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Re: [PATCH v2 1/2] arm/hvf: Optimize and simplify WFI handling
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From: |
Peter Collingbourne |
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Subject: |
Re: [PATCH v2 1/2] arm/hvf: Optimize and simplify WFI handling |
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Date: |
Tue, 1 Dec 2020 17:52:52 -0800 |
On Tue, Dec 1, 2020 at 5:39 PM Alexander Graf <agraf@csgraf.de> wrote:
>
>
> On 02.12.20 02:32, Peter Collingbourne wrote:
> > On Tue, Dec 1, 2020 at 3:24 PM Alexander Graf <agraf@csgraf.de> wrote:
> >>
> >> On 01.12.20 22:00, Peter Collingbourne wrote:
> >>> 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();
> >>
> >> I think you touched based on it in a previous thread, but would you mind
> >> to explain again why mach_absolute_time() is the right thing to check
> >> cval against? If I read the headers correctly, the cnvt_off register
> >> should be 0, so cntvct should be the reference time, no?
> > In my experiments I've found that CNTPCT_EL0 and CNTVCT_EL0 are the
> > same when read on the host (i.e. host CNTVOFF_EL2 = 0). When we look
> > at the guest we see that CNTPCT_EL0 corresponds to
> > mach_absolute_time() on the host and not host CNTPCT_EL0 (if you look
> > at XNU kernel sources you will see that mach_absolute_time() reads
> > CNTPCT_EL0 and adds a constant corresponding to the amount of time
> > that the machine spends asleep) so I think that what's going on at the
> > hypervisor level is that guest CNTPOFF_EL2 is being set to the same
> > constant to make it correspond to mach_absolute_time().
>
>
> Yes, I can absolutely see how it's different from CNTPCT, but it should
> be identical to CNTVCT_EL0 inside QEMU, no?
Not necessarily. It's possible for the guest to observe a different
CNTVCT_EL0 either because CNTPOFF_EL2 is set to a non-zero value or
because the hypervisor is secretly adding the "time spent asleep"
constant to CNTVOFF_EL2 on top of the value that we set it to via the
API.
Peter