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powerpc: merge 32-bit and 64-bit _switch implementation
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The _switch stack frame setup are substantially the same, so are the
comments. The difference in how the stack and current are switched,
and other hardware and software housekeeping is done is moved into
macros.

Generated code should be unchanged.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
[mpe: Tweak include orer to fix compile errors on some configs]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20230606132447.315714-6-npiggin@gmail.com
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Nicholas Piggin authored and Michael Ellerman committed Jun 15, 2023
1 parent 6958ad0 commit afc6386
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Showing 5 changed files with 273 additions and 282 deletions.
14 changes: 14 additions & 0 deletions arch/powerpc/include/asm/ppc_asm.h
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Expand Up @@ -406,6 +406,15 @@ GLUE(.,name):
/* offsets for stack frame layout */
#define LRSAVE 16

/*
* GCC stack frames follow a different pattern on 32 vs 64. This can be used
* to make asm frames be consistent with C.
*/
#define PPC_CREATE_STACK_FRAME(size) \
mflr r0; \
std r0,16(r1); \
stdu r1,-(size)(r1)

#else /* 32-bit */

#define LOAD_REG_IMMEDIATE(reg, expr) __LOAD_REG_IMMEDIATE_32 reg, expr
Expand All @@ -422,6 +431,11 @@ GLUE(.,name):
/* offsets for stack frame layout */
#define LRSAVE 4

#define PPC_CREATE_STACK_FRAME(size) \
stwu r1,-(size)(r1); \
mflr r0; \
stw r0,(size+4)(r1)

#endif

/* various errata or part fixups */
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2 changes: 1 addition & 1 deletion arch/powerpc/kernel/Makefile
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Expand Up @@ -68,7 +68,7 @@ CFLAGS_REMOVE_syscall.o = -fstack-protector -fstack-protector-strong
CFLAGS_syscall.o += -fno-stack-protector
#endif

obj-y := cputable.o syscalls.o \
obj-y := cputable.o syscalls.o switch.o \
irq.o align.o signal_$(BITS).o pmc.o vdso.o \
process.o systbl.o idle.o \
signal.o sysfs.o cacheinfo.o time.o \
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52 changes: 0 additions & 52 deletions arch/powerpc/kernel/entry_32.S
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Expand Up @@ -211,58 +211,6 @@ start_kernel_thread:
100: trap
EMIT_BUG_ENTRY 100b,__FILE__,__LINE__,0


/*
* This routine switches between two different tasks. The process
* state of one is saved on its kernel stack. Then the state
* of the other is restored from its kernel stack. The memory
* management hardware is updated to the second process's state.
* Finally, we can return to the second process.
* On entry, r3 points to the THREAD for the current task, r4
* points to the THREAD for the new task.
*
* This routine is always called with interrupts disabled.
*
* Note: there are two ways to get to the "going out" portion
* of this code; either by coming in via the entry (_switch)
* or via "fork" which must set up an environment equivalent
* to the "_switch" path. If you change this , you'll have to
* change the fork code also.
*
* The code which creates the new task context is in 'copy_thread'
* in arch/ppc/kernel/process.c
*/
_GLOBAL(_switch)
stwu r1,-SWITCH_FRAME_SIZE(r1)
mflr r0
stw r0,SWITCH_FRAME_SIZE+4(r1)
stw r1,KSP(r3) /* Set old stack pointer */
/* r3-r12 are caller saved -- Cort */
SAVE_NVGPRS(r1)
stw r0,_NIP(r1) /* Return to switch caller */
mfcr r0
stw r0,_CCR(r1)

/* The sync for SMP migration is taken care of, see entry_64.S */

tophys(r0,r4)
mtspr SPRN_SPRG_THREAD,r0 /* Update current THREAD phys addr */
lwz r1,KSP(r4) /* Load new stack pointer */

/* save the old current 'last' for return value */
mr r3,r2
addi r2,r4,-THREAD /* Update current */

lwz r0,_CCR(r1)
mtcrf 0xFF,r0
/* r3-r12 are destroyed -- Cort */
REST_NVGPRS(r1)

lwz r0,_NIP(r1) /* Return to _switch caller in new task */
mtlr r0
addi r1,r1,SWITCH_FRAME_SIZE
blr

.globl fast_exception_return
fast_exception_return:
#if !(defined(CONFIG_4xx) || defined(CONFIG_BOOKE))
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229 changes: 0 additions & 229 deletions arch/powerpc/kernel/entry_64.S
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Expand Up @@ -14,7 +14,6 @@
* code, and exception/interrupt return code for PowerPC.
*/

#include <linux/objtool.h>
#include <linux/errno.h>
#include <linux/err.h>
#include <asm/cache.h>
Expand Down Expand Up @@ -45,236 +44,8 @@
#include <asm/feature-fixups.h>
#include <asm/kup.h>

/*
* System calls.
*/
.section ".text"

#ifdef CONFIG_PPC_BOOK3S_64

#define FLUSH_COUNT_CACHE \
1: nop; \
patch_site 1b, patch__call_flush_branch_caches1; \
1: nop; \
patch_site 1b, patch__call_flush_branch_caches2; \
1: nop; \
patch_site 1b, patch__call_flush_branch_caches3

.macro nops number
.rept \number
nop
.endr
.endm

.balign 32
.global flush_branch_caches
flush_branch_caches:
/* Save LR into r9 */
mflr r9

// Flush the link stack
.rept 64
ANNOTATE_INTRA_FUNCTION_CALL
bl .+4
.endr
b 1f
nops 6

.balign 32
/* Restore LR */
1: mtlr r9

// If we're just flushing the link stack, return here
3: nop
patch_site 3b patch__flush_link_stack_return

li r9,0x7fff
mtctr r9

PPC_BCCTR_FLUSH

2: nop
patch_site 2b patch__flush_count_cache_return

nops 3

.rept 278
.balign 32
PPC_BCCTR_FLUSH
nops 7
.endr

blr

#ifdef CONFIG_PPC_64S_HASH_MMU
.balign 32
/*
* New stack pointer in r8, old stack pointer in r1, must not clobber r3
*/
pin_stack_slb:
BEGIN_FTR_SECTION
clrrdi r6,r8,28 /* get its ESID */
clrrdi r9,r1,28 /* get current sp ESID */
FTR_SECTION_ELSE
clrrdi r6,r8,40 /* get its 1T ESID */
clrrdi r9,r1,40 /* get current sp 1T ESID */
ALT_MMU_FTR_SECTION_END_IFCLR(MMU_FTR_1T_SEGMENT)
clrldi. r0,r6,2 /* is new ESID c00000000? */
cmpd cr1,r6,r9 /* or is new ESID the same as current ESID? */
cror eq,4*cr1+eq,eq
beq 2f /* if yes, don't slbie it */

/* Bolt in the new stack SLB entry */
ld r7,KSP_VSID(r4) /* Get new stack's VSID */
oris r0,r6,(SLB_ESID_V)@h
ori r0,r0,(SLB_NUM_BOLTED-1)@l
BEGIN_FTR_SECTION
li r9,MMU_SEGSIZE_1T /* insert B field */
oris r6,r6,(MMU_SEGSIZE_1T << SLBIE_SSIZE_SHIFT)@h
rldimi r7,r9,SLB_VSID_SSIZE_SHIFT,0
END_MMU_FTR_SECTION_IFSET(MMU_FTR_1T_SEGMENT)

/* Update the last bolted SLB. No write barriers are needed
* here, provided we only update the current CPU's SLB shadow
* buffer.
*/
ld r9,PACA_SLBSHADOWPTR(r13)
li r12,0
std r12,SLBSHADOW_STACKESID(r9) /* Clear ESID */
li r12,SLBSHADOW_STACKVSID
STDX_BE r7,r12,r9 /* Save VSID */
li r12,SLBSHADOW_STACKESID
STDX_BE r0,r12,r9 /* Save ESID */

/* No need to check for MMU_FTR_NO_SLBIE_B here, since when
* we have 1TB segments, the only CPUs known to have the errata
* only support less than 1TB of system memory and we'll never
* actually hit this code path.
*/

isync
slbie r6
BEGIN_FTR_SECTION
slbie r6 /* Workaround POWER5 < DD2.1 issue */
END_FTR_SECTION_IFCLR(CPU_FTR_ARCH_207S)
slbmte r7,r0
isync
2: blr
.size pin_stack_slb,.-pin_stack_slb
#endif /* CONFIG_PPC_64S_HASH_MMU */

#else
#define FLUSH_COUNT_CACHE
#endif /* CONFIG_PPC_BOOK3S_64 */

/*
* This routine switches between two different tasks. The process
* state of one is saved on its kernel stack. Then the state
* of the other is restored from its kernel stack. The memory
* management hardware is updated to the second process's state.
* Finally, we can return to the second process, via interrupt_return.
* On entry, r3 points to the THREAD for the current task, r4
* points to the THREAD for the new task.
*
* Note: there are two ways to get to the "going out" portion
* of this code; either by coming in via the entry (_switch)
* or via "fork" which must set up an environment equivalent
* to the "_switch" path. If you change this you'll have to change
* the fork code also.
*
* The code which creates the new task context is in 'copy_thread'
* in arch/powerpc/kernel/process.c
*/
.align 7
_GLOBAL(_switch)
mflr r0
std r0,16(r1)
stdu r1,-SWITCH_FRAME_SIZE(r1)
std r1,KSP(r3) /* Set old stack pointer */
/* r3-r13 are caller saved -- Cort */
SAVE_NVGPRS(r1)
std r0,_NIP(r1) /* Return to switch caller */
mfcr r0
stw r0,_CCR(r1)
ld r8,KSP(r4) /* Load new stack pointer */

kuap_check_amr r9, r10

FLUSH_COUNT_CACHE /* Clobbers r9, ctr */

/*
* On SMP kernels, care must be taken because a task may be
* scheduled off CPUx and on to CPUy. Memory ordering must be
* considered.
*
* Cacheable stores on CPUx will be visible when the task is
* scheduled on CPUy by virtue of the core scheduler barriers
* (see "Notes on Program-Order guarantees on SMP systems." in
* kernel/sched/core.c).
*
* Uncacheable stores in the case of involuntary preemption must
* be taken care of. The smp_mb__after_spinlock() in __schedule()
* is implemented as hwsync on powerpc, which orders MMIO too. So
* long as there is an hwsync in the context switch path, it will
* be executed on the source CPU after the task has performed
* all MMIO ops on that CPU, and on the destination CPU before the
* task performs any MMIO ops there.
*/

/*
* The kernel context switch path must contain a spin_lock,
* which contains larx/stcx, which will clear any reservation
* of the task being switched.
*/
#ifdef CONFIG_PPC_BOOK3S
/* Cancel all explict user streams as they will have no use after context
* switch and will stop the HW from creating streams itself
*/
DCBT_BOOK3S_STOP_ALL_STREAM_IDS(r6)
#endif

addi r3,r3,-THREAD /* old thread -> task_struct for return value */
addi r6,r4,-THREAD /* new thread -> task_struct */
std r6,PACACURRENT(r13) /* Set new task_struct to 'current' */
#if defined(CONFIG_STACKPROTECTOR)
ld r6, TASK_CANARY(r6)
std r6, PACA_CANARY(r13)
#endif
/* Set the new PACAKSAVE */
clrrdi r7, r8, THREAD_SHIFT /* base of new stack */
/* Note: this uses SWITCH_FRAME_SIZE rather than INT_FRAME_SIZE
because we don't need to leave the 288-byte ABI gap at the
top of the kernel stack. */
addi r7,r7,THREAD_SIZE-SWITCH_FRAME_SIZE
std r7,PACAKSAVE(r13)

#ifdef CONFIG_PPC_64S_HASH_MMU
BEGIN_MMU_FTR_SECTION
bl pin_stack_slb
END_MMU_FTR_SECTION_IFCLR(MMU_FTR_TYPE_RADIX)
#endif

/*
* PMU interrupts in radix may come in here. They will use r1, not
* PACAKSAVE, so this stack switch will not cause a problem. They
* will store to the process stack, which may then be migrated to
* another CPU. However the rq lock release on this CPU paired with
* the rq lock acquire on the new CPU before the stack becomes
* active on the new CPU, will order those stores.
*/
mr r1,r8 /* start using new stack pointer */

lwz r0,_CCR(r1)
mtcrf 0xFF,r0

/* r3-r13 are destroyed -- Cort */
REST_NVGPRS(r1)

ld r0,_NIP(r1) /* Return to _switch caller in new task */
mtlr r0
addi r1,r1,SWITCH_FRAME_SIZE
blr

_GLOBAL(enter_prom)
mflr r0
std r0,16(r1)
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