diff --git a/arch/um/Kconfig b/arch/um/Kconfig
index 1d4def0db841..49781bee7905 100644
--- a/arch/um/Kconfig
+++ b/arch/um/Kconfig
@@ -39,6 +39,7 @@ config UML
 	select HAVE_ARCH_TRACEHOOK
 	select HAVE_SYSCALL_TRACEPOINTS
 	select THREAD_INFO_IN_TASK
+	select SPARSE_IRQ
 
 config MMU
 	bool
diff --git a/arch/um/drivers/ssl.c b/arch/um/drivers/ssl.c
index 277cea3d30eb..8006a5bd578c 100644
--- a/arch/um/drivers/ssl.c
+++ b/arch/um/drivers/ssl.c
@@ -199,4 +199,7 @@ static int ssl_non_raw_setup(char *str)
 	return 1;
 }
 __setup("ssl-non-raw", ssl_non_raw_setup);
-__channel_help(ssl_non_raw_setup, "set serial lines to non-raw mode");
+__uml_help(ssl_non_raw_setup,
+"ssl-non-raw\n"
+"    Set serial lines to non-raw mode.\n\n"
+);
diff --git a/arch/um/drivers/ubd_kern.c b/arch/um/drivers/ubd_kern.c
index f2b2feeeb455..37455e74d314 100644
--- a/arch/um/drivers/ubd_kern.c
+++ b/arch/um/drivers/ubd_kern.c
@@ -370,7 +370,7 @@ __uml_help(ubd_setup,
 "    useful when a unique number should be given to the device. Note when\n"
 "    specifying a label, the filename2 must be also presented. It can be\n"
 "    an empty string, in which case the backing file is not used:\n"
-"       ubd0=File,,Serial\n"
+"       ubd0=File,,Serial\n\n"
 );
 
 static int udb_setup(char *str)
diff --git a/arch/um/drivers/vector_kern.c b/arch/um/drivers/vector_kern.c
index 9bbbddfe866b..25d9258fa592 100644
--- a/arch/um/drivers/vector_kern.c
+++ b/arch/um/drivers/vector_kern.c
@@ -1721,7 +1721,7 @@ static int __init vector_setup(char *str)
 __setup("vec", vector_setup);
 __uml_help(vector_setup,
 "vec[0-9]+:<option>=<value>,<option>=<value>\n"
-"	 Configure a vector io network device.\n\n"
+"    Configure a vector io network device.\n\n"
 );
 
 late_initcall(vector_init);
diff --git a/arch/um/drivers/virtio_pcidev.c b/arch/um/drivers/virtio_pcidev.c
index e9e23cc3f357..f9b4b6f7582c 100644
--- a/arch/um/drivers/virtio_pcidev.c
+++ b/arch/um/drivers/virtio_pcidev.c
@@ -598,6 +598,11 @@ static void virtio_pcidev_virtio_remove(struct virtio_device *vdev)
 	kfree(dev);
 }
 
+static void virtio_pcidev_virtio_shutdown(struct virtio_device *vdev)
+{
+	/* nothing to do, we just don't want queue shutdown */
+}
+
 static struct virtio_device_id id_table[] = {
 	{ CONFIG_UML_PCI_OVER_VIRTIO_DEVICE_ID, VIRTIO_DEV_ANY_ID },
 	{ 0 },
@@ -609,6 +614,7 @@ static struct virtio_driver virtio_pcidev_virtio_driver = {
 	.id_table = id_table,
 	.probe = virtio_pcidev_virtio_probe,
 	.remove = virtio_pcidev_virtio_remove,
+	.shutdown = virtio_pcidev_virtio_shutdown,
 };
 
 static int __init virtio_pcidev_init(void)
diff --git a/arch/um/include/asm/mmu_context.h b/arch/um/include/asm/mmu_context.h
index 0bbb24868557..c727e56ba116 100644
--- a/arch/um/include/asm/mmu_context.h
+++ b/arch/um/include/asm/mmu_context.h
@@ -13,20 +13,9 @@
 #include <asm/mm_hooks.h>
 #include <asm/mmu.h>
 
-#define activate_mm activate_mm
-static inline void activate_mm(struct mm_struct *old, struct mm_struct *new)
-{
-}
-
 static inline void switch_mm(struct mm_struct *prev, struct mm_struct *next, 
 			     struct task_struct *tsk)
 {
-	unsigned cpu = smp_processor_id();
-
-	if (prev != next) {
-		cpumask_clear_cpu(cpu, mm_cpumask(prev));
-		cpumask_set_cpu(cpu, mm_cpumask(next));
-	}
 }
 
 #define init_new_context init_new_context
diff --git a/arch/um/include/asm/processor-generic.h b/arch/um/include/asm/processor-generic.h
index 8a789c17acd8..7854d51b6639 100644
--- a/arch/um/include/asm/processor-generic.h
+++ b/arch/um/include/asm/processor-generic.h
@@ -71,7 +71,6 @@ extern void start_thread(struct pt_regs *regs, unsigned long entry,
 
 struct cpuinfo_um {
 	unsigned long loops_per_jiffy;
-	int ipi_pipe[2];
 	int cache_alignment;
 	union {
 		__u32		x86_capability[NCAPINTS + NBUGINTS];
@@ -81,8 +80,6 @@ struct cpuinfo_um {
 
 extern struct cpuinfo_um boot_cpu_data;
 
-#define cpu_data(cpu)    boot_cpu_data
-#define current_cpu_data boot_cpu_data
 #define cache_line_size()	(boot_cpu_data.cache_alignment)
 
 #define KSTK_REG(tsk, reg) get_thread_reg(reg, &tsk->thread.switch_buf)
diff --git a/arch/um/include/shared/as-layout.h b/arch/um/include/shared/as-layout.h
index 2f9bfd99460a..7c7e17bce403 100644
--- a/arch/um/include/shared/as-layout.h
+++ b/arch/um/include/shared/as-layout.h
@@ -23,8 +23,9 @@
 #define STUB_START stub_start
 #define STUB_CODE STUB_START
 #define STUB_DATA (STUB_CODE + UM_KERN_PAGE_SIZE)
-#define STUB_DATA_PAGES 2 /* must be a power of two */
-#define STUB_END (STUB_DATA + STUB_DATA_PAGES * UM_KERN_PAGE_SIZE)
+#define STUB_DATA_PAGES 2
+#define STUB_SIZE ((1 + STUB_DATA_PAGES) * UM_KERN_PAGE_SIZE)
+#define STUB_END (STUB_START + STUB_SIZE)
 
 #ifndef __ASSEMBLER__
 
diff --git a/arch/um/include/shared/skas/stub-data.h b/arch/um/include/shared/skas/stub-data.h
index c261a77a32f6..27db38e95df9 100644
--- a/arch/um/include/shared/skas/stub-data.h
+++ b/arch/um/include/shared/skas/stub-data.h
@@ -53,8 +53,7 @@ struct stub_syscall {
 };
 
 struct stub_data {
-	unsigned long offset;
-	long err, child_err;
+	long err;
 
 	int syscall_data_len;
 	/* 128 leaves enough room for additional fields in the struct */
diff --git a/arch/um/kernel/dtb.c b/arch/um/kernel/dtb.c
index 15c342426489..47cd3d869fb2 100644
--- a/arch/um/kernel/dtb.c
+++ b/arch/um/kernel/dtb.c
@@ -38,5 +38,5 @@ static int __init uml_dtb_setup(char *line, int *add)
 
 __uml_setup("dtb=", uml_dtb_setup,
 "dtb=<file>\n"
-"    Boot the kernel with the devicetree blob from the specified file.\n"
+"    Boot the kernel with the devicetree blob from the specified file.\n\n"
 );
diff --git a/arch/um/kernel/irq.c b/arch/um/kernel/irq.c
index 0dfaf96bb7da..d69d137a0334 100644
--- a/arch/um/kernel/irq.c
+++ b/arch/um/kernel/irq.c
@@ -691,6 +691,11 @@ void __init init_IRQ(void)
 	os_setup_epoll();
 }
 
+int __init arch_probe_nr_irqs(void)
+{
+	return NR_IRQS;
+}
+
 void sigchld_handler(int sig, struct siginfo *unused_si,
 		     struct uml_pt_regs *regs, void *mc)
 {
diff --git a/arch/um/kernel/time.c b/arch/um/kernel/time.c
index ae0fa2173778..17da0a870650 100644
--- a/arch/um/kernel/time.c
+++ b/arch/um/kernel/time.c
@@ -986,26 +986,26 @@ static int setup_time_travel(char *str)
 __setup("time-travel", setup_time_travel);
 __uml_help(setup_time_travel,
 "time-travel\n"
-"This option just enables basic time travel mode, in which the clock/timers\n"
-"inside the UML instance skip forward when there's nothing to do, rather than\n"
-"waiting for real time to elapse. However, instance CPU speed is limited by\n"
-"the real CPU speed, so e.g. a 10ms timer will always fire after ~10ms wall\n"
-"clock (but quicker when there's nothing to do).\n"
+"    This option just enables basic time travel mode, in which the clock/timers\n"
+"    inside the UML instance skip forward when there's nothing to do, rather than\n"
+"    waiting for real time to elapse. However, instance CPU speed is limited by\n"
+"    the real CPU speed, so e.g. a 10ms timer will always fire after ~10ms wall\n"
+"    clock (but quicker when there's nothing to do).\n"
 "\n"
 "time-travel=inf-cpu\n"
-"This enables time travel mode with infinite processing power, in which there\n"
-"are no wall clock timers, and any CPU processing happens - as seen from the\n"
-"guest - instantly. This can be useful for accurate simulation regardless of\n"
-"debug overhead, physical CPU speed, etc. but is somewhat dangerous as it can\n"
-"easily lead to getting stuck (e.g. if anything in the system busy loops).\n"
+"    This enables time travel mode with infinite processing power, in which there\n"
+"    are no wall clock timers, and any CPU processing happens - as seen from the\n"
+"    guest - instantly. This can be useful for accurate simulation regardless of\n"
+"    debug overhead, physical CPU speed, etc. but is somewhat dangerous as it can\n"
+"    easily lead to getting stuck (e.g. if anything in the system busy loops).\n"
 "\n"
 "time-travel=ext:[ID:]/path/to/socket\n"
-"This enables time travel mode similar to =inf-cpu, except the system will\n"
-"use the given socket to coordinate with a central scheduler, in order to\n"
-"have more than one system simultaneously be on simulated time. The virtio\n"
-"driver code in UML knows about this so you can also simulate networks and\n"
-"devices using it, assuming the device has the right capabilities.\n"
-"The optional ID is a 64-bit integer that's sent to the central scheduler.\n");
+"    This enables time travel mode similar to =inf-cpu, except the system will\n"
+"    use the given socket to coordinate with a central scheduler, in order to\n"
+"    have more than one system simultaneously be on simulated time. The virtio\n"
+"    driver code in UML knows about this so you can also simulate networks and\n"
+"    devices using it, assuming the device has the right capabilities.\n"
+"    The optional ID is a 64-bit integer that's sent to the central scheduler.\n\n");
 
 static int setup_time_travel_start(char *str)
 {
@@ -1022,8 +1022,9 @@ static int setup_time_travel_start(char *str)
 __setup("time-travel-start=", setup_time_travel_start);
 __uml_help(setup_time_travel_start,
 "time-travel-start=<nanoseconds>\n"
-"Configure the UML instance's wall clock to start at this value rather than\n"
-"the host's wall clock at the time of UML boot.\n");
+"    Configure the UML instance's wall clock to start at this value rather than\n"
+"    the host's wall clock at the time of UML boot.\n\n");
+
 static struct kobject *bc_time_kobject;
 
 static ssize_t bc_show(struct kobject *kobj, struct kobj_attribute *attr, char *buf)
diff --git a/arch/um/kernel/um_arch.c b/arch/um/kernel/um_arch.c
index 2f5ee045bc7a..cfbbbf8500c3 100644
--- a/arch/um/kernel/um_arch.c
+++ b/arch/um/kernel/um_arch.c
@@ -54,12 +54,9 @@ static void __init add_arg(char *arg)
 
 /*
  * These fields are initialized at boot time and not changed.
- * XXX This structure is used only in the non-SMP case.  Maybe this
- * should be moved to smp.c.
  */
 struct cpuinfo_um boot_cpu_data = {
 	.loops_per_jiffy	= 0,
-	.ipi_pipe		= { -1, -1 },
 	.cache_alignment	= L1_CACHE_BYTES,
 	.x86_capability		= { 0 }
 };
@@ -331,9 +328,7 @@ int __init linux_main(int argc, char **argv, char **envp)
 
 	host_task_size = get_top_address(envp);
 	/* reserve a few pages for the stubs */
-	stub_start = host_task_size - STUB_DATA_PAGES * PAGE_SIZE;
-	/* another page for the code portion */
-	stub_start -= PAGE_SIZE;
+	stub_start = host_task_size - STUB_SIZE;
 	host_task_size = stub_start;
 
 	/* Limit TASK_SIZE to what is addressable by the page table */
diff --git a/arch/um/os-Linux/skas/process.c b/arch/um/os-Linux/skas/process.c
index 78f48fa9db8b..0bc10cd4cbed 100644
--- a/arch/um/os-Linux/skas/process.c
+++ b/arch/um/os-Linux/skas/process.c
@@ -895,7 +895,7 @@ __uml_setup("noreboot", noreboot_cmd_param,
 "noreboot\n"
 "    Rather than rebooting, exit always, akin to QEMU's -no-reboot option.\n"
 "    This is useful if you're using CONFIG_PANIC_TIMEOUT in order to catch\n"
-"    crashes in CI\n");
+"    crashes in CI\n\n");
 
 void reboot_skas(void)
 {
diff --git a/arch/x86/um/shared/sysdep/stub_32.h b/arch/x86/um/shared/sysdep/stub_32.h
index df568fc3ceb4..9dc2efaf5df1 100644
--- a/arch/x86/um/shared/sysdep/stub_32.h
+++ b/arch/x86/um/shared/sysdep/stub_32.h
@@ -129,7 +129,7 @@ static __always_inline void *get_stub_data(void)
 		"subl %0,%%esp ;"					\
 		"movl %1, %%eax ; "					\
 		"call *%%eax ;"						\
-		:: "i" ((1 + STUB_DATA_PAGES) * UM_KERN_PAGE_SIZE),	\
+		:: "i" (STUB_SIZE),					\
 		   "i" (&fn))
 
 static __always_inline void
diff --git a/arch/x86/um/shared/sysdep/stub_64.h b/arch/x86/um/shared/sysdep/stub_64.h
index 9cfd31afa769..9fd56954e2e0 100644
--- a/arch/x86/um/shared/sysdep/stub_64.h
+++ b/arch/x86/um/shared/sysdep/stub_64.h
@@ -133,7 +133,7 @@ static __always_inline void *get_stub_data(void)
 		"subq %0,%%rsp ;"					\
 		"movq %1,%%rax ;"					\
 		"call *%%rax ;"						\
-		:: "i" ((1 + STUB_DATA_PAGES) * UM_KERN_PAGE_SIZE),	\
+		:: "i" (STUB_SIZE),					\
 		   "i" (&fn))
 
 static __always_inline void