linux-kernel - Re: [PATCH v3 05/27] KVM: VMX: Disable FRED if FRED consistency checks fail

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Message-ID: <ZxdmxC92KmMQVYNU@intel.com>
Date: Tue, 22 Oct 2024 16:48:04 +0800
From: Chao Gao <chao.gao@...el.com>
To: "Xin Li (Intel)" <xin@...or.com>
CC: <kvm@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<linux-doc@...r.kernel.org>, <seanjc@...gle.com>, <pbonzini@...hat.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>
Subject: Re: [PATCH v3 05/27] KVM: VMX: Disable FRED if FRED consistency
 checks fail

On Mon, Sep 30, 2024 at 10:00:48PM -0700, Xin Li (Intel) wrote:
>From: Xin Li <xin3.li@...el.com>
>
>Do not virtualize FRED if FRED consistency checks fail.
>
>Either on broken hardware, or when run KVM on top of another hypervisor
>before the underlying hypervisor implements nested FRED correctly.
>
>Suggested-by: Chao Gao <chao.gao@...el.com>
>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>

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

one nit below,

>---
> arch/x86/kvm/vmx/capabilities.h | 7 +++++++
> arch/x86/kvm/vmx/vmx.c          | 3 +++
> 2 files changed, 10 insertions(+)
>
>diff --git a/arch/x86/kvm/vmx/capabilities.h b/arch/x86/kvm/vmx/capabilities.h
>index e8f3ad0f79ee..2962a3bb9747 100644
>--- a/arch/x86/kvm/vmx/capabilities.h
>+++ b/arch/x86/kvm/vmx/capabilities.h
>@@ -400,6 +400,13 @@ static inline bool vmx_pebs_supported(void)
> 	return boot_cpu_has(X86_FEATURE_PEBS) && kvm_pmu_cap.pebs_ept;
> }
> 
>+static inline bool cpu_has_vmx_fred(void)
>+{
>+	/* No need to check FRED VM exit controls. */

how about:

	/*
	 * setup_vmcs_config() guarantees FRED VM-entry/exit controls are
	 * either all set or none. So, no need to check FRED VM-exit controls.
	 */

It is better to call out the reason.

>+	return boot_cpu_has(X86_FEATURE_FRED) &&
>+		(vmcs_config.vmentry_ctrl & VM_ENTRY_LOAD_IA32_FRED);
>+}
>+