Re: [PATCH v3 01/19] target/ppc: Fix msgsnd for POWER8

[Cédric Le Goater]

On 7/16/24 18:25, Nicholas Piggin wrote:
> POWER8 (ISA v2.07S) introduced the doorbell facility, the msgsnd
> instruction behaved mostly like msgsndp, it was addressed by TIR
> and could only send interrupts between threads on the core.
>
> ISA v3.0 changed msgsnd to be addressed by PIR and can interrupt
> any thread in the system.
>
> msgsnd only implements the v3.0 semantics, which can make
> multi-threaded POWER8 hang when booting Linux (due to IPIs
> failing). This change adds v2.07 semantics.
>
> Signed-off-by: Nicholas Piggin <npiggin@gmail.com>


Reviewed-by: Cédric Le Goater <clg@redhat.com>

Thanks,

C.


> ---
>   target/ppc/excp_helper.c | 74 ++++++++++++++++++++++++----------------
>   1 file changed, 44 insertions(+), 30 deletions(-)
>
> diff --git a/target/ppc/excp_helper.c b/target/ppc/excp_helper.c
> index 0a9e8539a4..5368bf2ff3 100644
> --- a/target/ppc/excp_helper.c
> +++ b/target/ppc/excp_helper.c
> @@ -3007,6 +3007,41 @@ static inline bool dbell_bcast_subproc(target_ulong rb)
>       return (rb & DBELL_BRDCAST_MASK) == DBELL_BRDCAST_SUBPROC;
>   }
>   
> +/*
> + * Send an interrupt to a thread in the same core as env).
> + */
> +static void msgsnd_core_tir(CPUPPCState *env, uint32_t target_tir, int irq)
> +{
> +    PowerPCCPU *cpu = env_archcpu(env);
> +    CPUState *cs = env_cpu(env);
> +    uint32_t nr_threads = cs->nr_threads;
> +
> +    if (!(env->flags & POWERPC_FLAG_SMT_1LPAR)) {
> +        nr_threads = 1; /* msgsndp behaves as 1-thread in LPAR-per-thread 
> mode*/
> +    }
> +
> +    if (target_tir >= nr_threads) {
> +        return;
> +    }
> +
> +    if (nr_threads == 1) {
> +        ppc_set_irq(cpu, irq, 1);
> +    } else {
> +        CPUState *ccs;
> +
> +        /* Does iothread need to be locked for walking CPU list? */
> +        bql_lock();
> +        THREAD_SIBLING_FOREACH(cs, ccs) {
> +            PowerPCCPU *ccpu = POWERPC_CPU(ccs);
> +            if (target_tir == ppc_cpu_tir(ccpu)) {
> +                ppc_set_irq(ccpu, irq, 1);
> +                break;
> +            }
> +        }
> +        bql_unlock();
> +    }
> +}
> +
>   void helper_book3s_msgclr(CPUPPCState *env, target_ulong rb)
>   {
>       if (!dbell_type_server(rb)) {
> @@ -3027,6 +3062,13 @@ void helper_book3s_msgsnd(CPUPPCState *env, target_ulong 
> rb)
>           return;
>       }
>   
> +    /* POWER8 msgsnd is like msgsndp (targets a thread within core) */
> +    if (!(env->insns_flags2 & PPC2_ISA300)) {
> +        msgsnd_core_tir(env, rb & PPC_BITMASK(57, 63), 
> PPC_INTERRUPT_HDOORBELL);
> +        return;
> +    }
> +
> +    /* POWER9 and later msgsnd is a global (targets any thread) */
>       cpu = ppc_get_vcpu_by_pir(pir);
>       if (!cpu) {
>           return;
> @@ -3073,41 +3115,13 @@ void helper_book3s_msgclrp(CPUPPCState *env, 
> target_ulong rb)
>    */
>   void helper_book3s_msgsndp(CPUPPCState *env, target_ulong rb)
>   {
> -    CPUState *cs = env_cpu(env);
> -    PowerPCCPU *cpu = env_archcpu(env);
> -    CPUState *ccs;
> -    uint32_t nr_threads = cs->nr_threads;
> -    int ttir = rb & PPC_BITMASK(57, 63);
> -
>       helper_hfscr_facility_check(env, HFSCR_MSGP, "msgsndp", HFSCR_IC_MSGP);
>   
> -    if (!(env->flags & POWERPC_FLAG_SMT_1LPAR)) {
> -        nr_threads = 1; /* msgsndp behaves as 1-thread in LPAR-per-thread 
> mode*/
> -    }
> -
> -    if (!dbell_type_server(rb) || ttir >= nr_threads) {
> -        return;
> -    }
> -
> -    if (nr_threads == 1) {
> -        ppc_set_irq(cpu, PPC_INTERRUPT_DOORBELL, 1);
> +    if (!dbell_type_server(rb)) {
>           return;
>       }
>   
> -    /* Does iothread need to be locked for walking CPU list? */
> -    bql_lock();
> -    THREAD_SIBLING_FOREACH(cs, ccs) {
> -        PowerPCCPU *ccpu = POWERPC_CPU(ccs);
> -        uint32_t thread_id = ppc_cpu_tir(ccpu);
> -
> -        if (ttir == thread_id) {
> -            ppc_set_irq(ccpu, PPC_INTERRUPT_DOORBELL, 1);
> -            bql_unlock();
> -            return;
> -        }
> -    }
> -
> -    g_assert_not_reached();
> +    msgsnd_core_tir(env, rb & PPC_BITMASK(57, 63), PPC_INTERRUPT_DOORBELL);
>   }
>   #endif /* TARGET_PPC64 */
>