[PATCH v3 12/13] KVM: x86: SVM: don't save SVM state to SMRAM when VM is not long mode capable

From: Maxim Levitsky <mlevitsk@redhat.com>
To: kvm@vger.kernel.org
Cc: Borislav Petkov <bp@alien8.de>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	linux-kernel@vger.kernel.org, Wanpeng Li <wanpengli@tencent.com>,
	Maxim Levitsky <mlevitsk@redhat.com>,
	Ingo Molnar <mingo@redhat.com>,
	Sean Christopherson <seanjc@google.com>,
	x86@kernel.org, Jim Mattson <jmattson@google.com>,
	Kees Cook <keescook@chromium.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	"H. Peter Anvin" <hpa@zytor.com>, Joerg Roedel <joro@8bytes.org>,
	Vitaly Kuznetsov <vkuznets@redhat.com>,
	Paolo Bonzini <pbonzini@redhat.com>
Subject: [PATCH v3 12/13] KVM: x86: SVM: don't save SVM state to SMRAM when VM is not long mode capable
Date: Wed,  3 Aug 2022 18:50:10 +0300	[thread overview]
Message-ID: <20220803155011.43721-13-mlevitsk@redhat.com> (raw)
In-Reply-To: <20220803155011.43721-1-mlevitsk@redhat.com>

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 | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 7ca5e06878e19a..64cfd26bc5e7a6 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -4442,6 +4442,15 @@ 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.
+	 * SVM should not be enabled by the userspace without marking
+	 * the CPU as at least long mode capable.
+	 */
+
+	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;
 
-- 
2.26.3

