m68k: Remove set_fs()

Add a m68k-only set_fc helper to set the SFC and DFC registers for the
few places that need to override it for special MM operations, but
disconnect that from the deprecated kernel-wide set_fs() API.

Note that the SFC/DFC registers are context switched, so there is no need
to disable preemption.

Partially based on an earlier patch from
Linus Torvalds <torvalds@linux-foundation.org>.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Michael Schmitz <schmitzmic@gmail.com>
Tested-by: Michael Schmitz <schmitzmic@gmail.com>
Link: https://lore.kernel.org/r/20210916070405.52750-7-hch@lst.deSigned-off-by: Geert Uytterhoeven <geert@linux-m68k.org>

arch/m68k/68000/entry.S

@@ -15,7 +15,6 @@
 #include <asm/unistd.h>
 #include <asm/errno.h>
 #include <asm/setup.h>
-#include <asm/segment.h>
 #include <asm/traps.h>
 #include <asm/asm-offsets.h>
 #include <asm/entry.h>

arch/m68k/Kconfig

@@ -29,7 +29,6 @@ config M68K
 	select NO_DMA if !MMU && !COLDFIRE
 	select OLD_SIGACTION
 	select OLD_SIGSUSPEND3
-	select SET_FS
 	select UACCESS_MEMCPY if !MMU
 	select VIRT_TO_BUS
 	select ZONE_DMA

arch/m68k/coldfire/entry.S

@@ -31,7 +31,6 @@
 #include <asm/thread_info.h>
 #include <asm/errno.h>
 #include <asm/setup.h>
-#include <asm/segment.h>
 #include <asm/asm-offsets.h>
 #include <asm/entry.h>
 

arch/m68k/include/asm/processor.h

@@ -9,7 +9,6 @@
 #define __ASM_M68K_PROCESSOR_H
 
 #include <linux/thread_info.h>
-#include <asm/segment.h>
 #include <asm/fpu.h>
 #include <asm/ptrace.h>
 
@@ -75,11 +74,37 @@ static inline void wrusp(unsigned long usp)
 #define TASK_UNMAPPED_BASE	0
 #endif
 
+/* Address spaces (or Function Codes in Motorola lingo) */
+#define USER_DATA     1
+#define USER_PROGRAM  2
+#define SUPER_DATA    5
+#define SUPER_PROGRAM 6
+#define CPU_SPACE     7
+
+#ifdef CONFIG_CPU_HAS_ADDRESS_SPACES
+/*
+ * Set the SFC/DFC registers for special MM operations.  For most normal
+ * operation these remain set to USER_DATA for the uaccess routines.
+ */
+static inline void set_fc(unsigned long val)
+{
+	WARN_ON_ONCE(in_interrupt());
+
+	__asm__ __volatile__ ("movec %0,%/sfc\n\t"
+			      "movec %0,%/dfc\n\t"
+			      : /* no outputs */ : "r" (val) : "memory");
+}
+#else
+static inline void set_fc(unsigned long val)
+{
+}
+#endif /* CONFIG_CPU_HAS_ADDRESS_SPACES */
+
 struct thread_struct {
 	unsigned long  ksp;		/* kernel stack pointer */
 	unsigned long  usp;		/* user stack pointer */
 	unsigned short sr;		/* saved status register */
-	unsigned short fs;		/* saved fs (sfc, dfc) */
+	unsigned short fc;		/* saved fc (sfc, dfc) */
 	unsigned long  crp[2];		/* cpu root pointer */
 	unsigned long  esp0;		/* points to SR of stack frame */
 	unsigned long  faddr;		/* info about last fault */
@@ -92,7 +117,7 @@ struct thread_struct {
 #define INIT_THREAD  {							\
 	.ksp	= sizeof(init_stack) + (unsigned long) init_stack,	\
 	.sr	= PS_S,							\
-	.fs	= __KERNEL_DS,						\
+	.fc	= USER_DATA,						\
 }
 
 /*

arch/m68k/include/asm/segment.h

-/* SPDX-License-Identifier: GPL-2.0 */
-#ifndef _M68K_SEGMENT_H
-#define _M68K_SEGMENT_H
-
-/* define constants */
-/* Address spaces (FC0-FC2) */
-#define USER_DATA     (1)
-#ifndef __USER_DS
-#define __USER_DS     (USER_DATA)
-#endif
-#define USER_PROGRAM  (2)
-#define SUPER_DATA    (5)
-#ifndef __KERNEL_DS
-#define __KERNEL_DS   (SUPER_DATA)
-#endif
-#define SUPER_PROGRAM (6)
-#define CPU_SPACE     (7)
-
-#ifndef __ASSEMBLY__
-
-typedef struct {
-	unsigned long seg;
-} mm_segment_t;
-
-#define MAKE_MM_SEG(s)	((mm_segment_t) { (s) })
-
-#ifdef CONFIG_CPU_HAS_ADDRESS_SPACES
-/*
- * Get/set the SFC/DFC registers for MOVES instructions
- */
-#define USER_DS		MAKE_MM_SEG(__USER_DS)
-#define KERNEL_DS	MAKE_MM_SEG(__KERNEL_DS)
-
-static inline mm_segment_t get_fs(void)
-{
-	mm_segment_t _v;
-	__asm__ ("movec %/dfc,%0":"=r" (_v.seg):);
-	return _v;
-}
-
-static inline void set_fs(mm_segment_t val)
-{
-	__asm__ __volatile__ ("movec %0,%/sfc\n\t"
-			      "movec %0,%/dfc\n\t"
-			      : /* no outputs */ : "r" (val.seg) : "memory");
-}
-
-#else
-#define USER_DS		MAKE_MM_SEG(TASK_SIZE)
-#define KERNEL_DS	MAKE_MM_SEG(0xFFFFFFFF)
-#define get_fs()	(current_thread_info()->addr_limit)
-#define set_fs(x)	(current_thread_info()->addr_limit = (x))
-#endif
-
-#define uaccess_kernel()	(get_fs().seg == KERNEL_DS.seg)
-
-#endif /* __ASSEMBLY__ */
-
-#endif /* _M68K_SEGMENT_H */

arch/m68k/include/asm/thread_info.h

@@ -4,7 +4,6 @@
 
 #include <asm/types.h>
 #include <asm/page.h>
-#include <asm/segment.h>
 
 /*
  * On machines with 4k pages we default to an 8k thread size, though we
@@ -27,7 +26,6 @@
 struct thread_info {
 	struct task_struct	*task;		/* main task structure */
 	unsigned long		flags;
-	mm_segment_t		addr_limit;	/* thread address space */
 	int			preempt_count;	/* 0 => preemptable, <0 => BUG */
 	__u32			cpu;		/* should always be 0 on m68k */
 	unsigned long		tp_value;	/* thread pointer */
@@ -37,7 +35,6 @@ struct thread_info {
 #define INIT_THREAD_INFO(tsk)			\
 {						\
 	.task		= &tsk,			\
-	.addr_limit	= KERNEL_DS,		\
 	.preempt_count	= INIT_PREEMPT_COUNT,	\
 }
 

arch/m68k/include/asm/tlbflush.h

@@ -13,13 +13,12 @@ static inline void flush_tlb_kernel_page(void *addr)
 	if (CPU_IS_COLDFIRE) {
 		mmu_write(MMUOR, MMUOR_CNL);
 	} else if (CPU_IS_040_OR_060) {
-		mm_segment_t old_fs = get_fs();
-		set_fs(KERNEL_DS);
+		set_fc(SUPER_DATA);
 		__asm__ __volatile__(".chip 68040\n\t"
 				     "pflush (%0)\n\t"
 				     ".chip 68k"
 				     : : "a" (addr));
-		set_fs(old_fs);
+		set_fc(USER_DATA);
 	} else if (CPU_IS_020_OR_030)
 		__asm__ __volatile__("pflush #4,#4,(%0)" : : "a" (addr));
 }
@@ -84,12 +83,8 @@ static inline void flush_tlb_mm(struct mm_struct *mm)
 
 static inline void flush_tlb_page(struct vm_area_struct *vma, unsigned long addr)
 {
-	if (vma->vm_mm == current->active_mm) {
-		mm_segment_t old_fs = force_uaccess_begin();
-
+	if (vma->vm_mm == current->active_mm)
 		__flush_tlb_one(addr);
-		force_uaccess_end(old_fs);
-	}
 }
 
 static inline void flush_tlb_range(struct vm_area_struct *vma,

arch/m68k/include/asm/uaccess.h

@@ -9,7 +9,6 @@
  */
 #include <linux/compiler.h>
 #include <linux/types.h>
-#include <asm/segment.h>
 #include <asm/extable.h>
 
 /* We let the MMU do all checking */
@@ -451,9 +450,6 @@ do {									\
 		goto err_label;						\
 } while (0)
 
-#define user_addr_max() \
-	(uaccess_kernel() ? ~0UL : TASK_SIZE)
-
 extern long strncpy_from_user(char *dst, const char __user *src, long count);
 extern __must_check long strnlen_user(const char __user *str, long n);
 

arch/m68k/kernel/asm-offsets.c

@@ -31,7 +31,7 @@ int main(void)
 	DEFINE(THREAD_KSP, offsetof(struct thread_struct, ksp));
 	DEFINE(THREAD_USP, offsetof(struct thread_struct, usp));
 	DEFINE(THREAD_SR, offsetof(struct thread_struct, sr));
-	DEFINE(THREAD_FS, offsetof(struct thread_struct, fs));
+	DEFINE(THREAD_FC, offsetof(struct thread_struct, fc));
 	DEFINE(THREAD_CRP, offsetof(struct thread_struct, crp));
 	DEFINE(THREAD_ESP0, offsetof(struct thread_struct, esp0));
 	DEFINE(THREAD_FPREG, offsetof(struct thread_struct, fp));

arch/m68k/kernel/entry.S

@@ -36,7 +36,6 @@
 #include <linux/linkage.h>
 #include <asm/errno.h>
 #include <asm/setup.h>
-#include <asm/segment.h>
 #include <asm/traps.h>
 #include <asm/unistd.h>
 #include <asm/asm-offsets.h>
@@ -337,7 +336,7 @@ resume:
 
 	/* save fs (sfc,%dfc) (may be pointing to kernel memory) */
 	movec	%sfc,%d0
-	movew	%d0,%a0@(TASK_THREAD+THREAD_FS)
+	movew	%d0,%a0@(TASK_THREAD+THREAD_FC)
 
 	/* save usp */
 	/* it is better to use a movel here instead of a movew 8*) */
@@ -423,7 +422,7 @@ resume:
 	movel	%a0,%usp
 
 	/* restore fs (sfc,%dfc) */
-	movew	%a1@(TASK_THREAD+THREAD_FS),%a0
+	movew	%a1@(TASK_THREAD+THREAD_FC),%a0
 	movec	%a0,%sfc
 	movec	%a0,%dfc
 

arch/m68k/kernel/process.c

@@ -92,7 +92,7 @@ void show_regs(struct pt_regs * regs)
 
 void flush_thread(void)
 {
-	current->thread.fs = __USER_DS;
+	current->thread.fc = USER_DATA;
 #ifdef CONFIG_FPU
 	if (!FPU_IS_EMU) {
 		unsigned long zero = 0;
@@ -155,7 +155,7 @@ int copy_thread(unsigned long clone_flags, unsigned long usp, unsigned long arg,
 	 * Must save the current SFC/DFC value, NOT the value when
 	 * the parent was last descheduled - RGH  10-08-96
 	 */
-	p->thread.fs = get_fs().seg;
+	p->thread.fc = USER_DATA;
 
 	if (unlikely(p->flags & (PF_KTHREAD | PF_IO_WORKER))) {
 		/* kernel thread */

arch/m68k/kernel/traps.c

@@ -181,9 +181,8 @@ static inline void access_error060 (struct frame *fp)
 static inline unsigned long probe040(int iswrite, unsigned long addr, int wbs)
 {
 	unsigned long mmusr;
-	mm_segment_t old_fs = get_fs();
 
-	set_fs(MAKE_MM_SEG(wbs));
+	set_fc(wbs);
 
 	if (iswrite)
 		asm volatile (".chip 68040; ptestw (%0); .chip 68k" : : "a" (addr));
@@ -192,7 +191,7 @@ static inline unsigned long probe040(int iswrite, unsigned long addr, int wbs)
 
 	asm volatile (".chip 68040; movec %%mmusr,%0; .chip 68k" : "=r" (mmusr));
 
-	set_fs(old_fs);
+	set_fc(USER_DATA);
 
 	return mmusr;
 }
@@ -201,10 +200,8 @@ static inline int do_040writeback1(unsigned short wbs, unsigned long wba,
 				   unsigned long wbd)
 {
 	int res = 0;
-	mm_segment_t old_fs = get_fs();
 
-	/* set_fs can not be moved, otherwise put_user() may oops */
-	set_fs(MAKE_MM_SEG(wbs));
+	set_fc(wbs);
 
 	switch (wbs & WBSIZ_040) {
 	case BA_SIZE_BYTE:
@@ -218,9 +215,7 @@ static inline int do_040writeback1(unsigned short wbs, unsigned long wba,
 		break;
 	}
 
-	/* set_fs can not be moved, otherwise put_user() may oops */
-	set_fs(old_fs);
-
+	set_fc(USER_DATA);
 
 	pr_debug("do_040writeback1, res=%d\n", res);
 

arch/m68k/mac/misc.c

@@ -18,7 +18,6 @@
 
 #include <linux/uaccess.h>
 #include <asm/io.h>
-#include <asm/segment.h>
 #include <asm/setup.h>
 #include <asm/macintosh.h>
 #include <asm/mac_via.h>

arch/m68k/mm/cache.c

@@ -90,11 +90,9 @@ void flush_icache_user_range(unsigned long address, unsigned long endaddr)
 
 void flush_icache_range(unsigned long address, unsigned long endaddr)
 {
-	mm_segment_t old_fs = get_fs();
-
-	set_fs(KERNEL_DS);
+	set_fc(SUPER_DATA);
 	flush_icache_user_range(address, endaddr);
-	set_fs(old_fs);
+	set_fc(USER_DATA);
 }
 EXPORT_SYMBOL(flush_icache_range);
 

arch/m68k/mm/init.c

@@ -72,12 +72,6 @@ void __init paging_init(void)
 	if (!empty_zero_page)
 		panic("%s: Failed to allocate %lu bytes align=0x%lx\n",
 		      __func__, PAGE_SIZE, PAGE_SIZE);
-
-	/*
-	 * Set up SFC/DFC registers (user data space).
-	 */
-	set_fs (USER_DS);
-
 	max_zone_pfn[ZONE_DMA] = end_mem >> PAGE_SHIFT;
 	free_area_init(max_zone_pfn);
 }

arch/m68k/mm/kmap.c

@@ -17,7 +17,6 @@
 #include <linux/vmalloc.h>
 
 #include <asm/setup.h>
-#include <asm/segment.h>
 #include <asm/page.h>
 #include <asm/io.h>
 #include <asm/tlbflush.h>

arch/m68k/mm/memory.c

@@ -15,7 +15,6 @@
 #include <linux/gfp.h>
 
 #include <asm/setup.h>
-#include <asm/segment.h>
 #include <asm/page.h>
 #include <asm/traps.h>
 #include <asm/machdep.h>

arch/m68k/mm/motorola.c

@@ -467,7 +467,7 @@ void __init paging_init(void)
 	/*
 	 * Set up SFC/DFC registers
 	 */
-	set_fs(KERNEL_DS);
+	set_fc(USER_DATA);
 
 #ifdef DEBUG
 	printk ("before free_area_init\n");

arch/m68k/sun3/config.c

@@ -31,7 +31,6 @@
 #include <asm/intersil.h>
 #include <asm/irq.h>
 #include <asm/sections.h>
-#include <asm/segment.h>
 #include <asm/sun3ints.h>
 
 char sun3_reserved_pmeg[SUN3_PMEGS_NUM];
@@ -89,7 +88,7 @@ void __init sun3_init(void)
 	sun3_reserved_pmeg[249] = 1;
 	sun3_reserved_pmeg[252] = 1;
 	sun3_reserved_pmeg[253] = 1;
-	set_fs(KERNEL_DS);
+	set_fc(USER_DATA);
 }
 
 /* Without this, Bad Things happen when something calls arch_reset. */

arch/m68k/sun3/mmu_emu.c

@@ -23,7 +23,6 @@
 #include <linux/uaccess.h>
 #include <asm/page.h>
 #include <asm/sun3mmu.h>
-#include <asm/segment.h>
 #include <asm/oplib.h>
 #include <asm/mmu_context.h>
 #include <asm/dvma.h>
@@ -191,14 +190,13 @@ void __init mmu_emu_init(unsigned long bootmem_end)
 	for(seg = 0; seg < PAGE_OFFSET; seg += SUN3_PMEG_SIZE)
 		sun3_put_segmap(seg, SUN3_INVALID_PMEG);
 
-	set_fs(MAKE_MM_SEG(3));
+	set_fc(3);
 	for(seg = 0; seg < 0x10000000; seg += SUN3_PMEG_SIZE) {
 		i = sun3_get_segmap(seg);
 		for(j = 1; j < CONTEXTS_NUM; j++)
 			(*(romvec->pv_setctxt))(j, (void *)seg, i);
 	}
-	set_fs(KERNEL_DS);
-
+	set_fc(USER_DATA);
 }
 
 /* erase the mappings for a dead context.  Uses the pg_dir for hints

arch/m68k/sun3/sun3ints.c

@@ -11,7 +11,6 @@
 #include <linux/sched.h>
 #include <linux/kernel_stat.h>
 #include <linux/interrupt.h>
-#include <asm/segment.h>
 #include <asm/intersil.h>
 #include <asm/oplib.h>
 #include <asm/sun3ints.h>

arch/m68k/sun3x/prom.c

@@ -14,7 +14,6 @@
 #include <asm/traps.h>
 #include <asm/sun3xprom.h>
 #include <asm/idprom.h>
-#include <asm/segment.h>
 #include <asm/sun3ints.h>
 #include <asm/openprom.h>
 #include <asm/machines.h>