linux-kernel - [PATCH v7 12/26] KVM: x86: Report XSS as to-be-saved if there are supported features

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Message-Id: <20231124055330.138870-13-weijiang.yang@intel.com>
Date:   Fri, 24 Nov 2023 00:53:16 -0500
From:   Yang Weijiang <weijiang.yang@...el.com>
To:     seanjc@...gle.com, pbonzini@...hat.com, dave.hansen@...el.com,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     peterz@...radead.org, chao.gao@...el.com,
        rick.p.edgecombe@...el.com, mlevitsk@...hat.com,
        john.allen@....com, weijiang.yang@...el.com
Subject: [PATCH v7 12/26] KVM: x86: Report XSS as to-be-saved if there are supported features

From: Sean Christopherson <seanjc@...gle.com>

Add MSR_IA32_XSS to list of MSRs reported to userspace if supported_xss
is non-zero, i.e. KVM supports at least one XSS based feature.

Before enabling CET virtualization series, guest IA32_MSR_XSS is
guaranteed to be 0, i.e., XSAVES/XRSTORS is executed in non-root mode
with XSS == 0, which equals to the effect of XSAVE/XRSTOR.

Signed-off-by: Sean Christopherson <seanjc@...gle.com>
Signed-off-by: Yang Weijiang <weijiang.yang@...el.com>
Reviewed-by: Maxim Levitsky <mlevitsk@...hat.com>
---
 arch/x86/kvm/x86.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 360f4b8a4944..f7d4cc61bc55 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1464,6 +1464,7 @@ static const u32 msrs_to_save_base[] = {
 	MSR_IA32_UMWAIT_CONTROL,
 
 	MSR_IA32_XFD, MSR_IA32_XFD_ERR,
+	MSR_IA32_XSS,
 };
 
 static const u32 msrs_to_save_pmu[] = {
@@ -7317,6 +7318,10 @@ static void kvm_probe_msr_to_save(u32 msr_index)
 		if (!(kvm_get_arch_capabilities() & ARCH_CAP_TSX_CTRL_MSR))
 			return;
 		break;
+	case MSR_IA32_XSS:
+		if (!kvm_caps.supported_xss)
+			return;
+		break;
 	default:
 		break;
 	}
-- 
2.27.0