[Pdbg] [PATCH v2 22/39] gdbserver: check for attn using the SPATTN register

[Joel Stanley]

On Wed, 20 Apr 2022 at 06:51, Nicholas Piggin <npiggin at gmail.com> wrote:
>
> When POWER9/10 execute an attn instruction, they set a bit in the SPATTN
> register and quiesce the thread.
>
> This bit can be checked to confirm the thread hit an attn instruction,
> rather than assuming a thread was quiesced because of attn. This makes
> the gdb breakpoint code more robust in the presence of other direct
> controls (e.g., host-based direct controls from OPAL).
>
> This change also clears the SPATTN bit which clears the exception
> condition that raises the IPOLL global interrupt. That interrupt seems
> to be involved with the IPOLL interrupt storm and lock-up on POWER9
> (although this does not fix it).
>
> Signed-off-by: Nicholas Piggin <npiggin at gmail.com>
> ---
>  src/pdbgproxy.c | 79 ++++++++++++++++++++++++++++++++++++++++++-------
>  1 file changed, 68 insertions(+), 11 deletions(-)
>
> diff --git a/src/pdbgproxy.c b/src/pdbgproxy.c
> index 23971c25..d7ceac8d 100644
> --- a/src/pdbgproxy.c
> +++ b/src/pdbgproxy.c
> @@ -457,6 +457,59 @@ static void v_contc(uint64_t *stack, void *priv)
>         poll_interval = 1;
>  }
>
> +#define P9_SPATTN_AND  0x20010A98
> +#define P9_SPATTN      0x20010A99
> +
> +#define P10_SPATTN_AND 0x20028498
> +#define P10_SPATTN     0x20028499
> +
> +static bool thread_check_attn(struct pdbg_target *target)
> +{
> +       struct thread *thread = target_to_thread(target);
> +       struct pdbg_target *core;
> +       uint64_t spattn;
> +
> +       if (pdbg_target_compatible(target, "ibm,power8-thread")) {
> +               return true; /* XXX */

I assume this is ok?

Reviewed-by: Joel Stanley <joel at jms.id.au>

> +       } else if (pdbg_target_compatible(target, "ibm,power9-thread")) {
> +               core = pdbg_target_require_parent("core", target);
> +               if (pib_read(core, P9_SPATTN, &spattn)) {
> +                       PR_ERROR("SPATTN read failed\n");
> +                       return false;
> +               }
> +
> +               if (spattn & PPC_BIT(1 + 4*thread->id)) {
> +                       uint64_t mask = ~PPC_BIT(1 + 4*thread->id);
> +
> +                       if (pib_write(core, P9_SPATTN_AND, mask)) {
> +                               PR_ERROR("SPATTN clear failed\n");
> +                               return false;
> +                       }
> +
> +                       return true;
> +               }
> +       } else if (pdbg_target_compatible(target, "ibm,power10-thread")) {
> +               core = pdbg_target_require_parent("core", target);
> +               if (pib_read(core, P10_SPATTN, &spattn)) {
> +                       PR_ERROR("SPATTN read failed\n");
> +                       return false;
> +               }
> +
> +               if (spattn & PPC_BIT(1 + 4*thread->id)) {
> +                       uint64_t mask = ~PPC_BIT(1 + 4*thread->id);
> +
> +                       if (pib_write(core, P10_SPATTN_AND, mask)) {
> +                               PR_ERROR("SPATTN clear failed\n");
> +                               return false;
> +                       }
> +
> +                       return true;
> +               }
> +       }
> +
> +       return false;
> +}
> +
>  static void interrupt(uint64_t *stack, void *priv)
>  {
>         struct thread_state status;
> @@ -477,7 +530,6 @@ static void interrupt(uint64_t *stack, void *priv)
>
>  static void poll(void)
>  {
> -       uint64_t nia;
>         struct thread_state status;
>
>         thread_target->probe(thread_target);
> @@ -495,17 +547,22 @@ static void poll(void)
>
>                 state = IDLE;
>                 poll_interval = VCONT_POLL_DELAY;
> -               if (!(status.active)) {
> -                       PR_ERROR("Thread inactive after trap\n");
> -                       send_response(fd, ERROR(EPERM));
> -                       return;
> -               }
>
> -               /* Restore NIA */
> -               if (thread_getnia(thread_target, &nia))
> -                       PR_ERROR("Error during getnia\n");
> -               if (thread_putnia(thread_target, nia - 4))
> -                       PR_ERROR("Error during putnia\n");
> +               if (thread_check_attn(thread_target)) {
> +                       uint64_t nia;
> +
> +                       if (!(status.active)) {
> +                               PR_ERROR("Thread inactive after trap\n");
> +                               send_response(fd, ERROR(EPERM));
> +                               return;
> +                       }
> +
> +                       /* Restore NIA */
> +                       if (thread_getnia(thread_target, &nia))
> +                               PR_ERROR("Error during getnia\n");
> +                       if (thread_putnia(thread_target, nia - 4))
> +                               PR_ERROR("Error during putnia\n");
> +               }
>                 send_response(fd, TRAP);
>                 break;
>         }
> --
> 2.35.1
>
> --
> Pdbg mailing list
> Pdbg at lists.ozlabs.org
> https://lists.ozlabs.org/listinfo/pdbg