diff -Naur linux-5.9.orig/tools/perf/Documentation/Makefile linux-5.9/tools/perf/Documentation/Makefile
--- linux-5.9.orig/tools/perf/Documentation/Makefile	2020-10-17 12:00:45.497122395 +0300
+++ linux-5.9/tools/perf/Documentation/Makefile	2020-10-17 12:00:47.205122425 +0300
@@ -51,7 +51,7 @@
 ASCIIDOC_EXTRA += --unsafe -f asciidoc.conf
 ASCIIDOC_HTML = xhtml11
 MANPAGE_XSL = manpage-normal.xsl
-XMLTO_EXTRA =
+XMLTO_EXTRA = --skip-validation
 INSTALL?=install
 RM ?= rm -f
 DOC_REF = origin/man