Commit b664db8e authored by Leonardo Bras's avatar Leonardo Bras Committed by Michael Ellerman
Browse files

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: default avatarLeonardo Bras <leobras.c@gmail.com>
[mpe: Move under #ifdef PSERIES to avoid build breakage]
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200518234245.200672-3-leobras.c@gmail.com
parent 783a015b

arch/powerpc/include/asm/paca.h

+2 −0
Original line number Diff line number Diff line
@@ -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>
@@ -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 */

arch/powerpc/include/asm/rtas.h

+1 −0
Original line number Diff line number Diff line
@@ -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);

arch/powerpc/kernel/paca.c

+32 −0
Original line number Diff line number Diff line
@@ -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);

}

arch/powerpc/kernel/rtas.c

+52 −0
Original line number Diff line number Diff line
@@ -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);
@@ -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)

{

arch/powerpc/sysdev/xics/ics-rtas.c

+11 −11
Original line number Diff line number Diff line
@@ -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",
@@ -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);
@@ -91,7 +91,7 @@ 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);
@@ -99,7 +99,7 @@ static void ics_rtas_mask_real_irq(unsigned int hw_irq) 
	}



	/* 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,

	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",
@@ -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",
@@ -146,7 +146,7 @@ static int ics_rtas_set_affinity(struct irq_data *d, 
		return -1;

	}



	status = rtas_call(ibm_set_xive, 3, 1, NULL,

	status = rtas_call_reentrant(ibm_set_xive, 3, 1, NULL,

				     hw_irq, irq_server, xics_status[1]);



	if (status) {
@@ -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;
@@ -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];