FreeBSD/Linux Kernel Cross Reference
sys/dev/kvm_clock/kvm_clock.c

     /*-
      * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
      *
      * Copyright (c) 2014 Bryan Venteicher <bryanv@FreeBSD.org>
      * Copyright (c) 2021 Mathieu Chouquet-Stringer
      * Copyright (c) 2021 Juniper Networks, Inc.
      * Copyright (c) 2021 Klara, Inc.
      *
      * Redistribution and use in source and binary forms, with or without
     * modification, are permitted provided that the following conditions
     * are met:
     * 1. Redistributions of source code must retain the above copyright
     *    notice, this list of conditions and the following disclaimer.
     * 2. Redistributions in binary form must reproduce the above copyright
     *    notice, this list of conditions and the following disclaimer in the
     *    documentation and/or other materials provided with the distribution.
     *
     * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
     * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
     * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     * SUCH DAMAGE.
     */
    
    /*
     * Linux KVM paravirtual clock support
     *
     * References:
     *     - [1] https://www.kernel.org/doc/html/latest/virt/kvm/cpuid.html
     *     - [2] https://www.kernel.org/doc/html/latest/virt/kvm/msr.html
     */
    
    #include <sys/cdefs.h>
    __FBSDID("$FreeBSD$");
    
    #include <sys/param.h>
    #include <sys/bus.h>
    #include <sys/domainset.h>
    #include <sys/kernel.h>
    #include <sys/malloc.h>
    #include <sys/module.h>
    #include <sys/smp.h>
    
    #include <vm/vm.h>
    #include <vm/pmap.h>
    #include <vm/vm_extern.h>
    
    #include <machine/pvclock.h>
    #include <x86/kvm.h>
    
    #include "clock_if.h"
    
    #define KVM_CLOCK_DEVNAME               "kvmclock"
    /*
     * Note: Chosen to be (1) above HPET's value (always 950), (2) above the TSC's
     * default value of 800, and (3) below the TSC's value when it supports the
     * "Invariant TSC" feature and is believed to be synchronized across all CPUs.
     */
    #define KVM_CLOCK_TC_QUALITY            975
    
    struct kvm_clock_softc {
            struct pvclock                   pvc;
            struct pvclock_wall_clock        wc;
            struct pvclock_vcpu_time_info   *timeinfos;
            u_int                            msr_tc;
            u_int                            msr_wc;
    };
    
    static devclass_t       kvm_clock_devclass;
    
    static struct pvclock_wall_clock *kvm_clock_get_wallclock(void *arg);
    static void     kvm_clock_system_time_enable(struct kvm_clock_softc *sc);
    static void     kvm_clock_system_time_enable_pcpu(void *arg);
    
    static struct pvclock_wall_clock *
    kvm_clock_get_wallclock(void *arg)
    {
            struct kvm_clock_softc *sc = arg;
    
            wrmsr(sc->msr_wc, vtophys(&sc->wc));
            return (&sc->wc);
    }
    
    static void
    kvm_clock_system_time_enable(struct kvm_clock_softc *sc)
    {
            smp_rendezvous(NULL, kvm_clock_system_time_enable_pcpu, NULL, sc);
    }
    
    static void
    kvm_clock_system_time_enable_pcpu(void *arg)
    {
            struct kvm_clock_softc *sc = arg;
   
           /*
            * See [2]; the lsb of this MSR is the system time enable bit.
            */
           wrmsr(sc->msr_tc, vtophys(&(sc->timeinfos)[curcpu]) | 1);
   }
   
   static void
   kvm_clock_identify(driver_t *driver, device_t parent)
   {
           u_int regs[4];
   
           kvm_cpuid_get_features(regs);
           if ((regs[0] &
               (KVM_FEATURE_CLOCKSOURCE2 | KVM_FEATURE_CLOCKSOURCE)) == 0)
                   return;
           if (device_find_child(parent, KVM_CLOCK_DEVNAME, -1))
                   return;
           BUS_ADD_CHILD(parent, 0, KVM_CLOCK_DEVNAME, 0);
   }
   
   static int
   kvm_clock_probe(device_t dev)
   {
           device_set_desc(dev, "KVM paravirtual clock");
           return (BUS_PROBE_DEFAULT);
   }
   
   static int
   kvm_clock_attach(device_t dev)
   {
           u_int regs[4];
           struct kvm_clock_softc *sc = device_get_softc(dev);
           bool stable_flag_supported;
   
           /* Process KVM "features" CPUID leaf content: */
           kvm_cpuid_get_features(regs);
           if ((regs[0] & KVM_FEATURE_CLOCKSOURCE2) != 0) {
                   sc->msr_tc = KVM_MSR_SYSTEM_TIME_NEW;
                   sc->msr_wc = KVM_MSR_WALL_CLOCK_NEW;
           } else {
                   KASSERT((regs[0] & KVM_FEATURE_CLOCKSOURCE) != 0,
                       ("Clocksource feature flags disappeared since "
                       "kvm_clock_identify: regs[0] %#0x.", regs[0]));
                   sc->msr_tc = KVM_MSR_SYSTEM_TIME;
                   sc->msr_wc = KVM_MSR_WALL_CLOCK;
           }
           stable_flag_supported =
               (regs[0] & KVM_FEATURE_CLOCKSOURCE_STABLE_BIT) != 0;
   
           /* Set up 'struct pvclock_vcpu_time_info' page(s): */
           sc->timeinfos = (struct pvclock_vcpu_time_info *)kmem_malloc(mp_ncpus *
               sizeof(struct pvclock_vcpu_time_info), M_WAITOK | M_ZERO);
           kvm_clock_system_time_enable(sc);
   
           /*
            * Init pvclock; register KVM clock wall clock, register KVM clock
            * timecounter, and set up the requisite infrastructure for vDSO access
            * to this timecounter.
            *     Regarding 'tc_flags': Since the KVM MSR documentation does not
            *     specifically discuss suspend/resume scenarios, conservatively
            *     leave 'TC_FLAGS_SUSPEND_SAFE' cleared and assume that the system
            *     time must be re-inited in such cases.
            */
           sc->pvc.get_wallclock = kvm_clock_get_wallclock;
           sc->pvc.get_wallclock_arg = sc;
           sc->pvc.timeinfos = sc->timeinfos;
           sc->pvc.stable_flag_supported = stable_flag_supported;
           pvclock_init(&sc->pvc, dev, KVM_CLOCK_DEVNAME, KVM_CLOCK_TC_QUALITY, 0);
           return (0);
   }
   
   static int
   kvm_clock_detach(device_t dev)
   {
           struct kvm_clock_softc *sc = device_get_softc(dev);
   
           return (pvclock_destroy(&sc->pvc));
   }
   
   static int
   kvm_clock_suspend(device_t dev)
   {
           return (0);
   }
   
   static int
   kvm_clock_resume(device_t dev)
   {
           /*
            * See note in 'kvm_clock_attach()' regarding 'TC_FLAGS_SUSPEND_SAFE';
            * conservatively assume that the system time must be re-inited in
            * suspend/resume scenarios.
            */
           kvm_clock_system_time_enable(device_get_softc(dev));
           pvclock_resume();
           inittodr(time_second);
           return (0);
   }
   
   static int
   kvm_clock_gettime(device_t dev, struct timespec *ts)
   {
           struct kvm_clock_softc *sc = device_get_softc(dev);
   
           pvclock_gettime(&sc->pvc, ts);
           return (0);
   }
   
   static int
   kvm_clock_settime(device_t dev, struct timespec *ts)
   {
           /*
            * Even though it is not possible to set the KVM clock's wall clock, to
            * avoid the possibility of periodic benign error messages from
            * 'settime_task_func()', report success rather than, e.g., 'ENODEV'.
            */
           return (0);
   }
   
   static device_method_t kvm_clock_methods[] = {
           DEVMETHOD(device_identify,      kvm_clock_identify),
           DEVMETHOD(device_probe,         kvm_clock_probe),
           DEVMETHOD(device_attach,        kvm_clock_attach),
           DEVMETHOD(device_detach,        kvm_clock_detach),
           DEVMETHOD(device_suspend,       kvm_clock_suspend),
           DEVMETHOD(device_resume,        kvm_clock_resume),
           /* clock interface */
           DEVMETHOD(clock_gettime,        kvm_clock_gettime),
           DEVMETHOD(clock_settime,        kvm_clock_settime),
   
           DEVMETHOD_END
   };
   
   static driver_t kvm_clock_driver = {
           KVM_CLOCK_DEVNAME,
           kvm_clock_methods,
           sizeof(struct kvm_clock_softc),
   };
   
   DRIVER_MODULE(kvm_clock, nexus, kvm_clock_driver, kvm_clock_devclass, 0, 0);

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