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From:   Maxim Levitsky <mlevitsk@redhat.com>
To:     kvm@vger.kernel.org
Cc:     Thomas Gleixner <tglx@linutronix.de>,
        Yang Zhong <yang.zhong@intel.com>, x86@kernel.org,
        Jim Mattson <jmattson@google.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Sean Christopherson <seanjc@google.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Shuah Khan <shuah@kernel.org>,
        Guang Zeng <guang.zeng@intel.com>,
        Joerg Roedel <joro@8bytes.org>,
        Maxim Levitsky <mlevitsk@redhat.com>,
        linux-kernel@vger.kernel.org,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Ingo Molnar <mingo@redhat.com>,
        linux-kselftest@vger.kernel.org, Kees Cook <keescook@chromium.org>,
        "H. Peter Anvin" <hpa@zytor.com>, Wei Wang <wei.w.wang@intel.com>,
        Borislav Petkov <bp@alien8.de>
Subject: [PATCH RESEND v4 22/23] KVM: x86: SVM: don't save SVM state to SMRAM when VM is not long mode capable
Date:   Tue, 25 Oct 2022 15:47:40 +0300
Message-Id: <20221025124741.228045-23-mlevitsk@redhat.com>
In-Reply-To: <20221025124741.228045-1-mlevitsk@redhat.com>
References: <20221025124741.228045-1-mlevitsk@redhat.com>
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When the guest CPUID doesn't have support for long mode, 32 bit SMRAM
layout is used and it has no support for preserving EFER and/or SVM
state.

Note that this isn't relevant to running 32 bit guests on VM which is
long mode capable - such VM can still run 32 bit guests in compatibility
mode.

Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
---
 arch/x86/kvm/svm/svm.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 3004a5ff3fbf79..d22a809d923339 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -4445,6 +4445,14 @@ static int svm_enter_smm(struct kvm_vcpu *vcpu, union kvm_smram *smram)
 	if (!is_guest_mode(vcpu))
 		return 0;
 
+	/*
+	 * 32-bit SMRAM format doesn't preserve EFER and SVM state.  Userspace is
+	 * responsible for ensuring nested SVM and SMIs are mutually exclusive.
+	 */
+
+	if (!guest_cpuid_has(vcpu, X86_FEATURE_LM))
+		return 1;
+
 	smram->smram64.svm_guest_flag = 1;
 	smram->smram64.svm_guest_vmcb_gpa = svm->nested.vmcb12_gpa;
 
-- 
2.34.3