linux-kernel - Re: [RFC PATCH 8/9] x86/kvm/vmx: Initialize SPEC

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Date:   Sun, 15 Jan 2023 22:20:23 +0800
From:   Chao Gao <chao.gao@...el.com>
To:     Zhang Chen <chen.zhang@...el.com>
CC:     <x86@...nel.org>, <linux-kernel@...r.kernel.org>,
        <kvm@...r.kernel.org>,
        Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "Borislav Petkov" <bp@...en8.de>, Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [RFC PATCH 8/9] x86/kvm/vmx: Initialize SPEC_CTRL MASK for RRSBA

On Sun, Dec 11, 2022 at 12:00:45AM +0800, Zhang Chen wrote:
>VMMs can address mitigations issues in migration pool by applying
>the needed controls whenever the guest is operating on a newer
>processor. If a guest is using retpoline to mitigate intra-mode BTI
>in CPL0, the VMM can set RRSBA_DIS_S when the guest runs on hardware
>which enumerates RRSBA.
>
>Signed-off-by: Zhang Chen <chen.zhang@...el.com>
>---
> arch/x86/kvm/vmx/vmx.c | 57 +++++++++++++++++++++++++++++++++++++++++-
> 1 file changed, 56 insertions(+), 1 deletion(-)
>
>diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
>index 6ed6b743be0e..fb0f3b1639b9 100644
>--- a/arch/x86/kvm/vmx/vmx.c
>+++ b/arch/x86/kvm/vmx/vmx.c
>@@ -2007,6 +2007,20 @@ static int vmx_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
> 			return 1;
> 		msr_info->data = vmx->msr_virtual_enumeration;
> 		break;
>+	case MSR_VIRTUAL_MITIGATION_ENUM:
>+		if (!msr_info->host_initiated &&
>+		    !(vmx->msr_virtual_enumeration &
>+		    VIRT_ENUM_MITIGATION_CTRL_SUPPORT))
>+			return 1;
>+		msr_info->data = vmx->msr_virtual_mitigation_enum;
>+		break;
>+	case MSR_VIRTUAL_MITIGATION_CTRL:
>+		if (!msr_info->host_initiated &&
>+		    !(vmx->msr_virtual_enumeration &
>+		    VIRT_ENUM_MITIGATION_CTRL_SUPPORT))
>+			return 1;
>+		msr_info->data = vmx->msr_virtual_mitigation_ctrl;
>+		break;
> 	default:
> 	find_uret_msr:
> 		msr = vmx_find_uret_msr(vmx, msr_info->index);
>@@ -2056,7 +2070,7 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
> 	struct vmx_uret_msr *msr;
> 	int ret = 0;
> 	u32 msr_index = msr_info->index;
>-	u64 data = msr_info->data;
>+	u64 data = msr_info->data, arch_msr;
> 	u32 index;
> 
> 	switch (msr_index) {
>@@ -2390,6 +2404,46 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
> 		vmx->msr_virtual_enumeration = data &
> 						VIRT_ENUM_MITIGATION_CTRL_SUPPORT;
> 		break;
>+	case MSR_VIRTUAL_MITIGATION_ENUM:
>+		if (msr_info->host_initiated &&
>+		    !(vmx->msr_virtual_enumeration &
>+		    VIRT_ENUM_MITIGATION_CTRL_SUPPORT))
>+			return 1;
>+		if (data & ~MITI_ENUM_SUPPORTED)
>+			return 1;
>+		vmx->msr_virtual_mitigation_enum = data;
>+		break;
>+	case MSR_VIRTUAL_MITIGATION_CTRL:
>+		if (!msr_info->host_initiated &&
>+		    !(vmx->msr_virtual_enumeration &
>+		    VIRT_ENUM_MITIGATION_CTRL_SUPPORT))
>+			return 1;
>+		if (data & ~MITI_CTRL_USED)
>+			return 1;
>+


>+		if (boot_cpu_has(X86_FEATURE_ARCH_CAPABILITIES))
>+			rdmsrl(MSR_IA32_ARCH_CAPABILITIES, arch_msr);
>+
>+		if (data & MITI_CTRL_RETPOLINE_S_USED &&
>+		    boot_cpu_has(X86_FEATURE_RRSBA_CTRL) &&
>+		    arch_msr & ARCH_CAP_RRSBA)
>+			vmx->spec_ctrl_mask |= SPEC_CTRL_RRSBA_DIS_S;
>+		else
>+			vmx->spec_ctrl_mask &= ~SPEC_CTRL_RRSBA_DIS_S;

IIUC, only above chunk belongs to this patch. Other changes should be moved
to patch 7, which deals with MSRs emulation.