xen, pvh: fix unbootable VMs by inlining memset() in xen_prepare_pvh()

If this memset() is not inlined than PVH early boot code can call
into KASAN-instrumented memset() which results in unbootable VMs.
Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Acked-by: Juergen Gross <jgross@suse.com>
Message-ID: <20240802154253.482658-3-adobriyan@gmail.com>
Signed-off-by: Juergen Gross <jgross@suse.com>

arch/x86/platform/pvh/enlighten.c

@@ -130,7 +130,11 @@ void __init xen_prepare_pvh(void)
 		BUG();
 	}
 
-	memset(&pvh_bootparams, 0, sizeof(pvh_bootparams));
+	/*
+	 * This must not compile to "call memset" because memset() may be
+	 * instrumented.
+	 */
+	__builtin_memset(&pvh_bootparams, 0, sizeof(pvh_bootparams));
 
 	hypervisor_specific_init(xen_guest);