Revert "powerpc/rtas: Implement reentrant rtas call"

At the time this was submitted by Leonardo, I confirmed -- or thought
I had confirmed -- with PowerVM partition firmware development that
the following RTAS functions:

- ibm,get-xive
- ibm,int-off
- ibm,int-on
- ibm,set-xive

were safe to call on multiple CPUs simultaneously, not only with
respect to themselves as indicated by PAPR, but with arbitrary other
RTAS calls:

https://lore.kernel.org/linuxppc-dev/[e-mail]/

Recent discussion with firmware development makes it clear that this
is not true, and that the code in commit b664db8e3f97 ("powerpc/rtas:
Implement reentrant rtas call") is unsafe, likely explaining several
strange bugs we've seen in internal testing involving DLPAR and
LPM. These scenarios use ibm,configure-connector, whose internal state
can be corrupted by the concurrent use of the "reentrant" functions,
leading to symptoms like endless busy statuses from RTAS.

Fixes: b664db8e3f97 ("powerpc/rtas: Implement reentrant rtas call")
Cc: [e-mail] # v5.8+
Signed-off-by: Nathan Lynch <[e-mail]>
Reviewed-by: Laurent Dufour <[e-mail]>
Signed-off-by: Michael Ellerman <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

arch/powerpc/include/asm/paca.h

···
 	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

···
 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

···
 #include <asm/kexec.h>
 #include <asm/svm.h>
 #include <asm/ultravisor.h>
-#include <asm/rtas.h>
 
 #include "setup.h"
 
···
 }
 #endif /* CONFIG_PPC_64S_HASH_MMU */
 
-#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.
···
 #ifdef CONFIG_PPC_BOOK3E
 	/* 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
 }
 
···
 #endif
 #ifdef CONFIG_PPC_64S_HASH_MMU
 	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

···
 #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);
···
 	if (fwrc)
 		pr_err("ibm,activate-firmware failed (%i)\n", fwrc);
 }
-
-#ifdef CONFIG_PPC_PSERIES
-/**
- * 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;
-}
-
-#endif /* CONFIG_PPC_PSERIES */
 
 /**
  * get_pseries_errorlog() - Find a specific pseries error log in an RTAS

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

···
 
 	server = xics_get_irq_server(d->irq, irq_data_get_affinity_mask(d), 0);
 
-	call_status = rtas_call_reentrant(ibm_set_xive, 3, 1, NULL, hw_irq,
-					  server, DEFAULT_PRIORITY);
+	call_status = rtas_call(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",
···
 	}
 
 	/* Now unmask the interrupt (often a no-op) */
-	call_status = rtas_call_reentrant(ibm_int_on, 1, 1, NULL, hw_irq);
+	call_status = rtas_call(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);
···
 	if (hw_irq == XICS_IPI)
 		return;
 
-	call_status = rtas_call_reentrant(ibm_int_off, 1, 1, NULL, hw_irq);
+	call_status = rtas_call(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);
···
 	}
 
 	/* Have to set XIVE to 0xff to be able to remove a slot */
-	call_status = rtas_call_reentrant(ibm_set_xive, 3, 1, NULL, hw_irq,
-					  xics_default_server, 0xff);
+	call_status = rtas_call(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);
···
 	if (hw_irq == XICS_IPI || hw_irq == XICS_IRQ_SPURIOUS)
 		return -1;
 
-	status = rtas_call_reentrant(ibm_get_xive, 1, 3, xics_status, hw_irq);
+	status = rtas_call(ibm_get_xive, 1, 3, xics_status, hw_irq);
 
 	if (status) {
 		printk(KERN_ERR "%s: ibm,get-xive irq=%u returns %d\n",
···
 	pr_debug("%s: irq %d [hw 0x%x] server: 0x%x\n", __func__, d->irq,
 		 hw_irq, irq_server);
 
-	status = rtas_call_reentrant(ibm_set_xive, 3, 1, NULL,
-				     hw_irq, irq_server, xics_status[1]);
+	status = rtas_call(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",
···
 		return -EINVAL;
 
 	/* Check if RTAS knows about this interrupt */
-	rc = rtas_call_reentrant(ibm_get_xive, 1, 3, status, hw_irq);
+	rc = rtas_call(ibm_get_xive, 1, 3, status, hw_irq);
 	if (rc)
 		return -ENXIO;
 
···
 {
 	int rc, status[2];
 
-	rc = rtas_call_reentrant(ibm_get_xive, 1, 3, status, vec);
+	rc = rtas_call(ibm_get_xive, 1, 3, status, vec);
 	if (rc)
 		return -1;
 	return status[0];