um: Fix time-travel=inf-cpu with xor/raid6

Today, I erroneously built a time-travel configuration with btrfs
enabled, and noticed it cannot boot in time-travel=inf-cpu mode,
both xor and raid6 speed measurement gets stuck.

For xor, work around it by picking the first algorithm if inf-cpu
mode is enabled.

For raid6, I didn't find such a workaround, so disallow enabling
time-travel mode if RAID6_PQ_BENCHMARK is enabled.

With this, and RAID6_PQ_BENCHMARK disabled, I can boot a kernel
that has btrfs enabled in time-travel=inf-cpu mode.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Acked-by: Anton Ivanov <anton.ivanov@cambridgegreys.com>
Signed-off-by: Richard Weinberger <richard@nod.at>

arch/um/Kconfig

@@ -189,6 +189,8 @@ config SECCOMP
 config UML_TIME_TRAVEL_SUPPORT
 	bool
 	prompt "Support time-travel mode (e.g. for test execution)"
+	# inf-cpu mode is incompatible with the benchmarking
+	depends on !RAID6_PQ_BENCHMARK
 	help
 	  Enable this option to support time travel inside the UML instance.
 

arch/um/include/asm/Kbuild

@@ -25,5 +25,4 @@ generic-y += switch_to.h
 generic-y += topology.h
 generic-y += trace_clock.h
 generic-y += word-at-a-time.h
-generic-y += xor.h
 generic-y += kprobes.h

arch/um/include/asm/xor.h

@@ -0,0 +1,7 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#include <asm-generic/xor.h>
+#include <shared/timer-internal.h>
+
+/* pick an arbitrary one - measuring isn't possible with inf-cpu */
+#define XOR_SELECT_TEMPLATE(x)	\
+	(time_travel_mode == TT_MODE_INFCPU ? &xor_block_8regs : NULL)