[PATCH v2 1/2] arm/hvf: Optimize and simplify WFI handling

[Peter Collingbourne]

Sleep on WFx until the VTIMER is due but allow ourselves to be woken
up on IPI.

Signed-off-by: Peter Collingbourne <pcc@google.com>
---
v2:
- simplify locking further
- wait indefinitely on disabled or masked timers

 accel/hvf/hvf-cpus.c     |   5 +-
 include/sysemu/hvf_int.h |   3 +-
 target/arm/hvf/hvf.c     | 116 ++++++++++++++-------------------------
 3 files changed, 43 insertions(+), 81 deletions(-)

diff --git a/accel/hvf/hvf-cpus.c b/accel/hvf/hvf-cpus.c
index 4360f64671..b2c8fb57f6 100644
--- a/accel/hvf/hvf-cpus.c
+++ b/accel/hvf/hvf-cpus.c
@@ -344,9 +344,8 @@ static int hvf_init_vcpu(CPUState *cpu)
     sigact.sa_handler = dummy_signal;
     sigaction(SIG_IPI, &sigact, NULL);
 
-    pthread_sigmask(SIG_BLOCK, NULL, &set);
-    sigdelset(&set, SIG_IPI);
-    pthread_sigmask(SIG_SETMASK, &set, NULL);
+    pthread_sigmask(SIG_BLOCK, NULL, &cpu->hvf->unblock_ipi_mask);
+    sigdelset(&cpu->hvf->unblock_ipi_mask, SIG_IPI);
 
 #ifdef __aarch64__
     r = hv_vcpu_create(&cpu->hvf->fd, (hv_vcpu_exit_t **)&cpu->hvf->exit, 
NULL);
diff --git a/include/sysemu/hvf_int.h b/include/sysemu/hvf_int.h
index c56baa3ae8..13adf6ea77 100644
--- a/include/sysemu/hvf_int.h
+++ b/include/sysemu/hvf_int.h
@@ -62,8 +62,7 @@ extern HVFState *hvf_state;
 struct hvf_vcpu_state {
     uint64_t fd;
     void *exit;
-    struct timespec ts;
-    bool sleeping;
+    sigset_t unblock_ipi_mask;
 };
 
 void assert_hvf_ok(hv_return_t ret);
diff --git a/target/arm/hvf/hvf.c b/target/arm/hvf/hvf.c
index 8fe10966d2..3321d48aa2 100644
--- a/target/arm/hvf/hvf.c
+++ b/target/arm/hvf/hvf.c
@@ -2,6 +2,7 @@
  * QEMU Hypervisor.framework support for Apple Silicon
 
  * Copyright 2020 Alexander Graf <agraf@csgraf.de>
+ * Copyright 2020 Google LLC
  *
  * This work is licensed under the terms of the GNU GPL, version 2 or later.
  * See the COPYING file in the top-level directory.
@@ -18,6 +19,7 @@
 #include "sysemu/hw_accel.h"
 
 #include <Hypervisor/Hypervisor.h>
+#include <mach/mach_time.h>
 
 #include "exec/address-spaces.h"
 #include "hw/irq.h"
@@ -320,18 +322,8 @@ int hvf_arch_init_vcpu(CPUState *cpu)
 
 void hvf_kick_vcpu_thread(CPUState *cpu)
 {
-    if (cpu->hvf->sleeping) {
-        /*
-         * When sleeping, make sure we always send signals. Also, clear the
-         * timespec, so that an IPI that arrives between setting hvf->sleeping
-         * and the nanosleep syscall still aborts the sleep.
-         */
-        cpu->thread_kicked = false;
-        cpu->hvf->ts = (struct timespec){ };
-        cpus_kick_thread(cpu);
-    } else {
-        hv_vcpus_exit(&cpu->hvf->fd, 1);
-    }
+    cpus_kick_thread(cpu);
+    hv_vcpus_exit(&cpu->hvf->fd, 1);
 }
 
 static int hvf_inject_interrupts(CPUState *cpu)
@@ -349,6 +341,18 @@ static int hvf_inject_interrupts(CPUState *cpu)
     return 0;
 }
 
+static void hvf_wait_for_ipi(CPUState *cpu, struct timespec *ts)
+{
+    /*
+     * Use pselect to sleep so that other threads can IPI us while we're
+     * sleeping.
+     */
+    qatomic_mb_set(&cpu->thread_kicked, false);
+    qemu_mutex_unlock_iothread();
+    pselect(0, 0, 0, 0, ts, &cpu->hvf->unblock_ipi_mask);
+    qemu_mutex_lock_iothread();
+}
+
 int hvf_vcpu_exec(CPUState *cpu)
 {
     ARMCPU *arm_cpu = ARM_CPU(cpu);
@@ -357,15 +361,11 @@ int hvf_vcpu_exec(CPUState *cpu)
     hv_return_t r;
     int ret = 0;
 
-    qemu_mutex_unlock_iothread();
-
     do {
         bool advance_pc = false;
 
-        qemu_mutex_lock_iothread();
         current_cpu = cpu;
         qemu_wait_io_event_common(cpu);
-        qemu_mutex_unlock_iothread();
 
         flush_cpu_state(cpu);
 
@@ -374,10 +374,10 @@ int hvf_vcpu_exec(CPUState *cpu)
         }
 
         if (cpu->halted) {
-            qemu_mutex_lock_iothread();
             return EXCP_HLT;
         }
 
+        qemu_mutex_unlock_iothread();
         assert_hvf_ok(hv_vcpu_run(cpu->hvf->fd));
 
         /* handle VMEXIT */
@@ -385,15 +385,14 @@ int hvf_vcpu_exec(CPUState *cpu)
         uint64_t syndrome = hvf_exit->exception.syndrome;
         uint32_t ec = syn_get_ec(syndrome);
 
+        qemu_mutex_lock_iothread();
         switch (exit_reason) {
         case HV_EXIT_REASON_EXCEPTION:
             /* This is the main one, handle below. */
             break;
         case HV_EXIT_REASON_VTIMER_ACTIVATED:
-            qemu_mutex_lock_iothread();
             current_cpu = cpu;
             qemu_set_irq(arm_cpu->gt_timer_outputs[GTIMER_VIRT], 1);
-            qemu_mutex_unlock_iothread();
             continue;
         case HV_EXIT_REASON_CANCELED:
             /* we got kicked, no exit to process */
@@ -413,7 +412,6 @@ int hvf_vcpu_exec(CPUState *cpu)
             uint32_t srt = (syndrome >> 16) & 0x1f;
             uint64_t val = 0;
 
-            qemu_mutex_lock_iothread();
             current_cpu = cpu;
 
             DPRINTF("data abort: [pc=0x%llx va=0x%016llx pa=0x%016llx isv=%x "
@@ -446,8 +444,6 @@ int hvf_vcpu_exec(CPUState *cpu)
                 hvf_set_reg(cpu, srt, val);
             }
 
-            qemu_mutex_unlock_iothread();
-
             advance_pc = true;
             break;
         }
@@ -493,68 +489,40 @@ int hvf_vcpu_exec(CPUState *cpu)
         case EC_WFX_TRAP:
             if (!(syndrome & WFX_IS_WFE) && !(cpu->interrupt_request &
                 (CPU_INTERRUPT_HARD | CPU_INTERRUPT_FIQ))) {
-                uint64_t cval, ctl, val, diff, now;
+                advance_pc = true;
 
-                /* Set up a local timer for vtimer if necessary ... */
-                r = hv_vcpu_get_sys_reg(cpu->hvf->fd, HV_SYS_REG_CNTV_CTL_EL0, 
&ctl);
-                assert_hvf_ok(r);
-                r = hv_vcpu_get_sys_reg(cpu->hvf->fd, 
HV_SYS_REG_CNTV_CVAL_EL0, &cval);
+                uint64_t ctl;
+                r = hv_vcpu_get_sys_reg(cpu->hvf->fd, HV_SYS_REG_CNTV_CTL_EL0,
+                                        &ctl);
                 assert_hvf_ok(r);
 
-                asm volatile("mrs %0, cntvct_el0" : "=r"(val));
-                diff = cval - val;
-
-                now = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) /
-                      gt_cntfrq_period_ns(arm_cpu);
-
-                /* Timer disabled or masked, just wait for long */
                 if (!(ctl & 1) || (ctl & 2)) {
-                    diff = (120 * NANOSECONDS_PER_SECOND) /
-                           gt_cntfrq_period_ns(arm_cpu);
+                    /* Timer disabled or masked, just wait for an IPI. */
+                    hvf_wait_for_ipi(cpu, NULL);
+                    break;
                 }
 
-                if (diff < INT64_MAX) {
-                    uint64_t ns = diff * gt_cntfrq_period_ns(arm_cpu);
-                    struct timespec *ts = &cpu->hvf->ts;
-
-                    *ts = (struct timespec){
-                        .tv_sec = ns / NANOSECONDS_PER_SECOND,
-                        .tv_nsec = ns % NANOSECONDS_PER_SECOND,
-                    };
-
-                    /*
-                     * Waking up easily takes 1ms, don't go to sleep for 
smaller
-                     * time periods than 2ms.
-                     */
-                    if (!ts->tv_sec && (ts->tv_nsec < (SCALE_MS * 2))) {
-                        advance_pc = true;
-                        break;
-                    }
-
-                    /* Set cpu->hvf->sleeping so that we get a SIG_IPI signal. 
*/
-                    cpu->hvf->sleeping = true;
-                    smp_mb();
-
-                    /* Bail out if we received an IRQ meanwhile */
-                    if (cpu->thread_kicked || (cpu->interrupt_request &
-                        (CPU_INTERRUPT_HARD | CPU_INTERRUPT_FIQ))) {
-                        cpu->hvf->sleeping = false;
-                        break;
-                    }
-
-                    /* nanosleep returns on signal, so we wake up on kick. */
-                    nanosleep(ts, NULL);
-
-                    /* Out of sleep - either naturally or because of a kick */
-                    cpu->hvf->sleeping = false;
+                uint64_t cval;
+                r = hv_vcpu_get_sys_reg(cpu->hvf->fd, HV_SYS_REG_CNTV_CVAL_EL0,
+                                        &cval);
+                assert_hvf_ok(r);
+
+                int64_t ticks_to_sleep = cval - mach_absolute_time();
+                if (ticks_to_sleep < 0) {
+                    break;
                 }
 
-                advance_pc = true;
+                uint64_t seconds = ticks_to_sleep / arm_cpu->gt_cntfrq_hz;
+                uint64_t nanos =
+                    (ticks_to_sleep - arm_cpu->gt_cntfrq_hz * seconds) *
+                    1000000000 / arm_cpu->gt_cntfrq_hz;
+                struct timespec ts = { seconds, nanos };
+
+                hvf_wait_for_ipi(cpu, &ts);
             }
             break;
         case EC_AA64_HVC:
             cpu_synchronize_state(cpu);
-            qemu_mutex_lock_iothread();
             current_cpu = cpu;
             if (arm_is_psci_call(arm_cpu, EXCP_HVC)) {
                 arm_handle_psci_call(arm_cpu);
@@ -562,11 +530,9 @@ int hvf_vcpu_exec(CPUState *cpu)
                 DPRINTF("unknown HVC! %016llx", env->xregs[0]);
                 env->xregs[0] = -1;
             }
-            qemu_mutex_unlock_iothread();
             break;
         case EC_AA64_SMC:
             cpu_synchronize_state(cpu);
-            qemu_mutex_lock_iothread();
             current_cpu = cpu;
             if (arm_is_psci_call(arm_cpu, EXCP_SMC)) {
                 arm_handle_psci_call(arm_cpu);
@@ -575,7 +541,6 @@ int hvf_vcpu_exec(CPUState *cpu)
                 env->xregs[0] = -1;
                 env->pc += 4;
             }
-            qemu_mutex_unlock_iothread();
             break;
         default:
             cpu_synchronize_state(cpu);
@@ -596,7 +561,6 @@ int hvf_vcpu_exec(CPUState *cpu)
         }
     } while (ret == 0);
 
-    qemu_mutex_lock_iothread();
     current_cpu = cpu;
 
     return ret;
-- 
2.29.2.454.gaff20da3a2-goog