not FRED.