linux-kernel - Re: [PATCH v12 18/24] KVM: VMX: Set host constant supervisor states to VMCS fields

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Message-ID: <aKLc4BpUm++xjv7q@intel.com>
Date: Mon, 18 Aug 2025 15:57:20 +0800
From: Chao Gao <chao.gao@...el.com>
To: <kvm@...r.kernel.org>, <linux-kernel@...r.kernel.org>
CC: <mlevitsk@...hat.com>, <rick.p.edgecombe@...el.com>,
	<weijiang.yang@...el.com>, <xin@...or.com>, Sean Christopherson
	<seanjc@...gle.com>, Mathias Krause <minipli@...ecurity.net>, John Allen
	<john.allen@....com>, Paolo Bonzini <pbonzini@...hat.com>, Thomas Gleixner
	<tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov
	<bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>, <x86@...nel.org>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH v12 18/24] KVM: VMX: Set host constant supervisor states
 to VMCS fields

> void set_cr4_guest_host_mask(struct vcpu_vmx *vmx)
>diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>index cc39ace47262..91e78c506105 100644
>--- a/arch/x86/kvm/x86.c
>+++ b/arch/x86/kvm/x86.c
>@@ -9845,6 +9845,18 @@ int kvm_x86_vendor_init(struct kvm_x86_init_ops *ops)
> 		return -EIO;
> 	}
> 
>+	if (boot_cpu_has(X86_FEATURE_SHSTK)) {
>+		rdmsrl(MSR_IA32_S_CET, kvm_host.s_cet);

This should be rdmsrq for consistency with other call sites in this file.

>+		/*
>+		 * Linux doesn't yet support supervisor shadow stacks (SSS), so
>+		 * KVM doesn't save/restore the associated MSRs, i.e. KVM may
>+		 * clobber the host values.  Yell and refuse to load if SSS is
>+		 * unexpectedly enabled, e.g. to avoid crashing the host.
>+		 */
>+		if (WARN_ON_ONCE(kvm_host.s_cet & CET_SHSTK_EN))
>+			return -EIO;
>+	}
>+
> 	memset(&kvm_caps, 0, sizeof(kvm_caps));
> 
> 	x86_emulator_cache = kvm_alloc_emulator_cache();
>diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
>index d5b039addd11..d612ddcae247 100644
>--- a/arch/x86/kvm/x86.h
>+++ b/arch/x86/kvm/x86.h
>@@ -50,6 +50,7 @@ struct kvm_host_values {
> 	u64 efer;
> 	u64 xcr0;
> 	u64 xss;
>+	u64 s_cet;
> 	u64 arch_capabilities;
> };
> 
>-- 
>2.47.1
>