[PATCH v3 2/5] powerpc/rtas: Allocate ibm,errinjct buffer below RTAS limit

[Narayana Murty N <nnmlinux@linux.ibm.com>]

ibm,errinjct requires a caller-provided work buffer whose physical
address is passed to RTAS firmware.

A static C array such as:

  char rtas_errinjct_buf[1024] __aligned(SZ_1K);

only guarantees alignment, not physical placement.  If the array lands
above the RTAS-safe range (RTAS_INSTANTIATE_MAX, 1 GB) or above 4 GB,
RTAS receives a truncated or invalid address and the injection call
will fail silently or corrupt memory.

Instead, introduce rtas_errinjct_buf as a global unsigned long storing
the physical address allocated during rtas_initialize() using
memblock_phys_alloc_range() with the same rtas_region upper bound used
for rtas_rmo_buf.  This matches the existing placement model for
RTAS-accessible buffers and guarantees the physical address fits in 32
bits.

  Usage:
    void *buf    = __va(rtas_errinjct_buf);       /* kernel VA to fill */
    u32  buf_phys = lower_32_bits(rtas_errinjct_buf); /* PA for RTAS */

Always check upper_32_bits(rtas_errinjct_buf) == 0 before passing the
lower 32 bits to RTAS.

Add rtas_errinjct_mutex to serialise the complete open-session /
inject / close-session firmware call sequence.  A mutex is required
because the sequence involves multiple rtas_call() invocations with
possible busy/extended-delay retries that may sleep.

Signed-off-by: Narayana Murty N <nnmlinux@linux.ibm.com>
---
 arch/powerpc/include/asm/rtas.h | 26 ++++++++++++++++++++++++++
 arch/powerpc/kernel/rtas.c      | 17 +++++++++++++++++
 2 files changed, 43 insertions(+)

diff --git a/arch/powerpc/include/asm/rtas.h b/arch/powerpc/include/asm/rtas.h
index d046bbd5017d..59e3c1296018 100644
--- a/arch/powerpc/include/asm/rtas.h
+++ b/arch/powerpc/include/asm/rtas.h
@@ -4,6 +4,7 @@
 #ifdef __KERNEL__
 
 #include <linux/mutex.h>
+#include <linux/sizes.h>
 #include <linux/spinlock.h>
 #include <asm/page.h>
 #include <asm/rtas-types.h>
@@ -519,6 +520,31 @@ int rtas_get_error_log_max(void);
 extern spinlock_t rtas_data_buf_lock;
 extern char rtas_data_buf[RTAS_DATA_BUF_SIZE];
 
+/*
+ * RTAS error-injection work buffer.
+ *
+ * ibm,errinjct requires a caller-provided work buffer whose physical
+ * address is passed to firmware.  A static C array only guarantees
+ * alignment, not physical placement; if it lands above the RTAS-safe
+ * range or above 4 GB, RTAS receives a truncated or bogus address.
+ *
+ * rtas_errinjct_buf stores the physical address allocated during
+ * rtas_initialize() using memblock_phys_alloc_range() with the same
+ * rtas_region upper bound used for rtas_rmo_buf, matching the existing
+ * placement model for RTAS-accessible buffers.
+ *
+ * Use __va(rtas_errinjct_buf) to obtain the kernel virtual address for
+ * filling the buffer, and lower_32_bits(rtas_errinjct_buf) to pass the
+ * physical address to RTAS (after checking upper_32_bits() == 0).
+ *
+ * rtas_errinjct_mutex must be held across the complete
+ * ibm,open-errinjct / ibm,errinjct / ibm,close-errinjct sequence.
+ */
+#define RTAS_ERRINJCT_BUF_SIZE	SZ_1K
+
+extern unsigned long rtas_errinjct_buf;
+extern struct mutex rtas_errinjct_mutex;
+
 /* RMO buffer reserved for user-space RTAS use */
 extern unsigned long rtas_rmo_buf;
 
diff --git a/arch/powerpc/kernel/rtas.c b/arch/powerpc/kernel/rtas.c
index 27d53f34494d..7883f973e8c9 100644
--- a/arch/powerpc/kernel/rtas.c
+++ b/arch/powerpc/kernel/rtas.c
@@ -769,6 +769,17 @@ EXPORT_SYMBOL_GPL(rtas_data_buf);
 
 unsigned long rtas_rmo_buf;
 
+/*
+ * Physical address of the ibm,errinjct work buffer.  Allocated during
+ * rtas_initialize() using memblock_phys_alloc_range() below rtas_region
+ * so the address fits in 32 bits and is safe to pass to RTAS firmware.
+ */
+unsigned long rtas_errinjct_buf;
+EXPORT_SYMBOL_GPL(rtas_errinjct_buf);
+
+DEFINE_MUTEX(rtas_errinjct_mutex);
+EXPORT_SYMBOL_GPL(rtas_errinjct_mutex);
+
 /*
  * If non-NULL, this gets called when the kernel terminates.
  * This is done like this so rtas_flash can be a module.
@@ -2109,6 +2120,12 @@ void __init rtas_initialize(void)
 		panic("ERROR: RTAS: Failed to allocate %lx bytes below %pa\n",
 		      PAGE_SIZE, &rtas_region);
 
+	rtas_errinjct_buf = memblock_phys_alloc_range(RTAS_ERRINJCT_BUF_SIZE,
+						      SZ_1K, 0, rtas_region);
+	if (!rtas_errinjct_buf)
+		panic("ERROR: RTAS: Failed to allocate %lu bytes below %pa\n",
+		      (unsigned long)RTAS_ERRINJCT_BUF_SIZE, &rtas_region);
+
 	rtas_work_area_reserve_arena(rtas_region);
 }
 
-- 
2.54.0