virt_linux: disable SMP for arm_v7 and change to tiny rcu

When SMP is enabled multicore specific instructions (e.g., pldw) are
generated. These are not supported and lead to invalid instruction
faults on uni-processor systems (like Cortex-A8). Therefore, we disable
SMP for arm_v7 in Linux code. This requires also a switch from the RCU
tree implementation to RCU tiny, which we shadow and dummy implemented.

issue #5104

repos/dde_linux/lib/import/import-lx_emul_common.inc

@@ -27,7 +27,6 @@ SRC_C   += lx_emul/shadow/kernel/irq_work.c
 SRC_C   += lx_emul/shadow/kernel/locking/spinlock.c
 SRC_C   += lx_emul/shadow/kernel/pid.c
 SRC_C   += lx_emul/shadow/kernel/printk/printk.c
-SRC_C   += lx_emul/shadow/kernel/rcu/tree.c
 SRC_C   += lx_emul/shadow/kernel/sched/cputime.c
 SRC_C   += lx_emul/shadow/kernel/sched/core.c
 SRC_C   += lx_emul/shadow/kernel/sched/fair.c
@@ -51,6 +50,13 @@ SRC_CC  += lx_kit/scheduler.cc
 SRC_CC  += lx_kit/task.cc
 SRC_CC  += lx_kit/timeout.cc
 
+# RCU for UP
+ifdef RCU_TINY
+SRC_C += lx_emul/shadow/kernel/rcu/tiny.c
+else
+SRC_C += lx_emul/shadow/kernel/rcu/tree.c
+endif
+
 ifeq ($(filter-out $(SPECS),x86_32),)
 LX_ARCH   := x86
 GEN_ARCH  := x86

repos/dde_linux/lib/import/import-virt_lx_emul.mk

@@ -21,7 +21,8 @@ ifeq ($(filter-out $(SPECS),arm_v6),)
 	INC_DIR += $(VIRT_LINUX_INCLUDE_DIR)/spec/arm_v6
 endif
 ifeq ($(filter-out $(SPECS),arm_v7),)
-	INC_DIR += $(VIRT_LINUX_INCLUDE_DIR)/spec/arm_v7
+	INC_DIR  += $(VIRT_LINUX_INCLUDE_DIR)/spec/arm_v7
+	RCU_TINY := yes
 endif
 ifeq ($(filter-out $(SPECS),arm_v8),)
 	INC_DIR += $(VIRT_LINUX_INCLUDE_DIR)/spec/arm_v8
@@ -30,13 +31,19 @@ endif
 -include $(call select_from_repositories,lib/import/import-lx_emul_common.inc)
 
 SRC_C  += lx_emul/shadow/drivers/char/random.c
-SRC_C  += lx_emul/shadow/kernel/rcu/srcutree.c
 SRC_C  += lx_emul/shadow/mm/page_alloc.c
 SRC_C  += lx_emul/shadow/mm/vmalloc.c
 SRC_C  += lx_emul/virt/common_dummies.c
 SRC_CC += lx_emul/virt/irq.cc
 SRC_CC += lx_kit/memory_non_dma.cc
 
+# RCU for UP
+ifdef RCU_TINY
+SRC_C += kernel/rcu/srcutiny.c
+else
+SRC_C += lx_emul/shadow/kernel/rcu/srcutree.c
+endif
+
 ifeq ($(filter-out $(SPECS),x86),)
 	SRC_C += lx_emul/virt/spec/x86/dummies_arch.c
 

repos/dde_linux/src/lib/lx_emul/shadow/kernel/rcu/tiny.c

@@ -0,0 +1,58 @@
+/*
+ * \brief  Replaces kernel/rcu/tiny.c for non-SMP
+ * \author Sebastian Sumpf
+ * \date   2024-02-01
+ */
+
+/*
+ * Copyright (C) 2024 Genode Labs GmbH
+ *
+ * This file is distributed under the terms of the GNU General Public License
+ * version 2.
+ */
+
+#include <linux/cache.h>
+#include <linux/types.h>
+#include <linux/time64.h> /* KTIME_MAX */
+#include <linux/mm.h>
+#include <linux/rcutiny.h>
+#include <linux/rcupdate.h>
+#include <linux/version.h>
+
+
+void call_rcu(struct rcu_head * head,
+              rcu_callback_t func)
+{
+	/*
+	 * In case func is a small offset kvfree should be
+	 * called directly, see 'rcu_reclaim_tiny'.
+	 */
+	enum { KVFREE_RCU_OFFSET = 4096, };
+	if (func < (rcu_callback_t)KVFREE_RCU_OFFSET) {
+		kvfree((void*)head - (unsigned long)func);
+		return;
+	}
+
+	func(head);
+}
+
+
+unsigned long get_state_synchronize_rcu(void)
+{
+	lx_emul_trace_and_stop(__func__);
+}
+
+
+unsigned long start_poll_synchronize_rcu(void)
+{
+	lx_emul_trace_and_stop(__func__);
+}
+
+
+bool poll_state_synchronize_rcu(unsigned long oldstate)
+{
+	lx_emul_trace_and_stop(__func__);
+}
+
+
+void rcu_qs(void) { }

repos/dde_linux/src/lib/lx_emul/virt/common_dummies.c

@@ -124,10 +124,12 @@ void ignore_signals(struct task_struct * t)
 	lx_emul_trace(__func__);
 }
 
+
+#ifdef CONFIG_TREE_SRCU
 #include <linux/srcu.h>
 
 void synchronize_srcu(struct srcu_struct * ssp)
 {
 	lx_emul_trace_and_stop(__func__);
 }
-
+#endif

repos/dde_linux/src/lib/virt_linux_generated/dep.list

@@ -793,6 +793,8 @@ include/linux/rcu_sync.h
 include/linux/rculist.h
 include/linux/rculist_bl.h
 include/linux/rcupdate.h
+include/linux/rcupdate_wait.h
+include/linux/rcutiny.h
 include/linux/rcutree.h
 include/linux/rcuwait.h
 include/linux/reboot.h
@@ -844,9 +846,13 @@ include/linux/smp_types.h
 include/linux/socket.h
 include/linux/spinlock.h
 include/linux/spinlock_api_smp.h
+include/linux/spinlock_api_up.h
 include/linux/spinlock_types.h
 include/linux/spinlock_types_raw.h
+include/linux/spinlock_types_up.h
+include/linux/spinlock_up.h
 include/linux/srcu.h
+include/linux/srcutiny.h
 include/linux/srcutree.h
 include/linux/stackdepot.h
 include/linux/stacktrace.h
@@ -908,6 +914,7 @@ include/linux/wait_bit.h
 include/linux/workqueue.h
 include/linux/writeback.h
 include/linux/xarray.h
+include/trace/events/rcu.h
 include/uapi/asm-generic/Kbuild
 include/uapi/asm-generic/bitsperlong.h
 include/uapi/asm-generic/errno-base.h
@@ -1022,6 +1029,9 @@ include/video/edid.h
 kernel/bounds.c
 kernel/configs/tiny-base.config
 kernel/configs/tiny.config
+kernel/rcu/rcu.h
+kernel/rcu/rcu_segcblist.h
+kernel/rcu/srcutiny.c
 kernel/time/timeconst.bc
 lib/ctype.c
 lib/gen_crc32table.c

repos/dde_linux/src/virt_linux/arm_v7/target.inc

@@ -5,3 +5,7 @@
 # do not generate thumb instructions on ARMv7 platforms
 LX_DISABLE += THUMB2_KERNEL ARM_VIRT_EXT DEBUG_PREEMPT
 
+# disable SMP because it will generate unsupported instruction on single core
+# Cortex-A8 CPUs
+LX_DISABLE += SMP
+