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/875zcy2v8o.fsf@linux.ibm.com/

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: stable@vger.kernel.org # v5.8+
Signed-off-by: Nathan Lynch <nathanl@linux.ibm.com>
Reviewed-by: Laurent Dufour <laurent.dufour@fr.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220907220111.223267-1-nathanl@linux.ibm.com

2 files changed, 0 insertions, 86 deletions

diff --git a/arch/powerpc/kernel/paca.c b/arch/powerpc/kernel/paca.c
index ba593fd60124..dfd097b79160 100644
--- a/arch/powerpc/kernel/paca.c
+++ b/arch/powerpc/kernel/paca.c
@@ -16,7 +16,6 @@
 #include <asm/kexec.h>
 #include <asm/svm.h>
 #include <asm/ultravisor.h>
-#include <asm/rtas.h>
 
 #include "setup.h"
 
@@ -170,30 +169,6 @@ static struct slb_shadow * __init new_slb_shadow(int cpu, unsigned long limit)
 }
 #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.
@@ -232,10 +207,6 @@ void __init initialise_paca(struct paca_struct *new_paca, int cpu)
 	/* 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 */
@@ -308,9 +279,6 @@ void __init allocate_paca(int cpu)
 #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);
 }
 
diff --git a/arch/powerpc/kernel/rtas.c b/arch/powerpc/kernel/rtas.c
index 693133972294..0b8a858aa847 100644
--- a/arch/powerpc/kernel/rtas.c
+++ b/arch/powerpc/kernel/rtas.c
@@ -43,7 +43,6 @@
 #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);
@@ -932,59 +931,6 @@ void rtas_activate_firmware(void)
 		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
  *                          extended event log.