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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
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LeoBras authored and mpe committed Jun 2, 2020
1 parent 783a015 commit b664db8
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Showing 5 changed files with 98 additions and 11 deletions.
2 changes: 2 additions & 0 deletions arch/powerpc/include/asm/paca.h
Original file line number Diff line number Diff line change
Expand Up @@ -29,6 +29,7 @@
#include <asm/hmi.h>
#include <asm/cpuidle.h>
#include <asm/atomic.h>
#include <asm/rtas-types.h>

#include <asm-generic/mmiowb_types.h>

Expand Down Expand Up @@ -256,6 +257,7 @@ struct paca_struct {
u64 l1d_flush_size;
#endif
#ifdef CONFIG_PPC_PSERIES
struct rtas_args *rtas_args_reentrant;
u8 *mce_data_buf; /* buffer to hold per cpu rtas errlog */
#endif /* CONFIG_PPC_PSERIES */

Expand Down
1 change: 1 addition & 0 deletions arch/powerpc/include/asm/rtas.h
Original file line number Diff line number Diff line change
Expand Up @@ -236,6 +236,7 @@ extern struct rtas_t rtas;
extern int rtas_token(const char *service);
extern int rtas_service_present(const char *service);
extern int rtas_call(int token, int, int, int *, ...);
int rtas_call_reentrant(int token, int nargs, int nret, int *outputs, ...);
void rtas_call_unlocked(struct rtas_args *args, int token, int nargs,
int nret, ...);
extern void __noreturn rtas_restart(char *cmd);
Expand Down
32 changes: 32 additions & 0 deletions arch/powerpc/kernel/paca.c
Original file line number Diff line number Diff line change
Expand Up @@ -16,6 +16,7 @@
#include <asm/kexec.h>
#include <asm/svm.h>
#include <asm/ultravisor.h>
#include <asm/rtas.h>

#include "setup.h"

Expand Down Expand Up @@ -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.
Expand Down Expand Up @@ -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 */
Expand Down Expand Up @@ -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);
}
Expand Down
52 changes: 52 additions & 0 deletions arch/powerpc/kernel/rtas.c
Original file line number Diff line number Diff line change
Expand Up @@ -41,6 +41,7 @@
#include <asm/time.h>
#include <asm/mmu.h>
#include <asm/topology.h>
#include <asm/paca.h>

/* This is here deliberately so it's only used in this file */
void enter_rtas(unsigned long);
Expand Down Expand Up @@ -1014,6 +1015,57 @@ int rtas_ibm_suspend_me(u64 handle)
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)
{
Expand Down
22 changes: 11 additions & 11 deletions arch/powerpc/sysdev/xics/ics-rtas.c
Original file line number Diff line number Diff line change
Expand Up @@ -50,8 +50,8 @@ static void ics_rtas_unmask_irq(struct irq_data *d)

server = xics_get_irq_server(d->irq, irq_data_get_affinity_mask(d), 0);

call_status = rtas_call(ibm_set_xive, 3, 1, NULL, hw_irq, server,
DEFAULT_PRIORITY);
call_status = rtas_call_reentrant(ibm_set_xive, 3, 1, NULL, hw_irq,
server, DEFAULT_PRIORITY);
if (call_status != 0) {
printk(KERN_ERR
"%s: ibm_set_xive irq %u server %x returned %d\n",
Expand All @@ -60,7 +60,7 @@ static void ics_rtas_unmask_irq(struct irq_data *d)
}

/* Now unmask the interrupt (often a no-op) */
call_status = rtas_call(ibm_int_on, 1, 1, NULL, hw_irq);
call_status = rtas_call_reentrant(ibm_int_on, 1, 1, NULL, hw_irq);
if (call_status != 0) {
printk(KERN_ERR "%s: ibm_int_on irq=%u returned %d\n",
__func__, hw_irq, call_status);
Expand Down Expand Up @@ -91,16 +91,16 @@ static void ics_rtas_mask_real_irq(unsigned int hw_irq)
if (hw_irq == XICS_IPI)
return;

call_status = rtas_call(ibm_int_off, 1, 1, NULL, hw_irq);
call_status = rtas_call_reentrant(ibm_int_off, 1, 1, NULL, hw_irq);
if (call_status != 0) {
printk(KERN_ERR "%s: ibm_int_off irq=%u returned %d\n",
__func__, hw_irq, call_status);
return;
}

/* Have to set XIVE to 0xff to be able to remove a slot */
call_status = rtas_call(ibm_set_xive, 3, 1, NULL, hw_irq,
xics_default_server, 0xff);
call_status = rtas_call_reentrant(ibm_set_xive, 3, 1, NULL, hw_irq,
xics_default_server, 0xff);
if (call_status != 0) {
printk(KERN_ERR "%s: ibm_set_xive(0xff) irq=%u returned %d\n",
__func__, hw_irq, call_status);
Expand Down Expand Up @@ -131,7 +131,7 @@ static int ics_rtas_set_affinity(struct irq_data *d,
if (hw_irq == XICS_IPI || hw_irq == XICS_IRQ_SPURIOUS)
return -1;

status = rtas_call(ibm_get_xive, 1, 3, xics_status, hw_irq);
status = rtas_call_reentrant(ibm_get_xive, 1, 3, xics_status, hw_irq);

if (status) {
printk(KERN_ERR "%s: ibm,get-xive irq=%u returns %d\n",
Expand All @@ -146,8 +146,8 @@ static int ics_rtas_set_affinity(struct irq_data *d,
return -1;
}

status = rtas_call(ibm_set_xive, 3, 1, NULL,
hw_irq, irq_server, xics_status[1]);
status = rtas_call_reentrant(ibm_set_xive, 3, 1, NULL,
hw_irq, irq_server, xics_status[1]);

if (status) {
printk(KERN_ERR "%s: ibm,set-xive irq=%u returns %d\n",
Expand Down Expand Up @@ -179,7 +179,7 @@ static int ics_rtas_map(struct ics *ics, unsigned int virq)
return -EINVAL;

/* Check if RTAS knows about this interrupt */
rc = rtas_call(ibm_get_xive, 1, 3, status, hw_irq);
rc = rtas_call_reentrant(ibm_get_xive, 1, 3, status, hw_irq);
if (rc)
return -ENXIO;

Expand All @@ -198,7 +198,7 @@ static long ics_rtas_get_server(struct ics *ics, unsigned long vec)
{
int rc, status[2];

rc = rtas_call(ibm_get_xive, 1, 3, status, vec);
rc = rtas_call_reentrant(ibm_get_xive, 1, 3, status, vec);
if (rc)
return -1;
return status[0];
Expand Down

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