On Thu, Nov 18, 2021 at 05:00:58PM +0100, Peter Zijlstra wrote:

> Dear um folks, is this indeed the best solution? It's a bit sad to have
> to add this to x86_64, but if that's the way it is...

Something like this, perhaps? (absolutely untested)

diff --git a/arch/um/include/asm/Kbuild b/arch/um/include/asm/Kbuild
index e5a7b552bb384..a58b67ec8119d 100644
--- a/arch/um/include/asm/Kbuild
+++ b/arch/um/include/asm/Kbuild
@@ -23,7 +23,6 @@ generic-y += softirq_stack.h
 generic-y += switch_to.h
 generic-y += topology.h
 generic-y += trace_clock.h
-generic-y += word-at-a-time.h
 generic-y += kprobes.h
 generic-y += mm_hooks.h
 generic-y += vga.h
diff --git a/arch/x86/um/Kconfig b/arch/x86/um/Kconfig
index 95d26a69088b1..a812cc35092c6 100644
--- a/arch/x86/um/Kconfig
+++ b/arch/x86/um/Kconfig
@@ -9,6 +9,7 @@ endmenu
 config UML_X86
 	def_bool y
 	select GENERIC_FIND_FIRST_BIT
+	select DCACHE_WORD_ACCESS
 
 config 64BIT
 	bool "64-bit kernel" if "$(SUBARCH)" = "x86"