[PATCH v4 01/13] openrisc: use shadow registers to save regs on exception

From: Stafford Horne
Date: Sun Oct 29 2017 - 19:12:03 EST

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From: Stefan Kristiansson <stefan.kristiansson@xxxxxxxxxxxxx>

Previously, the area between 0x0-0x100 have been used as a "scratch"
memory area to temporarily store regs during exception entry. In a
multi-core environment, this will not work.

This change is to use shadow registers for nested context.

Currently only the "critical" temp load/stores are covered, the
EMERGENCY_PRINT ones are left as is (when they are used, it's game over
anyway), they need to be handled as well in the future.

Signed-off-by: Stefan Kristiansson <stefan.kristiansson@xxxxxxxxxxxxx>
Signed-off-by: Stafford Horne <shorne@xxxxxxxxx>
---

Changes since v2
- None

Changes since v1
- Added SMP checks in Kconfig

arch/openrisc/Kconfig | 11 ++++++
arch/openrisc/kernel/head.S | 95 ++++++++++++++++++++++++++++++++-------------
2 files changed, 80 insertions(+), 26 deletions(-)

diff --git a/arch/openrisc/Kconfig b/arch/openrisc/Kconfig
index a0f2e4a323c1..356dd67a86ea 100644
--- a/arch/openrisc/Kconfig
+++ b/arch/openrisc/Kconfig
@@ -124,6 +124,17 @@ config OPENRISC_NO_SPR_SR_DSX
Say N here if you know that your OpenRISC processor has
SPR_SR_DSX bit implemented. Say Y if you are unsure.

+config OPENRISC_HAVE_SHADOW_GPRS
+ bool "Support for shadow gpr files" if !SMP
+ default y if SMP
+ help
+ Say Y here if your OpenRISC processor features shadowed
+ register files. They will in such case be used as a
+ scratch reg storage on exception entry.
+
+ On SMP systems, this feature is mandatory.
+ On a unicore system it's safe to say N here if you are unsure.
+
config CMDLINE
string "Default kernel command string"
default ""
diff --git a/arch/openrisc/kernel/head.S b/arch/openrisc/kernel/head.S
index 1e87913576e3..1e49895408f4 100644
--- a/arch/openrisc/kernel/head.S
+++ b/arch/openrisc/kernel/head.S
@@ -49,9 +49,31 @@

/* ============================================[ tmp store locations ]=== */

+#define SPR_SHADOW_GPR(x) ((x) + SPR_GPR_BASE + 32)
+
/*
* emergency_print temporary stores
*/
+#ifdef CONFIG_OPENRISC_HAVE_SHADOW_GPRS
+#define EMERGENCY_PRINT_STORE_GPR4 l.mtspr r0,r4,SPR_SHADOW_GPR(14)
+#define EMERGENCY_PRINT_LOAD_GPR4 l.mfspr r4,r0,SPR_SHADOW_GPR(14)
+
+#define EMERGENCY_PRINT_STORE_GPR5 l.mtspr r0,r5,SPR_SHADOW_GPR(15)
+#define EMERGENCY_PRINT_LOAD_GPR5 l.mfspr r5,r0,SPR_SHADOW_GPR(15)
+
+#define EMERGENCY_PRINT_STORE_GPR6 l.mtspr r0,r6,SPR_SHADOW_GPR(16)
+#define EMERGENCY_PRINT_LOAD_GPR6 l.mfspr r6,r0,SPR_SHADOW_GPR(16)
+
+#define EMERGENCY_PRINT_STORE_GPR7 l.mtspr r0,r7,SPR_SHADOW_GPR(7)
+#define EMERGENCY_PRINT_LOAD_GPR7 l.mfspr r7,r0,SPR_SHADOW_GPR(7)
+
+#define EMERGENCY_PRINT_STORE_GPR8 l.mtspr r0,r8,SPR_SHADOW_GPR(8)
+#define EMERGENCY_PRINT_LOAD_GPR8 l.mfspr r8,r0,SPR_SHADOW_GPR(8)
+
+#define EMERGENCY_PRINT_STORE_GPR9 l.mtspr r0,r9,SPR_SHADOW_GPR(9)
+#define EMERGENCY_PRINT_LOAD_GPR9 l.mfspr r9,r0,SPR_SHADOW_GPR(9)
+
+#else /* !CONFIG_OPENRISC_HAVE_SHADOW_GPRS */
#define EMERGENCY_PRINT_STORE_GPR4 l.sw 0x20(r0),r4
#define EMERGENCY_PRINT_LOAD_GPR4 l.lwz r4,0x20(r0)

@@ -70,13 +92,28 @@
#define EMERGENCY_PRINT_STORE_GPR9 l.sw 0x34(r0),r9
#define EMERGENCY_PRINT_LOAD_GPR9 l.lwz r9,0x34(r0)

+#endif

/*
* TLB miss handlers temorary stores
*/
-#define EXCEPTION_STORE_GPR9 l.sw 0x10(r0),r9
-#define EXCEPTION_LOAD_GPR9 l.lwz r9,0x10(r0)
+#ifdef CONFIG_OPENRISC_HAVE_SHADOW_GPRS
+#define EXCEPTION_STORE_GPR2 l.mtspr r0,r2,SPR_SHADOW_GPR(2)
+#define EXCEPTION_LOAD_GPR2 l.mfspr r2,r0,SPR_SHADOW_GPR(2)
+
+#define EXCEPTION_STORE_GPR3 l.mtspr r0,r3,SPR_SHADOW_GPR(3)
+#define EXCEPTION_LOAD_GPR3 l.mfspr r3,r0,SPR_SHADOW_GPR(3)

+#define EXCEPTION_STORE_GPR4 l.mtspr r0,r4,SPR_SHADOW_GPR(4)
+#define EXCEPTION_LOAD_GPR4 l.mfspr r4,r0,SPR_SHADOW_GPR(4)
+
+#define EXCEPTION_STORE_GPR5 l.mtspr r0,r5,SPR_SHADOW_GPR(5)
+#define EXCEPTION_LOAD_GPR5 l.mfspr r5,r0,SPR_SHADOW_GPR(5)
+
+#define EXCEPTION_STORE_GPR6 l.mtspr r0,r6,SPR_SHADOW_GPR(6)
+#define EXCEPTION_LOAD_GPR6 l.mfspr r6,r0,SPR_SHADOW_GPR(6)
+
+#else /* !CONFIG_OPENRISC_HAVE_SHADOW_GPRS */
#define EXCEPTION_STORE_GPR2 l.sw 0x64(r0),r2
#define EXCEPTION_LOAD_GPR2 l.lwz r2,0x64(r0)

@@ -92,26 +129,32 @@
#define EXCEPTION_STORE_GPR6 l.sw 0x74(r0),r6
#define EXCEPTION_LOAD_GPR6 l.lwz r6,0x74(r0)

+#endif

/*
* EXCEPTION_HANDLE temporary stores
*/

+#ifdef CONFIG_OPENRISC_HAVE_SHADOW_GPRS
+#define EXCEPTION_T_STORE_GPR30 l.mtspr r0,r30,SPR_SHADOW_GPR(30)
+#define EXCEPTION_T_LOAD_GPR30(reg) l.mfspr reg,r0,SPR_SHADOW_GPR(30)
+
+#define EXCEPTION_T_STORE_GPR10 l.mtspr r0,r10,SPR_SHADOW_GPR(10)
+#define EXCEPTION_T_LOAD_GPR10(reg) l.mfspr reg,r0,SPR_SHADOW_GPR(10)
+
+#define EXCEPTION_T_STORE_SP l.mtspr r0,r1,SPR_SHADOW_GPR(1)
+#define EXCEPTION_T_LOAD_SP(reg) l.mfspr reg,r0,SPR_SHADOW_GPR(1)
+
+#else /* !CONFIG_OPENRISC_HAVE_SHADOW_GPRS */
#define EXCEPTION_T_STORE_GPR30 l.sw 0x78(r0),r30
#define EXCEPTION_T_LOAD_GPR30(reg) l.lwz reg,0x78(r0)

#define EXCEPTION_T_STORE_GPR10 l.sw 0x7c(r0),r10
#define EXCEPTION_T_LOAD_GPR10(reg) l.lwz reg,0x7c(r0)

-#define EXCEPTION_T_STORE_SP l.sw 0x80(r0),r1
+#define EXCEPTION_T_STORE_SP l.sw 0x80(r0),r1
#define EXCEPTION_T_LOAD_SP(reg) l.lwz reg,0x80(r0)
-
-/*
- * For UNHANLDED_EXCEPTION
- */
-
-#define EXCEPTION_T_STORE_GPR31 l.sw 0x84(r0),r31
-#define EXCEPTION_T_LOAD_GPR31(reg) l.lwz reg,0x84(r0)
+#endif

/* =========================================================[ macros ]=== */

@@ -226,7 +269,7 @@
*
*/
#define UNHANDLED_EXCEPTION(handler) \
- EXCEPTION_T_STORE_GPR31 ;\
+ EXCEPTION_T_STORE_GPR30 ;\
EXCEPTION_T_STORE_GPR10 ;\
EXCEPTION_T_STORE_SP ;\
/* temporary store r3, r9 into r1, r10 */ ;\
@@ -255,35 +298,35 @@
/* r1: KSP, r10: current, r31: __pa(KSP) */ ;\
/* r12: temp, syscall indicator, r13 temp */ ;\
l.addi r1,r1,-(INT_FRAME_SIZE) ;\
- /* r1 is KSP, r31 is __pa(KSP) */ ;\
- tophys (r31,r1) ;\
- l.sw PT_GPR12(r31),r12 ;\
+ /* r1 is KSP, r30 is __pa(KSP) */ ;\
+ tophys (r30,r1) ;\
+ l.sw PT_GPR12(r30),r12 ;\
l.mfspr r12,r0,SPR_EPCR_BASE ;\
- l.sw PT_PC(r31),r12 ;\
+ l.sw PT_PC(r30),r12 ;\
l.mfspr r12,r0,SPR_ESR_BASE ;\
- l.sw PT_SR(r31),r12 ;\
+ l.sw PT_SR(r30),r12 ;\
/* save r31 */ ;\
- EXCEPTION_T_LOAD_GPR31(r12) ;\
- l.sw PT_GPR31(r31),r12 ;\
+ EXCEPTION_T_LOAD_GPR30(r12) ;\
+ l.sw PT_GPR30(r30),r12 ;\
/* save r10 as was prior to exception */ ;\
EXCEPTION_T_LOAD_GPR10(r12) ;\
- l.sw PT_GPR10(r31),r12 ;\
+ l.sw PT_GPR10(r30),r12 ;\
/* save PT_SP as was prior to exception */ ;\
EXCEPTION_T_LOAD_SP(r12) ;\
- l.sw PT_SP(r31),r12 ;\
- l.sw PT_GPR13(r31),r13 ;\
+ l.sw PT_SP(r30),r12 ;\
+ l.sw PT_GPR13(r30),r13 ;\
/* --> */ ;\
/* save exception r4, set r4 = EA */ ;\
- l.sw PT_GPR4(r31),r4 ;\
+ l.sw PT_GPR4(r30),r4 ;\
l.mfspr r4,r0,SPR_EEAR_BASE ;\
/* r12 == 1 if we come from syscall */ ;\
CLEAR_GPR(r12) ;\
/* ----- play a MMU trick ----- */ ;\
- l.ori r31,r0,(EXCEPTION_SR) ;\
- l.mtspr r0,r31,SPR_ESR_BASE ;\
+ l.ori r30,r0,(EXCEPTION_SR) ;\
+ l.mtspr r0,r30,SPR_ESR_BASE ;\
/* r31: EA address of handler */ ;\
- LOAD_SYMBOL_2_GPR(r31,handler) ;\
- l.mtspr r0,r31,SPR_EPCR_BASE ;\
+ LOAD_SYMBOL_2_GPR(r30,handler) ;\
+ l.mtspr r0,r30,SPR_EPCR_BASE ;\
l.rfe

/* =====================================================[ exceptions] === */
--
2.13.6

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