xref: /linux/arch/x86/kernel/kvmclock.c (revision 79790b6818e96c58fe2bffee1b418c16e64e7b80)
1 // SPDX-License-Identifier: GPL-2.0-or-later
2 /*  KVM paravirtual clock driver. A clocksource implementation
3     Copyright (C) 2008 Glauber de Oliveira Costa, Red Hat Inc.
4 */
5 
6 #include <linux/clocksource.h>
7 #include <linux/kvm_para.h>
8 #include <asm/pvclock.h>
9 #include <asm/msr.h>
10 #include <asm/apic.h>
11 #include <linux/percpu.h>
12 #include <linux/hardirq.h>
13 #include <linux/cpuhotplug.h>
14 #include <linux/sched.h>
15 #include <linux/sched/clock.h>
16 #include <linux/mm.h>
17 #include <linux/slab.h>
18 #include <linux/set_memory.h>
19 #include <linux/cc_platform.h>
20 
21 #include <asm/hypervisor.h>
22 #include <asm/x86_init.h>
23 #include <asm/kvmclock.h>
24 
25 static int kvmclock __initdata = 1;
26 static int kvmclock_vsyscall __initdata = 1;
27 static int msr_kvm_system_time __ro_after_init;
28 static int msr_kvm_wall_clock __ro_after_init;
29 static u64 kvm_sched_clock_offset __ro_after_init;
30 
parse_no_kvmclock(char * arg)31 static int __init parse_no_kvmclock(char *arg)
32 {
33 	kvmclock = 0;
34 	return 0;
35 }
36 early_param("no-kvmclock", parse_no_kvmclock);
37 
parse_no_kvmclock_vsyscall(char * arg)38 static int __init parse_no_kvmclock_vsyscall(char *arg)
39 {
40 	kvmclock_vsyscall = 0;
41 	return 0;
42 }
43 early_param("no-kvmclock-vsyscall", parse_no_kvmclock_vsyscall);
44 
45 /* Aligned to page sizes to match what's mapped via vsyscalls to userspace */
46 #define HVC_BOOT_ARRAY_SIZE \
47 	(PAGE_SIZE / sizeof(struct pvclock_vsyscall_time_info))
48 
49 static struct pvclock_vsyscall_time_info
50 			hv_clock_boot[HVC_BOOT_ARRAY_SIZE] __bss_decrypted __aligned(PAGE_SIZE);
51 static struct pvclock_wall_clock wall_clock __bss_decrypted;
52 static struct pvclock_vsyscall_time_info *hvclock_mem;
53 DEFINE_PER_CPU(struct pvclock_vsyscall_time_info *, hv_clock_per_cpu);
54 EXPORT_PER_CPU_SYMBOL_GPL(hv_clock_per_cpu);
55 
56 /*
57  * The wallclock is the time of day when we booted. Since then, some time may
58  * have elapsed since the hypervisor wrote the data. So we try to account for
59  * that with system time
60  */
kvm_get_wallclock(struct timespec64 * now)61 static void kvm_get_wallclock(struct timespec64 *now)
62 {
63 	wrmsrl(msr_kvm_wall_clock, slow_virt_to_phys(&wall_clock));
64 	preempt_disable();
65 	pvclock_read_wallclock(&wall_clock, this_cpu_pvti(), now);
66 	preempt_enable();
67 }
68 
kvm_set_wallclock(const struct timespec64 * now)69 static int kvm_set_wallclock(const struct timespec64 *now)
70 {
71 	return -ENODEV;
72 }
73 
kvm_clock_read(void)74 static u64 kvm_clock_read(void)
75 {
76 	u64 ret;
77 
78 	preempt_disable_notrace();
79 	ret = pvclock_clocksource_read_nowd(this_cpu_pvti());
80 	preempt_enable_notrace();
81 	return ret;
82 }
83 
kvm_clock_get_cycles(struct clocksource * cs)84 static u64 kvm_clock_get_cycles(struct clocksource *cs)
85 {
86 	return kvm_clock_read();
87 }
88 
kvm_sched_clock_read(void)89 static noinstr u64 kvm_sched_clock_read(void)
90 {
91 	return pvclock_clocksource_read_nowd(this_cpu_pvti()) - kvm_sched_clock_offset;
92 }
93 
kvm_sched_clock_init(bool stable)94 static inline void kvm_sched_clock_init(bool stable)
95 {
96 	if (!stable)
97 		clear_sched_clock_stable();
98 	kvm_sched_clock_offset = kvm_clock_read();
99 	paravirt_set_sched_clock(kvm_sched_clock_read);
100 
101 	pr_info("kvm-clock: using sched offset of %llu cycles",
102 		kvm_sched_clock_offset);
103 
104 	BUILD_BUG_ON(sizeof(kvm_sched_clock_offset) >
105 		sizeof(((struct pvclock_vcpu_time_info *)NULL)->system_time));
106 }
107 
108 /*
109  * If we don't do that, there is the possibility that the guest
110  * will calibrate under heavy load - thus, getting a lower lpj -
111  * and execute the delays themselves without load. This is wrong,
112  * because no delay loop can finish beforehand.
113  * Any heuristics is subject to fail, because ultimately, a large
114  * poll of guests can be running and trouble each other. So we preset
115  * lpj here
116  */
kvm_get_tsc_khz(void)117 static unsigned long kvm_get_tsc_khz(void)
118 {
119 	setup_force_cpu_cap(X86_FEATURE_TSC_KNOWN_FREQ);
120 	return pvclock_tsc_khz(this_cpu_pvti());
121 }
122 
kvm_get_preset_lpj(void)123 static void __init kvm_get_preset_lpj(void)
124 {
125 	unsigned long khz;
126 	u64 lpj;
127 
128 	khz = kvm_get_tsc_khz();
129 
130 	lpj = ((u64)khz * 1000);
131 	do_div(lpj, HZ);
132 	preset_lpj = lpj;
133 }
134 
kvm_check_and_clear_guest_paused(void)135 bool kvm_check_and_clear_guest_paused(void)
136 {
137 	struct pvclock_vsyscall_time_info *src = this_cpu_hvclock();
138 	bool ret = false;
139 
140 	if (!src)
141 		return ret;
142 
143 	if ((src->pvti.flags & PVCLOCK_GUEST_STOPPED) != 0) {
144 		src->pvti.flags &= ~PVCLOCK_GUEST_STOPPED;
145 		pvclock_touch_watchdogs();
146 		ret = true;
147 	}
148 	return ret;
149 }
150 
kvm_cs_enable(struct clocksource * cs)151 static int kvm_cs_enable(struct clocksource *cs)
152 {
153 	vclocks_set_used(VDSO_CLOCKMODE_PVCLOCK);
154 	return 0;
155 }
156 
157 static struct clocksource kvm_clock = {
158 	.name	= "kvm-clock",
159 	.read	= kvm_clock_get_cycles,
160 	.rating	= 400,
161 	.mask	= CLOCKSOURCE_MASK(64),
162 	.flags	= CLOCK_SOURCE_IS_CONTINUOUS,
163 	.id     = CSID_X86_KVM_CLK,
164 	.enable	= kvm_cs_enable,
165 };
166 
kvm_register_clock(char * txt)167 static void kvm_register_clock(char *txt)
168 {
169 	struct pvclock_vsyscall_time_info *src = this_cpu_hvclock();
170 	u64 pa;
171 
172 	if (!src)
173 		return;
174 
175 	pa = slow_virt_to_phys(&src->pvti) | 0x01ULL;
176 	wrmsrl(msr_kvm_system_time, pa);
177 	pr_debug("kvm-clock: cpu %d, msr %llx, %s", smp_processor_id(), pa, txt);
178 }
179 
kvm_save_sched_clock_state(void)180 static void kvm_save_sched_clock_state(void)
181 {
182 }
183 
kvm_restore_sched_clock_state(void)184 static void kvm_restore_sched_clock_state(void)
185 {
186 	kvm_register_clock("primary cpu clock, resume");
187 }
188 
189 #ifdef CONFIG_X86_LOCAL_APIC
kvm_setup_secondary_clock(void)190 static void kvm_setup_secondary_clock(void)
191 {
192 	kvm_register_clock("secondary cpu clock");
193 }
194 #endif
195 
kvmclock_disable(void)196 void kvmclock_disable(void)
197 {
198 	if (msr_kvm_system_time)
199 		native_write_msr(msr_kvm_system_time, 0, 0);
200 }
201 
kvmclock_init_mem(void)202 static void __init kvmclock_init_mem(void)
203 {
204 	unsigned long ncpus;
205 	unsigned int order;
206 	struct page *p;
207 	int r;
208 
209 	if (HVC_BOOT_ARRAY_SIZE >= num_possible_cpus())
210 		return;
211 
212 	ncpus = num_possible_cpus() - HVC_BOOT_ARRAY_SIZE;
213 	order = get_order(ncpus * sizeof(*hvclock_mem));
214 
215 	p = alloc_pages(GFP_KERNEL, order);
216 	if (!p) {
217 		pr_warn("%s: failed to alloc %d pages", __func__, (1U << order));
218 		return;
219 	}
220 
221 	hvclock_mem = page_address(p);
222 
223 	/*
224 	 * hvclock is shared between the guest and the hypervisor, must
225 	 * be mapped decrypted.
226 	 */
227 	if (cc_platform_has(CC_ATTR_GUEST_MEM_ENCRYPT)) {
228 		r = set_memory_decrypted((unsigned long) hvclock_mem,
229 					 1UL << order);
230 		if (r) {
231 			__free_pages(p, order);
232 			hvclock_mem = NULL;
233 			pr_warn("kvmclock: set_memory_decrypted() failed. Disabling\n");
234 			return;
235 		}
236 	}
237 
238 	memset(hvclock_mem, 0, PAGE_SIZE << order);
239 }
240 
kvm_setup_vsyscall_timeinfo(void)241 static int __init kvm_setup_vsyscall_timeinfo(void)
242 {
243 	if (!kvm_para_available() || !kvmclock || nopv)
244 		return 0;
245 
246 	kvmclock_init_mem();
247 
248 #ifdef CONFIG_X86_64
249 	if (per_cpu(hv_clock_per_cpu, 0) && kvmclock_vsyscall) {
250 		u8 flags;
251 
252 		flags = pvclock_read_flags(&hv_clock_boot[0].pvti);
253 		if (!(flags & PVCLOCK_TSC_STABLE_BIT))
254 			return 0;
255 
256 		kvm_clock.vdso_clock_mode = VDSO_CLOCKMODE_PVCLOCK;
257 	}
258 #endif
259 
260 	return 0;
261 }
262 early_initcall(kvm_setup_vsyscall_timeinfo);
263 
kvmclock_setup_percpu(unsigned int cpu)264 static int kvmclock_setup_percpu(unsigned int cpu)
265 {
266 	struct pvclock_vsyscall_time_info *p = per_cpu(hv_clock_per_cpu, cpu);
267 
268 	/*
269 	 * The per cpu area setup replicates CPU0 data to all cpu
270 	 * pointers. So carefully check. CPU0 has been set up in init
271 	 * already.
272 	 */
273 	if (!cpu || (p && p != per_cpu(hv_clock_per_cpu, 0)))
274 		return 0;
275 
276 	/* Use the static page for the first CPUs, allocate otherwise */
277 	if (cpu < HVC_BOOT_ARRAY_SIZE)
278 		p = &hv_clock_boot[cpu];
279 	else if (hvclock_mem)
280 		p = hvclock_mem + cpu - HVC_BOOT_ARRAY_SIZE;
281 	else
282 		return -ENOMEM;
283 
284 	per_cpu(hv_clock_per_cpu, cpu) = p;
285 	return p ? 0 : -ENOMEM;
286 }
287 
kvmclock_init(void)288 void __init kvmclock_init(void)
289 {
290 	u8 flags;
291 
292 	if (!kvm_para_available() || !kvmclock)
293 		return;
294 
295 	if (kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE2)) {
296 		msr_kvm_system_time = MSR_KVM_SYSTEM_TIME_NEW;
297 		msr_kvm_wall_clock = MSR_KVM_WALL_CLOCK_NEW;
298 	} else if (kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE)) {
299 		msr_kvm_system_time = MSR_KVM_SYSTEM_TIME;
300 		msr_kvm_wall_clock = MSR_KVM_WALL_CLOCK;
301 	} else {
302 		return;
303 	}
304 
305 	if (cpuhp_setup_state(CPUHP_BP_PREPARE_DYN, "kvmclock:setup_percpu",
306 			      kvmclock_setup_percpu, NULL) < 0) {
307 		return;
308 	}
309 
310 	pr_info("kvm-clock: Using msrs %x and %x",
311 		msr_kvm_system_time, msr_kvm_wall_clock);
312 
313 	this_cpu_write(hv_clock_per_cpu, &hv_clock_boot[0]);
314 	kvm_register_clock("primary cpu clock");
315 	pvclock_set_pvti_cpu0_va(hv_clock_boot);
316 
317 	if (kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE_STABLE_BIT))
318 		pvclock_set_flags(PVCLOCK_TSC_STABLE_BIT);
319 
320 	flags = pvclock_read_flags(&hv_clock_boot[0].pvti);
321 	kvm_sched_clock_init(flags & PVCLOCK_TSC_STABLE_BIT);
322 
323 	x86_platform.calibrate_tsc = kvm_get_tsc_khz;
324 	x86_platform.calibrate_cpu = kvm_get_tsc_khz;
325 	x86_platform.get_wallclock = kvm_get_wallclock;
326 	x86_platform.set_wallclock = kvm_set_wallclock;
327 #ifdef CONFIG_X86_LOCAL_APIC
328 	x86_cpuinit.early_percpu_clock_init = kvm_setup_secondary_clock;
329 #endif
330 	x86_platform.save_sched_clock_state = kvm_save_sched_clock_state;
331 	x86_platform.restore_sched_clock_state = kvm_restore_sched_clock_state;
332 	kvm_get_preset_lpj();
333 
334 	/*
335 	 * X86_FEATURE_NONSTOP_TSC is TSC runs at constant rate
336 	 * with P/T states and does not stop in deep C-states.
337 	 *
338 	 * Invariant TSC exposed by host means kvmclock is not necessary:
339 	 * can use TSC as clocksource.
340 	 *
341 	 */
342 	if (boot_cpu_has(X86_FEATURE_CONSTANT_TSC) &&
343 	    boot_cpu_has(X86_FEATURE_NONSTOP_TSC) &&
344 	    !check_tsc_unstable())
345 		kvm_clock.rating = 299;
346 
347 	clocksource_register_hz(&kvm_clock, NSEC_PER_SEC);
348 	pv_info.name = "KVM";
349 }
350