1// SPDX-License-Identifier: GPL-2.0
2/*
3 * Xen SMP support
4 *
5 * This file implements the Xen versions of smp_ops. SMP under Xen is
6 * very straightforward. Bringing a CPU up is simply a matter of
7 * loading its initial context and setting it running.
8 *
9 * IPIs are handled through the Xen event mechanism.
10 *
11 * Because virtual CPUs can be scheduled onto any real CPU, there's no
12 * useful topology information for the kernel to make use of. As a
13 * result, all CPUs are treated as if they're single-core and
14 * single-threaded.
15 */
16#include <linux/sched.h>
17#include <linux/sched/task_stack.h>
18#include <linux/err.h>
19#include <linux/slab.h>
20#include <linux/smp.h>
21#include <linux/irq_work.h>
22#include <linux/tick.h>
23#include <linux/nmi.h>
24#include <linux/cpuhotplug.h>
25#include <linux/stackprotector.h>
26#include <linux/pgtable.h>
27
28#include <asm/paravirt.h>
29#include <asm/idtentry.h>
30#include <asm/desc.h>
31#include <asm/cpu.h>
32#include <asm/io_apic.h>
33
34#include <xen/interface/xen.h>
35#include <xen/interface/vcpu.h>
36#include <xen/interface/xenpmu.h>
37
38#include <asm/spec-ctrl.h>
39#include <asm/xen/interface.h>
40#include <asm/xen/hypercall.h>
41
42#include <xen/xen.h>
43#include <xen/page.h>
44#include <xen/events.h>
45
46#include <xen/hvc-console.h>
47#include "xen-ops.h"
48#include "mmu.h"
49#include "smp.h"
50#include "pmu.h"
51
52cpumask_var_t xen_cpu_initialized_map;
53
54static DEFINE_PER_CPU(struct xen_common_irq, xen_irq_work) = { .irq = -1 };
55static DEFINE_PER_CPU(struct xen_common_irq, xen_pmu_irq) = { .irq = -1 };
56
57static irqreturn_t xen_irq_work_interrupt(int irq, void *dev_id);
58
59static void cpu_bringup(void)
60{
61 int cpu;
62
63 cr4_init();
64 cpuhp_ap_sync_alive();
65 cpu_init();
66 fpu__init_cpu();
67 touch_softlockup_watchdog();
68
69 /* PVH runs in ring 0 and allows us to do native syscalls. Yay! */
70 if (!xen_feature(XENFEAT_supervisor_mode_kernel)) {
71 xen_enable_sysenter();
72 xen_enable_syscall();
73 }
74 cpu = smp_processor_id();
75 smp_store_cpu_info(id: cpu);
76 cpu_data(cpu).x86_max_cores = 1;
77 set_cpu_sibling_map(cpu);
78
79 speculative_store_bypass_ht_init();
80
81 xen_setup_cpu_clockevents();
82
83 notify_cpu_starting(cpu);
84
85 set_cpu_online(cpu, online: true);
86
87 smp_mb();
88
89 /* We can take interrupts now: we're officially "up". */
90 local_irq_enable();
91}
92
93asmlinkage __visible void cpu_bringup_and_idle(void)
94{
95 cpu_bringup();
96 cpu_startup_entry(state: CPUHP_AP_ONLINE_IDLE);
97}
98
99void xen_smp_intr_free_pv(unsigned int cpu)
100{
101 kfree(per_cpu(xen_irq_work, cpu).name);
102 per_cpu(xen_irq_work, cpu).name = NULL;
103 if (per_cpu(xen_irq_work, cpu).irq >= 0) {
104 unbind_from_irqhandler(per_cpu(xen_irq_work, cpu).irq, NULL);
105 per_cpu(xen_irq_work, cpu).irq = -1;
106 }
107
108 kfree(per_cpu(xen_pmu_irq, cpu).name);
109 per_cpu(xen_pmu_irq, cpu).name = NULL;
110 if (per_cpu(xen_pmu_irq, cpu).irq >= 0) {
111 unbind_from_irqhandler(per_cpu(xen_pmu_irq, cpu).irq, NULL);
112 per_cpu(xen_pmu_irq, cpu).irq = -1;
113 }
114}
115
116int xen_smp_intr_init_pv(unsigned int cpu)
117{
118 int rc;
119 char *callfunc_name, *pmu_name;
120
121 callfunc_name = kasprintf(GFP_KERNEL, fmt: "irqwork%d", cpu);
122 per_cpu(xen_irq_work, cpu).name = callfunc_name;
123 rc = bind_ipi_to_irqhandler(ipi: XEN_IRQ_WORK_VECTOR,
124 cpu,
125 handler: xen_irq_work_interrupt,
126 IRQF_PERCPU|IRQF_NOBALANCING,
127 devname: callfunc_name,
128 NULL);
129 if (rc < 0)
130 goto fail;
131 per_cpu(xen_irq_work, cpu).irq = rc;
132
133 if (is_xen_pmu) {
134 pmu_name = kasprintf(GFP_KERNEL, fmt: "pmu%d", cpu);
135 per_cpu(xen_pmu_irq, cpu).name = pmu_name;
136 rc = bind_virq_to_irqhandler(VIRQ_XENPMU, cpu,
137 handler: xen_pmu_irq_handler,
138 IRQF_PERCPU|IRQF_NOBALANCING,
139 devname: pmu_name, NULL);
140 if (rc < 0)
141 goto fail;
142 per_cpu(xen_pmu_irq, cpu).irq = rc;
143 }
144
145 return 0;
146
147 fail:
148 xen_smp_intr_free_pv(cpu);
149 return rc;
150}
151
152static void __init _get_smp_config(unsigned int early)
153{
154 int i, rc;
155 unsigned int subtract = 0;
156
157 if (early)
158 return;
159
160 num_processors = 0;
161 disabled_cpus = 0;
162 for (i = 0; i < nr_cpu_ids; i++) {
163 rc = HYPERVISOR_vcpu_op(VCPUOP_is_up, vcpuid: i, NULL);
164 if (rc >= 0) {
165 num_processors++;
166 set_cpu_possible(cpu: i, possible: true);
167 } else {
168 set_cpu_possible(cpu: i, possible: false);
169 set_cpu_present(cpu: i, present: false);
170 subtract++;
171 }
172 }
173#ifdef CONFIG_HOTPLUG_CPU
174 /* This is akin to using 'nr_cpus' on the Linux command line.
175 * Which is OK as when we use 'dom0_max_vcpus=X' we can only
176 * have up to X, while nr_cpu_ids is greater than X. This
177 * normally is not a problem, except when CPU hotplugging
178 * is involved and then there might be more than X CPUs
179 * in the guest - which will not work as there is no
180 * hypercall to expand the max number of VCPUs an already
181 * running guest has. So cap it up to X. */
182 if (subtract)
183 set_nr_cpu_ids(nr_cpu_ids - subtract);
184#endif
185 /* Pretend to be a proper enumerated system */
186 smp_found_config = 1;
187}
188
189static void __init xen_pv_smp_prepare_boot_cpu(void)
190{
191 BUG_ON(smp_processor_id() != 0);
192 native_smp_prepare_boot_cpu();
193
194 if (!xen_feature(XENFEAT_writable_page_tables))
195 /* We've switched to the "real" per-cpu gdt, so make
196 * sure the old memory can be recycled. */
197 make_lowmem_page_readwrite(vaddr: xen_initial_gdt);
198
199 xen_setup_vcpu_info_placement();
200
201 /*
202 * The alternative logic (which patches the unlock/lock) runs before
203 * the smp bootup up code is activated. Hence we need to set this up
204 * the core kernel is being patched. Otherwise we will have only
205 * modules patched but not core code.
206 */
207 xen_init_spinlocks();
208}
209
210static void __init xen_pv_smp_prepare_cpus(unsigned int max_cpus)
211{
212 unsigned cpu;
213
214 if (ioapic_is_disabled) {
215 char *m = (max_cpus == 0) ?
216 "The nosmp parameter is incompatible with Xen; " \
217 "use Xen dom0_max_vcpus=1 parameter" :
218 "The noapic parameter is incompatible with Xen";
219
220 xen_raw_printk(fmt: m);
221 panic(fmt: m);
222 }
223 xen_init_lock_cpu(cpu: 0);
224
225 smp_prepare_cpus_common();
226
227 cpu_data(0).x86_max_cores = 1;
228
229 speculative_store_bypass_ht_init();
230
231 xen_pmu_init(cpu: 0);
232
233 if (xen_smp_intr_init(cpu: 0) || xen_smp_intr_init_pv(cpu: 0))
234 BUG();
235
236 if (!alloc_cpumask_var(mask: &xen_cpu_initialized_map, GFP_KERNEL))
237 panic(fmt: "could not allocate xen_cpu_initialized_map\n");
238
239 cpumask_copy(dstp: xen_cpu_initialized_map, cpumask_of(0));
240
241 /* Restrict the possible_map according to max_cpus. */
242 while ((num_possible_cpus() > 1) && (num_possible_cpus() > max_cpus)) {
243 for (cpu = nr_cpu_ids - 1; !cpu_possible(cpu); cpu--)
244 continue;
245 set_cpu_possible(cpu, possible: false);
246 }
247
248 for_each_possible_cpu(cpu)
249 set_cpu_present(cpu, present: true);
250}
251
252static int
253cpu_initialize_context(unsigned int cpu, struct task_struct *idle)
254{
255 struct vcpu_guest_context *ctxt;
256 struct desc_struct *gdt;
257 unsigned long gdt_mfn;
258
259 if (cpumask_test_and_set_cpu(cpu, cpumask: xen_cpu_initialized_map))
260 return 0;
261
262 ctxt = kzalloc(size: sizeof(*ctxt), GFP_KERNEL);
263 if (ctxt == NULL) {
264 cpumask_clear_cpu(cpu, dstp: xen_cpu_initialized_map);
265 return -ENOMEM;
266 }
267
268 gdt = get_cpu_gdt_rw(cpu);
269
270 /*
271 * Bring up the CPU in cpu_bringup_and_idle() with the stack
272 * pointing just below where pt_regs would be if it were a normal
273 * kernel entry.
274 */
275 ctxt->user_regs.eip = (unsigned long)asm_cpu_bringup_and_idle;
276 ctxt->flags = VGCF_IN_KERNEL;
277 ctxt->user_regs.eflags = 0x1000; /* IOPL_RING1 */
278 ctxt->user_regs.ds = __USER_DS;
279 ctxt->user_regs.es = __USER_DS;
280 ctxt->user_regs.ss = __KERNEL_DS;
281 ctxt->user_regs.cs = __KERNEL_CS;
282 ctxt->user_regs.esp = (unsigned long)task_pt_regs(idle);
283
284 xen_copy_trap_info(traps: ctxt->trap_ctxt);
285
286 BUG_ON((unsigned long)gdt & ~PAGE_MASK);
287
288 gdt_mfn = arbitrary_virt_to_mfn(vaddr: gdt);
289 make_lowmem_page_readonly(vaddr: gdt);
290 make_lowmem_page_readonly(mfn_to_virt(gdt_mfn));
291
292 ctxt->gdt_frames[0] = gdt_mfn;
293 ctxt->gdt_ents = GDT_ENTRIES;
294
295 /*
296 * Set SS:SP that Xen will use when entering guest kernel mode
297 * from guest user mode. Subsequent calls to load_sp0() can
298 * change this value.
299 */
300 ctxt->kernel_ss = __KERNEL_DS;
301 ctxt->kernel_sp = task_top_of_stack(idle);
302
303 ctxt->gs_base_kernel = per_cpu_offset(cpu);
304 ctxt->event_callback_eip =
305 (unsigned long)xen_asm_exc_xen_hypervisor_callback;
306 ctxt->failsafe_callback_eip =
307 (unsigned long)xen_failsafe_callback;
308 per_cpu(xen_cr3, cpu) = __pa(swapper_pg_dir);
309
310 ctxt->ctrlreg[3] = xen_pfn_to_cr3(virt_to_gfn(swapper_pg_dir));
311 if (HYPERVISOR_vcpu_op(VCPUOP_initialise, vcpuid: xen_vcpu_nr(cpu), extra_args: ctxt))
312 BUG();
313
314 kfree(objp: ctxt);
315 return 0;
316}
317
318static int xen_pv_kick_ap(unsigned int cpu, struct task_struct *idle)
319{
320 int rc;
321
322 rc = common_cpu_up(cpunum: cpu, tidle: idle);
323 if (rc)
324 return rc;
325
326 xen_setup_runstate_info(cpu);
327
328 /* make sure interrupts start blocked */
329 per_cpu(xen_vcpu, cpu)->evtchn_upcall_mask = 1;
330
331 rc = cpu_initialize_context(cpu, idle);
332 if (rc)
333 return rc;
334
335 xen_pmu_init(cpu);
336
337 /*
338 * Why is this a BUG? If the hypercall fails then everything can be
339 * rolled back, no?
340 */
341 BUG_ON(HYPERVISOR_vcpu_op(VCPUOP_up, xen_vcpu_nr(cpu), NULL));
342
343 return 0;
344}
345
346static void xen_pv_poll_sync_state(void)
347{
348 HYPERVISOR_sched_op(SCHEDOP_yield, NULL);
349}
350
351#ifdef CONFIG_HOTPLUG_CPU
352static int xen_pv_cpu_disable(void)
353{
354 unsigned int cpu = smp_processor_id();
355 if (cpu == 0)
356 return -EBUSY;
357
358 cpu_disable_common();
359
360 load_cr3(swapper_pg_dir);
361 return 0;
362}
363
364static void xen_pv_cpu_die(unsigned int cpu)
365{
366 while (HYPERVISOR_vcpu_op(VCPUOP_is_up, vcpuid: xen_vcpu_nr(cpu), NULL)) {
367 __set_current_state(TASK_UNINTERRUPTIBLE);
368 schedule_timeout(HZ/10);
369 }
370}
371
372static void xen_pv_cleanup_dead_cpu(unsigned int cpu)
373{
374 xen_smp_intr_free(cpu);
375 xen_uninit_lock_cpu(cpu);
376 xen_teardown_timer(cpu);
377 xen_pmu_finish(cpu);
378}
379
380static void __noreturn xen_pv_play_dead(void) /* used only with HOTPLUG_CPU */
381{
382 play_dead_common();
383 HYPERVISOR_vcpu_op(VCPUOP_down, vcpuid: xen_vcpu_nr(smp_processor_id()), NULL);
384 xen_cpu_bringup_again(stack: (unsigned long)task_pt_regs(current));
385 BUG();
386}
387
388#else /* !CONFIG_HOTPLUG_CPU */
389static int xen_pv_cpu_disable(void)
390{
391 return -ENOSYS;
392}
393
394static void xen_pv_cpu_die(unsigned int cpu)
395{
396 BUG();
397}
398
399static void xen_pv_cleanup_dead_cpu(unsigned int cpu)
400{
401 BUG();
402}
403
404static void __noreturn xen_pv_play_dead(void)
405{
406 BUG();
407}
408
409#endif
410static void stop_self(void *v)
411{
412 int cpu = smp_processor_id();
413
414 /* make sure we're not pinning something down */
415 load_cr3(swapper_pg_dir);
416 /* should set up a minimal gdt */
417
418 set_cpu_online(cpu, online: false);
419
420 HYPERVISOR_vcpu_op(VCPUOP_down, vcpuid: xen_vcpu_nr(cpu), NULL);
421 BUG();
422}
423
424static void xen_pv_stop_other_cpus(int wait)
425{
426 smp_call_function(func: stop_self, NULL, wait);
427}
428
429static irqreturn_t xen_irq_work_interrupt(int irq, void *dev_id)
430{
431 irq_work_run();
432 inc_irq_stat(apic_irq_work_irqs);
433
434 return IRQ_HANDLED;
435}
436
437static const struct smp_ops xen_smp_ops __initconst = {
438 .smp_prepare_boot_cpu = xen_pv_smp_prepare_boot_cpu,
439 .smp_prepare_cpus = xen_pv_smp_prepare_cpus,
440 .smp_cpus_done = xen_smp_cpus_done,
441
442 .kick_ap_alive = xen_pv_kick_ap,
443 .cpu_die = xen_pv_cpu_die,
444 .cleanup_dead_cpu = xen_pv_cleanup_dead_cpu,
445 .poll_sync_state = xen_pv_poll_sync_state,
446 .cpu_disable = xen_pv_cpu_disable,
447 .play_dead = xen_pv_play_dead,
448
449 .stop_other_cpus = xen_pv_stop_other_cpus,
450 .smp_send_reschedule = xen_smp_send_reschedule,
451
452 .send_call_func_ipi = xen_smp_send_call_function_ipi,
453 .send_call_func_single_ipi = xen_smp_send_call_function_single_ipi,
454};
455
456void __init xen_smp_init(void)
457{
458 smp_ops = xen_smp_ops;
459
460 /* Avoid searching for BIOS MP tables */
461 x86_init.mpparse.find_smp_config = x86_init_noop;
462 x86_init.mpparse.get_smp_config = _get_smp_config;
463}
464

source code of linux/arch/x86/xen/smp_pv.c