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.de
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>

4 files changed, 9 insertions, 15 deletions

diff --git a/arch/m68k/kernel/asm-offsets.c b/arch/m68k/kernel/asm-offsets.c
index ccea355052ef..906d73230537 100644
--- a/arch/m68k/kernel/asm-offsets.c
+++ b/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));
diff --git a/arch/m68k/kernel/entry.S b/arch/m68k/kernel/entry.S
index 8fa9822b5922..9434fca68de5 100644
--- a/arch/m68k/kernel/entry.S
+++ b/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
 
diff --git a/arch/m68k/kernel/process.c b/arch/m68k/kernel/process.c
index db49f9091711..1ab692b952cd 100644
--- a/arch/m68k/kernel/process.c
+++ b/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 */
diff --git a/arch/m68k/kernel/traps.c b/arch/m68k/kernel/traps.c
index 5b19fcdcd69e..9718ce94cc84 100644
--- a/arch/m68k/kernel/traps.c
+++ b/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);