Re: [PATCH 2/3] gdbstub: implement NOIRQ support for single step on KVM

["Alex Bennée" <alex.bennee@linaro.org>]

Maxim Levitsky <mlevitsk@redhat.com> writes:

> Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
> ---
>  accel/kvm/kvm-all.c  | 25 ++++++++++++++++++
>  gdbstub.c            | 60 ++++++++++++++++++++++++++++++++++++--------
>  include/sysemu/kvm.h | 13 ++++++++++
>  3 files changed, 88 insertions(+), 10 deletions(-)
>
> diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
> index 6b187e9c96..e141260796 100644
> --- a/accel/kvm/kvm-all.c
> +++ b/accel/kvm/kvm-all.c
> @@ -169,6 +169,8 @@ bool kvm_vm_attributes_allowed;
>  bool kvm_direct_msi_allowed;
>  bool kvm_ioeventfd_any_length_allowed;
>  bool kvm_msi_use_devid;
> +bool kvm_has_guest_debug;
> +int kvm_sstep_flags;
>  static bool kvm_immediate_exit;
>  static hwaddr kvm_max_slot_size = ~0;
>  
> @@ -2559,6 +2561,25 @@ static int kvm_init(MachineState *ms)
>      kvm_sregs2 =
>          (kvm_check_extension(s, KVM_CAP_SREGS2) > 0);
>  
> +    kvm_has_guest_debug =
> +        (kvm_check_extension(s, KVM_CAP_SET_GUEST_DEBUG) > 0);
> +
> +    kvm_sstep_flags = 0;
> +
> +    if (kvm_has_guest_debug) {
> +        /* Assume that single stepping is supported */
> +        kvm_sstep_flags = SSTEP_ENABLE;
> +
> +        int guest_debug_flags =
> +            kvm_check_extension(s, KVM_CAP_SET_GUEST_DEBUG2);
> +
> +        if (guest_debug_flags > 0) {
> +            if (guest_debug_flags & KVM_GUESTDBG_BLOCKIRQ) {
> +                kvm_sstep_flags |= SSTEP_NOIRQ;
> +            }
> +        }
> +    }
> +
>      kvm_state = s;
>  
>      ret = kvm_arch_init(ms, s);
> @@ -3188,6 +3209,10 @@ int kvm_update_guest_debug(CPUState *cpu, unsigned long reinject_trap)
>  
>      if (cpu->singlestep_enabled) {
>          data.dbg.control |= KVM_GUESTDBG_ENABLE | KVM_GUESTDBG_SINGLESTEP;
> +
> +        if (cpu->singlestep_enabled & SSTEP_NOIRQ) {
> +            data.dbg.control |= KVM_GUESTDBG_BLOCKIRQ;
> +        }
>      }
>      kvm_arch_update_guest_debug(cpu, &data.dbg);
>  
> diff --git a/gdbstub.c b/gdbstub.c
> index 5d8e6ae3cd..48bb803bae 100644
> --- a/gdbstub.c
> +++ b/gdbstub.c
> @@ -368,12 +368,11 @@ typedef struct GDBState {
>      gdb_syscall_complete_cb current_syscall_cb;
>      GString *str_buf;
>      GByteArray *mem_buf;
> +    int sstep_flags;
> +    int supported_sstep_flags;
>  } GDBState;
>  
> -/* By default use no IRQs and no timers while single stepping so as to
> - * make single stepping like an ICE HW step.
> - */
> -static int sstep_flags = SSTEP_ENABLE|SSTEP_NOIRQ|SSTEP_NOTIMER;
> +static GDBState gdbserver_state;
>  
>  /* Retrieves flags for single step mode. */
>  static int get_sstep_flags(void)
> @@ -385,11 +384,10 @@ static int get_sstep_flags(void)
>      if (replay_mode != REPLAY_MODE_NONE) {
>          return SSTEP_ENABLE;
>      } else {
> -        return sstep_flags;
> +        return gdbserver_state.sstep_flags;
>      }
>  }
>  
> -static GDBState gdbserver_state;
>  
>  static void init_gdbserver_state(void)
>  {
> @@ -399,6 +397,23 @@ static void init_gdbserver_state(void)
>      gdbserver_state.str_buf = g_string_new(NULL);
>      gdbserver_state.mem_buf = g_byte_array_sized_new(MAX_PACKET_LENGTH);
>      gdbserver_state.last_packet = g_byte_array_sized_new(MAX_PACKET_LENGTH + 4);
> +
> +
> +    if (kvm_enabled()) {
> +        gdbserver_state.supported_sstep_flags = kvm_get_supported_sstep_flags();
> +    } else {
> +        gdbserver_state.supported_sstep_flags =
> +            SSTEP_ENABLE | SSTEP_NOIRQ | SSTEP_NOTIMER;
> +    }

This fails to build:

o -c ../../gdbstub.c
../../gdbstub.c: In function ‘init_gdbserver_state’:
../../gdbstub.c:403:49: error: implicit declaration of function ‘kvm_get_supported_sstep_flags’ [-Werror=implicit-function-declaration]
  403 |         gdbserver_state.supported_sstep_flags = kvm_get_supported_sstep_flags();
      |                                                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
../../gdbstub.c:403:49: error: nested extern declaration of ‘kvm_get_supported_sstep_flags’ [-Werror=nested-externs]
../../gdbstub.c: In function ‘gdbserver_start’:
../../gdbstub.c:3531:27: error: implicit declaration of function ‘kvm_supports_guest_debug’; did you mean ‘kvm_update_guest_debug’? [-Werror=implicit-function-declaration]
 3531 |     if (kvm_enabled() && !kvm_supports_guest_debug()) {
      |                           ^~~~~~~~~~~~~~~~~~~~~~~~
      |                           kvm_update_guest_debug
../../gdbstub.c:3531:27: error: nested extern declaration of ‘kvm_supports_guest_debug’ [-Werror=nested-externs]
cc1: all warnings being treated as errors

In fact looking back I can see I mentioned this last time:

  Subject: Re: [PATCH 2/2] gdbstub: implement NOIRQ support for single step on
   KVM, when kvm's KVM_GUESTDBG_BLOCKIRQ debug flag is supported.
  Date: Mon, 19 Apr 2021 17:29:25 +0100
  In-reply-to: <20210401144152.1031282-3-mlevitsk@redhat.com>
  Message-ID: <871rb69qqk.fsf@linaro.org>

Please in future could you include a revision number for your spin and
mention bellow the --- what changes have been made since the last
posting.


-- 
Alex Bennée