[PATCH v4 2/3] KVM: SEV-ES: Disallow SEV-ES guests when X86_FEATURE_LBRV is absent

[Ravi Bangoria <ravi.bangoria@amd.com>]

As documented in APM[1], LBR Virtualization must be enabled for SEV-ES
guests. So, prevent SEV-ES guests when LBRV support is missing.

[1]: AMD64 Architecture Programmer's Manual Pub. 40332, Rev. 4.07 - June
     2023, Vol 2, 15.35.2 Enabling SEV-ES.
     https://bugzilla.kernel.org/attachment.cgi?id=304653

Fixes: 376c6d285017 ("KVM: SVM: Provide support for SEV-ES vCPU creation/loading")
Signed-off-by: Ravi Bangoria <ravi.bangoria@amd.com>
---
 arch/x86/kvm/svm/sev.c |  6 ++++++
 arch/x86/kvm/svm/svm.c | 16 +++++++---------
 arch/x86/kvm/svm/svm.h |  1 +
 3 files changed, 14 insertions(+), 9 deletions(-)

diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index 176ba117413a..8345a5098ab7 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -2933,6 +2933,12 @@ void __init sev_hardware_setup(void)
 	if (!boot_cpu_has(X86_FEATURE_SEV_ES))
 		goto out;
 
+	if (!lbrv) {
+		WARN_ONCE(!boot_cpu_has(X86_FEATURE_LBRV),
+			  "LBRV must be present for SEV-ES support");
+		goto out;
+	}
+
 	/* Has the system been allocated ASIDs for SEV-ES? */
 	if (min_sev_asid == 1)
 		goto out;
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 1a01293f6909..cadf3085f183 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -215,7 +215,7 @@ int vgif = true;
 module_param(vgif, int, 0444);
 
 /* enable/disable LBR virtualization */
-static int lbrv = true;
+int lbrv = true;
 module_param(lbrv, int, 0444);
 
 static int tsc_scaling = true;
@@ -5308,6 +5308,12 @@ static __init int svm_hardware_setup(void)
 
 	nrips = nrips && boot_cpu_has(X86_FEATURE_NRIPS);
 
+	if (lbrv) {
+		if (!boot_cpu_has(X86_FEATURE_LBRV))
+			lbrv = false;
+		else
+			pr_info("LBR virtualization supported\n");
+	}
 	/*
 	 * Note, SEV setup consumes npt_enabled and enable_mmio_caching (which
 	 * may be modified by svm_adjust_mmio_mask()), as well as nrips.
@@ -5361,14 +5367,6 @@ static __init int svm_hardware_setup(void)
 		svm_x86_ops.set_vnmi_pending = NULL;
 	}
 
-
-	if (lbrv) {
-		if (!boot_cpu_has(X86_FEATURE_LBRV))
-			lbrv = false;
-		else
-			pr_info("LBR virtualization supported\n");
-	}
-
 	if (!enable_pmu)
 		pr_info("PMU virtualization is disabled\n");
 
diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
index 555c55f50298..2d6c19c55b1a 100644
--- a/arch/x86/kvm/svm/svm.h
+++ b/arch/x86/kvm/svm/svm.h
@@ -39,6 +39,7 @@ extern int vgif;
 extern bool intercept_smi;
 extern bool x2avic_enabled;
 extern bool vnmi;
+extern int lbrv;
 
 /*
  * Clean bits in VMCB.
-- 
2.45.1