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powerpc/rtas: Implement reentrant rtas call

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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 <leobras.c@gmail.com>
[mpe: Move under #ifdef PSERIES to avoid build breakage]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200518234245.200672-3-leobras.c@gmail.com
This commit is contained in:
Leonardo Bras
2020-05-18 20:42:45 -03:00
committed by Michael Ellerman
parent 783a015b74
commit b664db8e3f
5 changed files with 98 additions and 11 deletions
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32
arch/powerpc/kernel/paca.c
View File

@@ -16,6 +16,7 @@
#include <asm/kexec.h>
#include <asm/svm.h>
#include <asm/ultravisor.h>
#include <asm/rtas.h>
#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);
}