linux-kernel - [PATCH 1/2] MIPS: Allow vectored interrupt handler to reside everywhere for 64bit

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Date: Thu, 21 Dec 2023 13:54:03 +0100
From: Thomas Bogendoerfer <tsbogend@...ha.franken.de>
To: linux-mips@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH 1/2] MIPS: Allow vectored interrupt handler to reside everywhere for 64bit

Setting up vector interrupts worked only with handlers, which resided
in CKSEG0 space. This limits the kernel placement for 64bit platforms.
By patching in the offset into vi_handlers[] instead of the full
handler address, the vectored exception handler can load the
address by itself and jump to it.

Signed-off-by: Thomas Bogendoerfer <tsbogend@...ha.franken.de>
---
 arch/mips/kernel/genex.S | 8 ++++----
 arch/mips/kernel/traps.c | 9 +++------
 2 files changed, 7 insertions(+), 10 deletions(-)

diff --git a/arch/mips/kernel/genex.S b/arch/mips/kernel/genex.S
index b6de8e88c1bd..a572ce36a24f 100644
--- a/arch/mips/kernel/genex.S
+++ b/arch/mips/kernel/genex.S
@@ -272,18 +272,17 @@ NESTED(except_vec_vi, 0, sp)
 	.set	push
 	.set	noreorder
 	PTR_LA	v1, except_vec_vi_handler
-FEXPORT(except_vec_vi_lui)
-	lui	v0, 0		/* Patched */
 	jr	v1
 FEXPORT(except_vec_vi_ori)
-	 ori	v0, 0		/* Patched */
+	 ori	v0, zero, 0		/* Offset in vi_handlers[] */
 	.set	pop
 	END(except_vec_vi)
 EXPORT(except_vec_vi_end)
 
 /*
  * Common Vectored Interrupt code
- * Complete the register saves and invoke the handler which is passed in $v0
+ * Complete the register saves and invoke the handler, $v0 holds
+ * offset into vi_handlers[]
  */
 NESTED(except_vec_vi_handler, 0, sp)
 	SAVE_TEMP
@@ -331,6 +330,7 @@ NESTED(except_vec_vi_handler, 0, sp)
 	/* Save task's sp on IRQ stack so that unwinding can follow it */
 	LONG_S	s1, 0(sp)
 2:
+	PTR_L	v0, vi_handlers(v0)
 	jalr	v0
 
 	/* Restore sp */
diff --git a/arch/mips/kernel/traps.c b/arch/mips/kernel/traps.c
index 246c6a6b0261..d90b18908692 100644
--- a/arch/mips/kernel/traps.c
+++ b/arch/mips/kernel/traps.c
@@ -2091,16 +2091,14 @@ static void *set_vi_srs_handler(int n, vi_handler_t addr, int srs)
 		 * If no shadow set is selected then use the default handler
 		 * that does normal register saving and standard interrupt exit
 		 */
-		extern const u8 except_vec_vi[], except_vec_vi_lui[];
+		extern const u8 except_vec_vi[];
 		extern const u8 except_vec_vi_ori[], except_vec_vi_end[];
 		extern const u8 rollback_except_vec_vi[];
 		const u8 *vec_start = using_rollback_handler() ?
 				      rollback_except_vec_vi : except_vec_vi;
 #if defined(CONFIG_CPU_MICROMIPS) || defined(CONFIG_CPU_BIG_ENDIAN)
-		const int lui_offset = except_vec_vi_lui - vec_start + 2;
 		const int ori_offset = except_vec_vi_ori - vec_start + 2;
 #else
-		const int lui_offset = except_vec_vi_lui - vec_start;
 		const int ori_offset = except_vec_vi_ori - vec_start;
 #endif
 		const int handler_len = except_vec_vi_end - vec_start;
@@ -2119,10 +2117,9 @@ static void *set_vi_srs_handler(int n, vi_handler_t addr, int srs)
 #else
 				handler_len);
 #endif
-		h = (u16 *)(b + lui_offset);
-		*h = (handler >> 16) & 0xffff;
+		/* insert offset into vi_handlers[] */
 		h = (u16 *)(b + ori_offset);
-		*h = (handler & 0xffff);
+		*h = n * sizeof(handler);
 		local_flush_icache_range((unsigned long)b,
 					 (unsigned long)(b+handler_len));
 	}
-- 
2.35.3