linux-kernel - Re: [PATCH v9 22/22] KVM: nVMX: Enable VMX FRED controls

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Message-ID: <aRVOjoRNNmI8/wa4@intel.com>
Date: Thu, 13 Nov 2025 11:20:46 +0800
From: Chao Gao <chao.gao@...el.com>
To: "Xin Li (Intel)" <xin@...or.com>
CC: <linux-kernel@...r.kernel.org>, <kvm@...r.kernel.org>,
	<linux-doc@...r.kernel.org>, <pbonzini@...hat.com>, <seanjc@...gle.com>,
	<corbet@....net>, <tglx@...utronix.de>, <mingo@...hat.com>, <bp@...en8.de>,
	<dave.hansen@...ux.intel.com>, <x86@...nel.org>, <hpa@...or.com>,
	<luto@...nel.org>, <peterz@...radead.org>, <andrew.cooper3@...rix.com>,
	<hch@...radead.org>, <sohil.mehta@...el.com>
Subject: Re: [PATCH v9 22/22] KVM: nVMX: Enable VMX FRED controls

On Sun, Oct 26, 2025 at 01:19:10PM -0700, Xin Li (Intel) wrote:
>From: Xin Li <xin3.li@...el.com>
>
>Permit use of VMX FRED controls in nested VMX now that support for nested
>FRED is implemented.
>
>Signed-off-by: Xin Li <xin3.li@...el.com>
>Signed-off-by: Xin Li (Intel) <xin@...or.com>
>Tested-by: Shan Kang <shan.kang@...el.com>
>Tested-by: Xuelian Guo <xuelian.guo@...el.com>

Reviewed-by: Chao Gao <chao.gao@...el.com>

>---
>
>Change in v5:
>* Add TB from Xuelian Guo.
>---
> arch/x86/kvm/vmx/nested.c | 5 +++--
> arch/x86/kvm/vmx/vmx.c    | 1 +
> 2 files changed, 4 insertions(+), 2 deletions(-)
>
>diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
>index 37ab8250dd31..655257b34d15 100644
>--- a/arch/x86/kvm/vmx/nested.c
>+++ b/arch/x86/kvm/vmx/nested.c
>@@ -7397,7 +7397,8 @@ static void nested_vmx_setup_exit_ctls(struct vmcs_config *vmcs_conf,
> 		 * advertise any feature in it to nVMX until its nVMX support
> 		 * is ready.
> 		 */

Shouldn't this comment be removed? I suppose it was a note to reviewers
explaining why it's hard-coded to 0. Since some features have been added, the
comment can be dropped.

>-		msrs->secondary_exit_ctls &= 0;
>+		msrs->secondary_exit_ctls &= SECONDARY_VM_EXIT_SAVE_IA32_FRED |
>+					     SECONDARY_VM_EXIT_LOAD_IA32_FRED;
> 	}
> }
> 
>@@ -7413,7 +7414,7 @@ static void nested_vmx_setup_entry_ctls(struct vmcs_config *vmcs_conf,
> 		VM_ENTRY_IA32E_MODE |
> #endif
> 		VM_ENTRY_LOAD_IA32_PAT | VM_ENTRY_LOAD_BNDCFGS |
>-		VM_ENTRY_LOAD_CET_STATE;
>+		VM_ENTRY_LOAD_CET_STATE | VM_ENTRY_LOAD_IA32_FRED;
> 	msrs->entry_ctls_high |=
> 		(VM_ENTRY_ALWAYSON_WITHOUT_TRUE_MSR | VM_ENTRY_LOAD_IA32_EFER |
> 		 VM_ENTRY_LOAD_IA32_PERF_GLOBAL_CTRL);
>diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
>index 04442f869abb..8f3805a71a97 100644
>--- a/arch/x86/kvm/vmx/vmx.c
>+++ b/arch/x86/kvm/vmx/vmx.c
>@@ -7994,6 +7994,7 @@ static void nested_vmx_cr_fixed1_bits_update(struct kvm_vcpu *vcpu)
> 
> 	entry = kvm_find_cpuid_entry_index(vcpu, 0x7, 1);
> 	cr4_fixed1_update(X86_CR4_LAM_SUP,    eax, feature_bit(LAM));
>+	cr4_fixed1_update(X86_CR4_FRED,       eax, feature_bit(FRED));
> 
> #undef cr4_fixed1_update
> }
>-- 
>2.51.0
>