From b664db8e3f976d9233cc9ea5e3f8a8c0bcabeb48 Mon Sep 17 00:00:00 2001 From: Leonardo Bras Date: Mon, 18 May 2020 20:42:45 -0300 Subject: powerpc/rtas: Implement reentrant rtas call Implement rtas_call_reentrant() for reentrant rtas-calls: "ibm,int-on", "ibm,int-off",ibm,get-xive" and "ibm,set-xive". On LoPAPR Version 1.1 (March 24, 2016), from 7.3.10.1 to 7.3.10.4, items 2 and 3 say: 2 - For the PowerPC External Interrupt option: The * call must be reentrant to the number of processors on the platform. 3 - For the PowerPC External Interrupt option: The * argument call buffer for each simultaneous call must be physically unique. So, these rtas-calls can be called in a lockless way, if using a different buffer for each cpu doing such rtas call. For this, it was suggested to add the buffer (struct rtas_args) in the PACA struct, so each cpu can have it's own buffer. The PACA struct received a pointer to rtas buffer, which is allocated in the memory range available to rtas 32-bit. Reentrant rtas calls are useful to avoid deadlocks in crashing, where rtas-calls are needed, but some other thread crashed holding the rtas.lock. This is a backtrace of a deadlock from a kdump testing environment: #0 arch_spin_lock #1 lock_rtas () #2 rtas_call (token=8204, nargs=1, nret=1, outputs=0x0) #3 ics_rtas_mask_real_irq (hw_irq=4100) #4 machine_kexec_mask_interrupts #5 default_machine_crash_shutdown #6 machine_crash_shutdown #7 __crash_kexec #8 crash_kexec #9 oops_end Signed-off-by: Leonardo Bras [mpe: Move under #ifdef PSERIES to avoid build breakage] Signed-off-by: Michael Ellerman Link: https://lore.kernel.org/r/20200518234245.200672-3-leobras.c@gmail.com --- arch/powerpc/kernel/paca.c | 32 ++++++++++++++++++++++++++++ arch/powerpc/kernel/rtas.c | 52 ++++++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 84 insertions(+) (limited to 'arch/powerpc/kernel') diff --git a/arch/powerpc/kernel/paca.c b/arch/powerpc/kernel/paca.c index 3f91ccaa9c74..8d96169c597e 100644 --- a/arch/powerpc/kernel/paca.c +++ b/arch/powerpc/kernel/paca.c @@ -16,6 +16,7 @@ #include #include #include +#include #include "setup.h" @@ -164,6 +165,30 @@ static struct slb_shadow * __init new_slb_shadow(int cpu, unsigned long limit) #endif /* CONFIG_PPC_BOOK3S_64 */ +#ifdef CONFIG_PPC_PSERIES +/** + * new_rtas_args() - Allocates rtas args + * @cpu: CPU number + * @limit: Memory limit for this allocation + * + * Allocates a struct rtas_args and return it's pointer, + * if not in Hypervisor mode + * + * Return: Pointer to allocated rtas_args + * NULL if CPU in Hypervisor Mode + */ +static struct rtas_args * __init new_rtas_args(int cpu, unsigned long limit) +{ + limit = min_t(unsigned long, limit, RTAS_INSTANTIATE_MAX); + + if (early_cpu_has_feature(CPU_FTR_HVMODE)) + return NULL; + + return alloc_paca_data(sizeof(struct rtas_args), L1_CACHE_BYTES, + limit, cpu); +} +#endif /* CONFIG_PPC_PSERIES */ + /* The Paca is an array with one entry per processor. Each contains an * lppaca, which contains the information shared between the * hypervisor and Linux. @@ -202,6 +227,10 @@ void __init __nostackprotector initialise_paca(struct paca_struct *new_paca, int /* For now -- if we have threads this will be adjusted later */ new_paca->tcd_ptr = &new_paca->tcd; #endif + +#ifdef CONFIG_PPC_PSERIES + new_paca->rtas_args_reentrant = NULL; +#endif } /* Put the paca pointer into r13 and SPRG_PACA */ @@ -273,6 +302,9 @@ void __init allocate_paca(int cpu) #endif #ifdef CONFIG_PPC_BOOK3S_64 paca->slb_shadow_ptr = new_slb_shadow(cpu, limit); +#endif +#ifdef CONFIG_PPC_PSERIES + paca->rtas_args_reentrant = new_rtas_args(cpu, limit); #endif paca_struct_size += sizeof(struct paca_struct); } diff --git a/arch/powerpc/kernel/rtas.c b/arch/powerpc/kernel/rtas.c index c5fa251b8950..a09eba03f180 100644 --- a/arch/powerpc/kernel/rtas.c +++ b/arch/powerpc/kernel/rtas.c @@ -41,6 +41,7 @@ #include #include #include +#include /* This is here deliberately so it's only used in this file */ void enter_rtas(unsigned long); @@ -1014,6 +1015,57 @@ out: free_cpumask_var(offline_mask); return atomic_read(&data.error); } + +/** + * rtas_call_reentrant() - Used for reentrant rtas calls + * @token: Token for desired reentrant RTAS call + * @nargs: Number of Input Parameters + * @nret: Number of Output Parameters + * @outputs: Array of outputs + * @...: Inputs for desired RTAS call + * + * According to LoPAR documentation, only "ibm,int-on", "ibm,int-off", + * "ibm,get-xive" and "ibm,set-xive" are currently reentrant. + * Reentrant calls need their own rtas_args buffer, so not using rtas.args, but + * PACA one instead. + * + * Return: -1 on error, + * First output value of RTAS call if (nret > 0), + * 0 otherwise, + */ +int rtas_call_reentrant(int token, int nargs, int nret, int *outputs, ...) +{ + va_list list; + struct rtas_args *args; + unsigned long flags; + int i, ret = 0; + + if (!rtas.entry || token == RTAS_UNKNOWN_SERVICE) + return -1; + + local_irq_save(flags); + preempt_disable(); + + /* We use the per-cpu (PACA) rtas args buffer */ + args = local_paca->rtas_args_reentrant; + + va_start(list, outputs); + va_rtas_call_unlocked(args, token, nargs, nret, list); + va_end(list); + + if (nret > 1 && outputs) + for (i = 0; i < nret - 1; ++i) + outputs[i] = be32_to_cpu(args->rets[i + 1]); + + if (nret > 0) + ret = be32_to_cpu(args->rets[0]); + + local_irq_restore(flags); + preempt_enable(); + + return ret; +} + #else /* CONFIG_PPC_PSERIES */ int rtas_ibm_suspend_me(u64 handle) { -- cgit v1.2.3