diff --git a/tools/testing/selftests/kvm/lib/x86_64/svm.c b/tools/testing/selftests/kvm/lib/x86_64/svm.c
index 2ac98d70d02bd..161eba7cd1289 100644
--- a/tools/testing/selftests/kvm/lib/x86_64/svm.c
+++ b/tools/testing/selftests/kvm/lib/x86_64/svm.c
@@ -54,6 +54,18 @@ static void vmcb_set_seg(struct vmcb_seg *seg, u16 selector,
 	seg->base = base;
 }
 
+/*
+ * Avoid using memset to clear the vmcb, since libc may not be
+ * available in L1 (and, even if it is, features that libc memset may
+ * want to use, like AVX, may not be enabled).
+ */
+static void clear_vmcb(struct vmcb *vmcb)
+{
+	int n = sizeof(*vmcb) / sizeof(u32);
+
+	asm volatile ("rep stosl" : "+c"(n), "+D"(vmcb) : "a"(0) : "memory");
+}
+
 void generic_svm_setup(struct svm_test_data *svm, void *guest_rip, void *guest_rsp)
 {
 	struct vmcb *vmcb = svm->vmcb;
@@ -70,7 +82,7 @@ void generic_svm_setup(struct svm_test_data *svm, void *guest_rip, void *guest_r
 	wrmsr(MSR_EFER, efer | EFER_SVME);
 	wrmsr(MSR_VM_HSAVE_PA, svm->save_area_gpa);
 
-	memset(vmcb, 0, sizeof(*vmcb));
+	clear_vmcb(vmcb);
 	asm volatile ("vmsave %0\n\t" : : "a" (vmcb_gpa) : "memory");
 	vmcb_set_seg(&save->es, get_es(), 0, -1U, data_seg_attr);
 	vmcb_set_seg(&save->cs, get_cs(), 0, -1U, code_seg_attr);