linux-kernel - Re: [PATCH v9 07/22] KVM: VMX: Initialize VMCS FRED fields

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Message-ID: <aR0vK3z1owwM8X8H@intel.com>
Date: Wed, 19 Nov 2025 10:44:59 +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 07/22] KVM: VMX: Initialize VMCS FRED fields

On Sun, Oct 26, 2025 at 01:18:55PM -0700, Xin Li (Intel) wrote:
>From: Xin Li <xin3.li@...el.com>
>
>Initialize host VMCS FRED fields with host FRED MSRs' value and
>guest VMCS FRED fields to 0.
>
>FRED CPU state is managed in 9 new FRED MSRs:
>        IA32_FRED_CONFIG,
>        IA32_FRED_STKLVLS,
>        IA32_FRED_RSP0,
>        IA32_FRED_RSP1,
>        IA32_FRED_RSP2,
>        IA32_FRED_RSP3,
>        IA32_FRED_SSP1,
>        IA32_FRED_SSP2,
>        IA32_FRED_SSP3,
>as well as a few existing CPU registers and MSRs:
>        CR4.FRED,
>        IA32_STAR,
>        IA32_KERNEL_GS_BASE,
>        IA32_PL0_SSP (also known as IA32_FRED_SSP0).
>
>CR4, IA32_KERNEL_GS_BASE and IA32_STAR are already well managed.
>Except IA32_FRED_RSP0 and IA32_FRED_SSP0, all other FRED CPU state
>MSRs have corresponding VMCS fields in both the host-state and
>guest-state areas.  So KVM just needs to initialize them, and with
>proper VM entry/exit FRED controls, a FRED CPU will keep tracking
>host and guest FRED CPU state in VMCS automatically.
>
>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>

one nit below,

>@@ -8717,6 +8748,11 @@ __init int vmx_hardware_setup(void)
> 
> 	kvm_caps.inapplicable_quirks &= ~KVM_X86_QUIRK_IGNORE_GUEST_PAT;
> 
>+	if (kvm_cpu_cap_has(X86_FEATURE_FRED)) {
>+		rdmsrl(MSR_IA32_FRED_CONFIG, kvm_host.fred_config);
>+		rdmsrl(MSR_IA32_FRED_STKLVLS, kvm_host.fred_stklvls);

s/rdmsrl/rdmsrq

>+	}
>+
> 	return r;
> }
> 
>diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
>index f3dc77f006f9..0c1fbf75442b 100644
>--- a/arch/x86/kvm/x86.h
>+++ b/arch/x86/kvm/x86.h
>@@ -52,6 +52,9 @@ struct kvm_host_values {
> 	u64 xss;
> 	u64 s_cet;
> 	u64 arch_capabilities;
>+
>+	u64 fred_config;
>+	u64 fred_stklvls;
> };
> 
> void kvm_spurious_fault(void);
>-- 
>2.51.0
>