Configure the pKVM hypervisor tracing clock with the kernel boot clock.
For tracing purpose, the boot clock is interesting as it doesn't stop on
suspend. However, it is corrected on a regular basis, which implies we
need to re-evaluate it every once in a while.
Cc: John Stultz <jstu...@google.com>
Cc: Thomas Gleixner <t...@linutronix.de>
Cc: Stephen Boyd <sb...@kernel.org>
Cc: Christopher S. Hall <christopher.s.h...@intel.com>
Cc: Richard Cochran <richardcoch...@gmail.com>
Signed-off-by: Vincent Donnefort <vdonnef...@google.com>
diff --git a/arch/arm64/include/asm/kvm_asm.h b/arch/arm64/include/asm/kvm_asm.h
index 437ac948d136..d122d79718a0 100644
--- a/arch/arm64/include/asm/kvm_asm.h
+++ b/arch/arm64/include/asm/kvm_asm.h
@@ -87,6 +87,7 @@ enum __kvm_host_smccc_func {
__KVM_HOST_SMCCC_FUNC___pkvm_vcpu_load,
__KVM_HOST_SMCCC_FUNC___pkvm_vcpu_put,
__KVM_HOST_SMCCC_FUNC___pkvm_tlb_flush_vmid,
+ __KVM_HOST_SMCCC_FUNC___pkvm_update_clock_tracing,
__KVM_HOST_SMCCC_FUNC___pkvm_load_tracing,
__KVM_HOST_SMCCC_FUNC___pkvm_unload_tracing,
__KVM_HOST_SMCCC_FUNC___pkvm_enable_tracing,
diff --git a/arch/arm64/kvm/hyp/include/nvhe/trace.h
b/arch/arm64/kvm/hyp/include/nvhe/trace.h
index 996e90c0974f..4e11dcdf049b 100644
--- a/arch/arm64/kvm/hyp/include/nvhe/trace.h
+++ b/arch/arm64/kvm/hyp/include/nvhe/trace.h
@@ -7,6 +7,7 @@
void *tracing_reserve_entry(unsigned long length);
void tracing_commit_entry(void);
+void __pkvm_update_clock_tracing(u32 mult, u32 shift, u64 epoch_ns, u64
epoch_cyc);
int __pkvm_load_tracing(unsigned long desc_va, size_t desc_size);
void __pkvm_unload_tracing(void);
int __pkvm_enable_tracing(bool enable);
@@ -15,6 +16,8 @@ int __pkvm_swap_reader_tracing(unsigned int cpu);
static inline void *tracing_reserve_entry(unsigned long length) { return NULL;
}
static inline void tracing_commit_entry(void) { }
+static inline
+void __pkvm_update_clock_tracing(u32 mult, u32 shift, u64 epoch_ns, u64
epoch_cyc) { }
static inline int __pkvm_load_tracing(unsigned long desc_va, size_t desc_size)
{ return -ENODEV; }
static inline void __pkvm_unload_tracing(void) { }
static inline int __pkvm_enable_tracing(bool enable) { return -ENODEV; }
diff --git a/arch/arm64/kvm/hyp/nvhe/hyp-main.c
b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
index 68b98547666b..c73229fb5e1b 100644
--- a/arch/arm64/kvm/hyp/nvhe/hyp-main.c
+++ b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
@@ -571,6 +571,18 @@ static void handle___pkvm_teardown_vm(struct
kvm_cpu_context *host_ctxt)
cpu_reg(host_ctxt, 1) = __pkvm_teardown_vm(handle);
}
+static void handle___pkvm_update_clock_tracing(struct kvm_cpu_context
*host_ctxt)
+{
+ DECLARE_REG(u32, mult, host_ctxt, 1);
+ DECLARE_REG(u32, shift, host_ctxt, 2);
+ DECLARE_REG(u64, epoch_ns, host_ctxt, 3);
+ DECLARE_REG(u64, epoch_cyc, host_ctxt, 4);
+
+ __pkvm_update_clock_tracing(mult, shift, epoch_ns, epoch_cyc);
+
+ cpu_reg(host_ctxt, 1) = 0;
+}
+
static void handle___pkvm_load_tracing(struct kvm_cpu_context *host_ctxt)
{
DECLARE_REG(unsigned long, desc_hva, host_ctxt, 1);
@@ -639,6 +651,7 @@ static const hcall_t host_hcall[] = {
HANDLE_FUNC(__pkvm_vcpu_load),
HANDLE_FUNC(__pkvm_vcpu_put),
HANDLE_FUNC(__pkvm_tlb_flush_vmid),
+ HANDLE_FUNC(__pkvm_update_clock_tracing),
HANDLE_FUNC(__pkvm_load_tracing),
HANDLE_FUNC(__pkvm_unload_tracing),
HANDLE_FUNC(__pkvm_enable_tracing),
diff --git a/arch/arm64/kvm/hyp/nvhe/trace.c b/arch/arm64/kvm/hyp/nvhe/trace.c
index f9949b243844..32fd889315f0 100644
--- a/arch/arm64/kvm/hyp/nvhe/trace.c
+++ b/arch/arm64/kvm/hyp/nvhe/trace.c
@@ -249,3 +249,19 @@ int __pkvm_swap_reader_tracing(unsigned int cpu)
return ret;
}
+
+void __pkvm_update_clock_tracing(u32 mult, u32 shift, u64 epoch_ns, u64
epoch_cyc)
+{
+ int cpu;
+
+ /* After this loop, all CPUs are observing the new bank... */
+ for (cpu = 0; cpu < hyp_nr_cpus; cpu++) {
+ struct simple_rb_per_cpu *simple_rb =
per_cpu_ptr(trace_buffer.simple_rbs, cpu);
+
+ while (READ_ONCE(simple_rb->status) == SIMPLE_RB_WRITING)
+ ;
+ }
+
+ /* ...we can now override the old one and swap. */
+ trace_clock_update(mult, shift, epoch_ns, epoch_cyc);
+}
diff --git a/arch/arm64/kvm/hyp_trace.c b/arch/arm64/kvm/hyp_trace.c
index ccac2ecaf96f..a6664a03f8a9 100644
--- a/arch/arm64/kvm/hyp_trace.c
+++ b/arch/arm64/kvm/hyp_trace.c
@@ -5,6 +5,7 @@
*/
#include <linux/trace_remote.h>
+#include <linux/tracefs.h>
#include <linux/simple_ring_buffer.h>
#include <asm/kvm_host.h>
@@ -12,6 +13,121 @@
#include "hyp_trace.h"
+/* Same 10min used by clocksource when width is more than 32-bits */
+#define CLOCK_MAX_CONVERSION_S 600
+/*
+ * Time to give for the clock init. Long enough to get a good mult/shift
+ * estimation. Short enough to not delay the tracing start too much.
+ */
+#define CLOCK_INIT_MS 100
+/*
+ * Time between clock checks. Must be small enough to catch clock deviation
when
+ * it is still tiny.
+ */
+#define CLOCK_UPDATE_MS 500
+
+static struct hyp_trace_clock {
+ u64 cycles;
+ u64 cyc_overflow64;
+ u64 boot;
+ u32 mult;
+ u32 shift;
+ struct delayed_work work;
+ struct completion ready;
+ struct mutex lock;
+ bool running;
+} hyp_clock;
+
+static void __hyp_clock_work(struct work_struct *work)
+{
+ struct delayed_work *dwork = to_delayed_work(work);
+ struct hyp_trace_clock *hyp_clock;
+ struct system_time_snapshot snap;
+ u64 rate, delta_cycles;
+ u64 boot, delta_boot;
+
+ hyp_clock = container_of(dwork, struct hyp_trace_clock, work);
+
+ ktime_get_snapshot(&snap);
+ boot = ktime_to_ns(snap.boot);
+
+ delta_boot = boot - hyp_clock->boot;
+ delta_cycles = snap.cycles - hyp_clock->cycles;
+
+ /* Compare hyp clock with the kernel boot clock */
+ if (hyp_clock->mult) {
+ u64 err, cur = delta_cycles;
+
+ if (WARN_ON_ONCE(cur >= hyp_clock->cyc_overflow64)) {
+ __uint128_t tmp = (__uint128_t)cur * hyp_clock->mult;
+
+ cur = tmp >> hyp_clock->shift;
+ } else {
+ cur *= hyp_clock->mult;
+ cur >>= hyp_clock->shift;
+ }
+ cur += hyp_clock->boot;
+
+ err = abs_diff(cur, boot);
+ /* No deviation, only update epoch if necessary */
+ if (!err) {
+ if (delta_cycles >= (hyp_clock->cyc_overflow64 >> 1))
+ goto fast_forward;
+
+ goto resched;
+ }
+
+ /* Warn if the error is above tracing precision (1us) */
+ if (err > NSEC_PER_USEC)
+ pr_warn_ratelimited("hyp trace clock off by %lluus\n",
+ err / NSEC_PER_USEC);
+ }
+
+ rate = div64_u64(delta_cycles * NSEC_PER_SEC, delta_boot);
+
+ clocks_calc_mult_shift(&hyp_clock->mult, &hyp_clock->shift,
+ rate, NSEC_PER_SEC, CLOCK_MAX_CONVERSION_S);
+
+ /* Add a comfortable 50% margin */
+ hyp_clock->cyc_overflow64 = (U64_MAX / hyp_clock->mult) >> 1;
+
+fast_forward:
+ hyp_clock->cycles = snap.cycles;
+ hyp_clock->boot = boot;
+ kvm_call_hyp_nvhe(__pkvm_update_clock_tracing, hyp_clock->mult,
+ hyp_clock->shift, hyp_clock->boot, hyp_clock->cycles);
+ complete(&hyp_clock->ready);
+
+resched:
+ schedule_delayed_work(&hyp_clock->work,
+ msecs_to_jiffies(CLOCK_UPDATE_MS));
+}
+
+static void hyp_trace_clock_enable(struct hyp_trace_clock *hyp_clock, bool
enable)
+{
+ struct system_time_snapshot snap;
+
+ if (hyp_clock->running == enable)
+ return;
+
+ if (!enable) {
+ cancel_delayed_work_sync(&hyp_clock->work);
+ hyp_clock->running = false;
+ }
+
+ ktime_get_snapshot(&snap);
+
+ hyp_clock->boot = ktime_to_ns(snap.boot);
+ hyp_clock->cycles = snap.cycles;
+ hyp_clock->mult = 0;
+
+ init_completion(&hyp_clock->ready);
+ INIT_DELAYED_WORK(&hyp_clock->work, __hyp_clock_work);
+ schedule_delayed_work(&hyp_clock->work,
msecs_to_jiffies(CLOCK_INIT_MS));
+ wait_for_completion(&hyp_clock->ready);
+ hyp_clock->running = true;
+}
+
/* Access to this struct within the trace_remote_callbacks are protected by
the trace_remote lock */
struct hyp_trace_buffer {
struct hyp_trace_desc *desc;
@@ -173,6 +289,8 @@ static void hyp_trace_unload(struct trace_buffer_desc
*desc, void *priv)
static int hyp_trace_enable_tracing(bool enable, void *priv)
{
+ hyp_trace_clock_enable(&hyp_clock, enable);
+
return kvm_call_hyp_nvhe(__pkvm_enable_tracing, enable);
}
@@ -191,7 +309,22 @@ static int hyp_trace_enable_event(unsigned short id, bool
enable, void *priv)
return 0;
}
+static int hyp_trace_clock_show(struct seq_file *m, void *v)
+{
+ seq_puts(m, "[boot]\n");
+
+ return 0;
+}
+DEFINE_SHOW_ATTRIBUTE(hyp_trace_clock);
+
+static int hyp_trace_init_tracefs(struct dentry *d, void *priv)
+{
+ return tracefs_create_file("trace_clock", 0440, d, NULL,
&hyp_trace_clock_fops) ?
+ 0 : -ENOMEM;
+}
+
static struct trace_remote_callbacks trace_remote_callbacks = {
+ .init = hyp_trace_init_tracefs,
.load_trace_buffer = hyp_trace_load,
.unload_trace_buffer = hyp_trace_unload,
.enable_tracing = hyp_trace_enable_tracing,
--
2.49.0.1101.gccaa498523-goog
