xtensa: fix secondary core boot in SMP

There are multiple factors adding to the issue in different
configurations:

- commit 17290231df16eeee ("xtensa: add fixup for double exception raised
in window overflow") added function window_overflow_restore_a0_fixup to
double exception vector overlapping reset vector location of secondary
processor cores.
- on MMUv2 cores RESET_VECTOR1_VADDR may point to uncached kernel memory
making code overlapping depend on cache type and size, so that without
cache or with WT cache reset vector code overwrites double exception
code, making issue even harder to detect.
- on MMUv3 cores RESET_VECTOR1_VADDR may point to unmapped area, as
MMUv3 cores change virtual address map to match MMUv2 layout, but
reset vector virtual address is given for the original MMUv3 mapping.
- physical memory region of the secondary reset vector is not reserved
in the physical memory map, and thus may be allocated and overwritten
at arbitrary moment.

Fix it as follows:

- move window_overflow_restore_a0_fixup code to .text section.
- define RESET_VECTOR1_VADDR so that it points to reset vector in the
cacheable MMUv2 map for cores with MMU.
- reserve reset vector region in the physical memory map. Drop separate
literal section and build mxhead.S with text section literals.

Cc: <[e-mail]>
Signed-off-by: Max Filippov <[e-mail]>

arch/xtensa/include/asm/vectors.h

···
   #define LOAD_MEMORY_ADDRESS		0xD0003000
 #endif
 
+#define RESET_VECTOR1_VADDR		(VIRTUAL_MEMORY_ADDRESS + \
+					 XCHAL_RESET_VECTOR1_PADDR)
+
 #else /* !defined(CONFIG_MMU) */
   /* MMU Not being used - Virtual == Physical */
 
···
   /* Loaded just above possibly live vectors */
   #define LOAD_MEMORY_ADDRESS		(PLATFORM_DEFAULT_MEM_START + 0x3000)
 
+#define RESET_VECTOR1_VADDR		(XCHAL_RESET_VECTOR1_VADDR)
+
 #endif /* CONFIG_MMU */
 
 #define XC_VADDR(offset)		(VIRTUAL_MEMORY_ADDRESS  + offset)
···
 #define RESET_VECTOR_VECOFS		(XCHAL_RESET_VECTOR_VADDR - \
 						VECBASE_RESET_VADDR)
 #define RESET_VECTOR_VADDR		XC_VADDR(RESET_VECTOR_VECOFS)
-
-#define RESET_VECTOR1_VECOFS		(XCHAL_RESET_VECTOR1_VADDR - \
-						VECBASE_RESET_VADDR)
-#define RESET_VECTOR1_VADDR		XC_VADDR(RESET_VECTOR1_VECOFS)
 
 #if defined(XCHAL_HAVE_VECBASE) && XCHAL_HAVE_VECBASE
 

arch/xtensa/kernel/Makefile

···
 obj-$(CONFIG_XTENSA_VARIANT_HAVE_PERF_EVENTS) += perf_event.o
 
 AFLAGS_head.o += -mtext-section-literals
+AFLAGS_mxhead.o += -mtext-section-literals
 
 # In the Xtensa architecture, assembly generates literals which must always
 # precede the L32R instruction with a relative offset less than 256 kB.

arch/xtensa/kernel/setup.c

···
 extern char _Level6InterruptVector_text_start;
 extern char _Level6InterruptVector_text_end;
 #endif
-
+#ifdef CONFIG_SMP
+extern char _SecondaryResetVector_text_start;
+extern char _SecondaryResetVector_text_end;
+#endif
 
 
 #ifdef CONFIG_S32C1I_SELFTEST
···
 		    __pa(&_Level6InterruptVector_text_end), 0);
 #endif
 
+#ifdef CONFIG_SMP
+	mem_reserve(__pa(&_SecondaryResetVector_text_start),
+		    __pa(&_SecondaryResetVector_text_end), 0);
+#endif
 	parse_early_param();
 	bootmem_init();
 

arch/xtensa/kernel/vectors.S

···
 
 ENDPROC(_DoubleExceptionVector)
 
+	.end literal_prefix
+
+	.text
 /*
  * Fixup handler for TLB miss in double exception handler for window owerflow.
  * We get here with windowbase set to the window that was being spilled and
···
 
 ENDPROC(window_overflow_restore_a0_fixup)
 
-	.end literal_prefix
 /*
  * Debug interrupt vector
  *

arch/xtensa/kernel/vmlinux.lds.S

···
     RELOCATE_ENTRY(_DebugInterruptVector_text,
 		   .DebugInterruptVector.text);
 #if defined(CONFIG_SMP)
-    RELOCATE_ENTRY(_SecondaryResetVector_literal,
-		   .SecondaryResetVector.literal);
     RELOCATE_ENTRY(_SecondaryResetVector_text,
 		   .SecondaryResetVector.text);
 #endif
···
 
 #if defined(CONFIG_SMP)
 
-  SECTION_VECTOR (_SecondaryResetVector_literal,
-		  .SecondaryResetVector.literal,
-		  RESET_VECTOR1_VADDR - 4,
-		  SIZEOF(.DoubleExceptionVector.text),
-		  .DoubleExceptionVector.text)
-
   SECTION_VECTOR (_SecondaryResetVector_text,
 		  .SecondaryResetVector.text,
 		  RESET_VECTOR1_VADDR,
-		  4,
-		  .SecondaryResetVector.literal)
+		  SIZEOF(.DoubleExceptionVector.text),
+		  .DoubleExceptionVector.text)
 
   . = LOADADDR(.SecondaryResetVector.text)+SIZEOF(.SecondaryResetVector.text);