Re: [PATCH 4/8] i386: hvf: Implement CPU kick

[Paolo Bonzini]

On 25/06/20 00:58, Roman Bolshakov wrote:
> HVF doesn't have a CPU kick and without it it's not possible to perform
> an action on CPU thread until a VMEXIT happens. The kick is also needed
> for timely interrupt delivery.
> 
> Existing implementation of CPU kick sends SIG_IPI (aka SIGUSR1) to vCPU
> thread, but it's different from what hv_vcpu_interrupt does. The latter
> one results in invocation of mp_cpus_kick() in XNU kernel [1].
> 
> While at it, correct type of hvf_fd to the type of hv_vcpuid_t to avoid
> compilation warnings.
> 
> 1. https://opensource.apple.com/source/xnu/xnu-6153.81.5/osfmk/i386/mp.c
> 
> Cc: Cameron Esfahani <dirty@apple.com>
> Signed-off-by: Roman Bolshakov <r.bolshakov@yadro.com>
> ---
>  cpus.c                | 13 +++++++++----
>  include/hw/core/cpu.h |  2 +-
>  include/sysemu/hvf.h  |  1 +
>  target/i386/hvf/hvf.c | 11 +++++++++++
>  4 files changed, 22 insertions(+), 5 deletions(-)
> 
> diff --git a/cpus.c b/cpus.c
> index 26709677d3..36f38ce5c8 100644
> --- a/cpus.c
> +++ b/cpus.c
> @@ -1783,10 +1783,15 @@ static void qemu_cpu_kick_thread(CPUState *cpu)
>          return;
>      }
>      cpu->thread_kicked = true;
> -    err = pthread_kill(cpu->thread->thread, SIG_IPI);
> -    if (err && err != ESRCH) {
> -        fprintf(stderr, "qemu:%s: %s", __func__, strerror(err));
> -        exit(1);
> +
> +    if (hvf_enabled()) {
> +        hvf_vcpu_kick(cpu);
> +    } else {
> +        err = pthread_kill(cpu->thread->thread, SIG_IPI);
> +        if (err && err != ESRCH) {
> +            fprintf(stderr, "qemu:%s: %s", __func__, strerror(err));
> +            exit(1);
> +        }
>      }
>  #else /* _WIN32 */
>      if (!qemu_cpu_is_self(cpu)) {
> diff --git a/include/hw/core/cpu.h b/include/hw/core/cpu.h
> index b3f4b79318..288a2bd57e 100644
> --- a/include/hw/core/cpu.h
> +++ b/include/hw/core/cpu.h
> @@ -438,7 +438,7 @@ struct CPUState {
>  
>      struct hax_vcpu_state *hax_vcpu;
>  
> -    int hvf_fd;
> +    unsigned hvf_fd;
>  
>      /* track IOMMUs whose translations we've cached in the TCG TLB */
>      GArray *iommu_notifiers;
> diff --git a/include/sysemu/hvf.h b/include/sysemu/hvf.h
> index 1d40a8ec01..aaa00cbf05 100644
> --- a/include/sysemu/hvf.h
> +++ b/include/sysemu/hvf.h
> @@ -25,6 +25,7 @@ extern bool hvf_allowed;
>  
>  int hvf_init_vcpu(CPUState *);
>  int hvf_vcpu_exec(CPUState *);
> +void hvf_vcpu_kick(CPUState *);
>  void hvf_cpu_synchronize_state(CPUState *);
>  void hvf_cpu_synchronize_post_reset(CPUState *);
>  void hvf_cpu_synchronize_post_init(CPUState *);
> diff --git a/target/i386/hvf/hvf.c b/target/i386/hvf/hvf.c
> index efe9802962..4d254a477a 100644
> --- a/target/i386/hvf/hvf.c
> +++ b/target/i386/hvf/hvf.c
> @@ -966,6 +966,17 @@ int hvf_vcpu_exec(CPUState *cpu)
>      return ret;
>  }
>  
> +void hvf_vcpu_kick(CPUState *cpu)
> +{
> +    hv_return_t err;
> +
> +    err = hv_vcpu_interrupt(&cpu->hvf_fd, 1);
> +    if (err) {
> +        fprintf(stderr, "qemu:%s error %#x\n", __func__, err);
> +        exit(1);
> +    }
> +}
> +
>  bool hvf_allowed;
>  
>  static int hvf_accel_init(MachineState *ms)
> 

The documentation isn't clear on whether hv_vcpu_interrupt is able to
interrupt a *subsequent* hv_vcpu_run, similar to WHPX
WHvCancelRunVirtualProcessor (is it possible to decompile
hv_vcpu_interrupt and see what it does?).  If not, you can reduce a bit
the race window by setting a variable in cpu, like

        atomic_set(&cpu->deadline, 0);
        hv_vcpu_interrupt(...)

and in the vCPU thread

        hv_vcpu_run_until(..., atomic_read(&cpu->deadline));
        atomic_set(&cpu->deadline, HV_DEADLINE_FOREVER);

Paolo