x86: add %gs accessors for x86_32

Impact: cleanup

On x86_32, %gs is handled lazily.  It's not saved and restored on
kernel entry/exit but only when necessary which usually is during task
switch but there are few other places.  Currently, it's done by
calling savesegment() and loadsegment() explicitly.  Define
get_user_gs(), set_user_gs() and task_user_gs() and use them instead.

While at it, clean up register access macros in signal.c.

This cleans up code a bit and will help future changes.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

9 files changed, 41 insertions, 45 deletions

diff --git a/arch/x86/include/asm/a.out-core.h b/arch/x86/include/asm/a.out-core.h
index 3c601f8224be..bb70e397aa84 100644
--- a/arch/x86/include/asm/a.out-core.h
+++ b/arch/x86/include/asm/a.out-core.h
@@ -55,7 +55,7 @@ static inline void aout_dump_thread(struct pt_regs *regs, struct user *dump)
         dump->regs.ds = (u16)regs->ds;
         dump->regs.es = (u16)regs->es;
         dump->regs.fs = (u16)regs->fs;
-        savesegment(gs, dump->regs.gs);
+        dump->regs.gs = get_user_gs(regs);
         dump->regs.orig_ax = regs->orig_ax;
         dump->regs.ip = regs->ip;
         dump->regs.cs = (u16)regs->cs;
diff --git a/arch/x86/include/asm/elf.h b/arch/x86/include/asm/elf.h
index f51a3ddde01a..39b0aac1675c 100644
--- a/arch/x86/include/asm/elf.h
+++ b/arch/x86/include/asm/elf.h
@@ -124,7 +124,7 @@ do {						\
         pr_reg[7] = regs->ds & 0xffff;          \
         pr_reg[8] = regs->es & 0xffff;          \
         pr_reg[9] = regs->fs & 0xffff;          \
-        savesegment(gs, pr_reg[10]);            \
+        pr_reg[10] = get_user_gs(regs);         \
         pr_reg[11] = regs->orig_ax;             \
         pr_reg[12] = regs->ip;                  \
         pr_reg[13] = regs->cs & 0xffff;         \
diff --git a/arch/x86/include/asm/mmu_context.h b/arch/x86/include/asm/mmu_context.h
index 52948df9cd1d..4955165682c5 100644
--- a/arch/x86/include/asm/mmu_context.h
+++ b/arch/x86/include/asm/mmu_context.h
@@ -79,7 +79,7 @@ do {						\
 #ifdef CONFIG_X86_32
 #define deactivate_mm(tsk, mm)                  \
 do {                                            \
-        loadsegment(gs, 0);                     \
+        set_user_gs(task_pt_regs(tsk), 0);      \
 } while (0)
 #else
 #define deactivate_mm(tsk, mm)                  \
diff --git a/arch/x86/include/asm/system.h b/arch/x86/include/asm/system.h
index 2fcc70bc85f3..70c74b8db875 100644
--- a/arch/x86/include/asm/system.h
+++ b/arch/x86/include/asm/system.h
@@ -182,6 +182,15 @@ extern void native_load_gs_index(unsigned);
 #define savesegment(seg, value)                         \
         asm("mov %%" #seg ",%0":"=r" (value) : : "memory")
 
+/*
+ * x86_32 user gs accessors.
+ */
+#ifdef CONFIG_X86_32
+#define get_user_gs(regs)       (u16)({unsigned long v; savesegment(gs, v); v;})
+#define set_user_gs(regs, v)    loadsegment(gs, (unsigned long)(v))
+#define task_user_gs(tsk)       ((tsk)->thread.gs)
+#endif
+
 static inline unsigned long get_limit(unsigned long segment)
 {
         unsigned long __limit;
diff --git a/arch/x86/kernel/process_32.c b/arch/x86/kernel/process_32.c
index 1a1ae8edc40c..d58a340e1be3 100644
--- a/arch/x86/kernel/process_32.c
+++ b/arch/x86/kernel/process_32.c
@@ -131,7 +131,7 @@ void __show_regs(struct pt_regs *regs, int all)
         if (user_mode_vm(regs)) {
                 sp = regs->sp;
                 ss = regs->ss & 0xffff;
-                savesegment(gs, gs);
+                gs = get_user_gs(regs);
         } else {
                 sp = (unsigned long) (&regs->sp);
                 savesegment(ss, ss);
@@ -304,7 +304,7 @@ int copy_thread(int nr, unsigned long clone_flags, unsigned long sp,
 
         p->thread.ip = (unsigned long) ret_from_fork;
 
-        savesegment(gs, p->thread.gs);
+        task_user_gs(p) = get_user_gs(regs);
 
         tsk = current;
         if (unlikely(test_tsk_thread_flag(tsk, TIF_IO_BITMAP))) {
@@ -342,7 +342,7 @@ int copy_thread(int nr, unsigned long clone_flags, unsigned long sp,
 void
 start_thread(struct pt_regs *regs, unsigned long new_ip, unsigned long new_sp)
 {
-        __asm__("movl %0, %%gs" : : "r"(0));
+        set_user_gs(regs, 0);
         regs->fs                = 0;
         set_fs(USER_DS);
         regs->ds                = __USER_DS;
diff --git a/arch/x86/kernel/ptrace.c b/arch/x86/kernel/ptrace.c
index 0a5df5f82fb9..508b6b57d0c3 100644
--- a/arch/x86/kernel/ptrace.c
+++ b/arch/x86/kernel/ptrace.c
@@ -90,9 +90,10 @@ static u16 get_segment_reg(struct task_struct *task, unsigned long offset)
         if (offset != offsetof(struct user_regs_struct, gs))
                 retval = *pt_regs_access(task_pt_regs(task), offset);
         else {
-                retval = task->thread.gs;
                 if (task == current)
-                        savesegment(gs, retval);
+                        retval = get_user_gs(task_pt_regs(task));
+                else
+                        retval = task_user_gs(task);
         }
         return retval;
 }
@@ -126,13 +127,10 @@ static int set_segment_reg(struct task_struct *task,
                 break;
 
         case offsetof(struct user_regs_struct, gs):
-                task->thread.gs = value;
                 if (task == current)
-                        /*
-                         * The user-mode %gs is not affected by
-                         * kernel entry, so we must update the CPU.
-                         */
-                        loadsegment(gs, value);
+                        set_user_gs(task_pt_regs(task), value);
+                else
+                        task_user_gs(task) = value;
         }
 
         return 0;
diff --git a/arch/x86/kernel/signal.c b/arch/x86/kernel/signal.c
index 7fc78b019815..8562387c75a7 100644
--- a/arch/x86/kernel/signal.c
+++ b/arch/x86/kernel/signal.c
@@ -50,27 +50,23 @@
 # define FIX_EFLAGS     __FIX_EFLAGS
 #endif
 
-#define COPY(x)                 {               \
-        get_user_ex(regs->x, &sc->x);           \
-}
+#define COPY(x)                 do {                    \
+        get_user_ex(regs->x, &sc->x);                   \
+} while (0)
 
-#define COPY_SEG(seg)           {                       \
-                unsigned short tmp;                     \
-                get_user_ex(tmp, &sc->seg);             \
-                regs->seg = tmp;                        \
-}
+#define GET_SEG(seg)            ({                      \
+        unsigned short tmp;                             \
+        get_user_ex(tmp, &sc->seg);                     \
+        tmp;                                            \
+})
 
-#define COPY_SEG_CPL3(seg)      {                       \
-                unsigned short tmp;                     \
-                get_user_ex(tmp, &sc->seg);             \
-                regs->seg = tmp | 3;                    \
-}
+#define COPY_SEG(seg)           do {                    \
+        regs->seg = GET_SEG(seg);                       \
+} while (0)
 
-#define GET_SEG(seg)            {                       \
-                unsigned short tmp;                     \
-                get_user_ex(tmp, &sc->seg);             \
-                loadsegment(seg, tmp);                  \
-}
+#define COPY_SEG_CPL3(seg)      do {                    \
+        regs->seg = GET_SEG(seg) | 3;                   \
+} while (0)
 
 static int
 restore_sigcontext(struct pt_regs *regs, struct sigcontext __user *sc,
@@ -86,7 +82,7 @@ restore_sigcontext(struct pt_regs *regs, struct sigcontext __user *sc,
         get_user_try {
 
 #ifdef CONFIG_X86_32
-                GET_SEG(gs);
+                set_user_gs(regs, GET_SEG(gs));
                 COPY_SEG(fs);
                 COPY_SEG(es);
                 COPY_SEG(ds);
@@ -138,12 +134,7 @@ setup_sigcontext(struct sigcontext __user *sc, void __user *fpstate,
         put_user_try {
 
 #ifdef CONFIG_X86_32
-                {
-                        unsigned int tmp;
-
-                        savesegment(gs, tmp);
-                        put_user_ex(tmp, (unsigned int __user *)&sc->gs);
-                }
+                put_user_ex(get_user_gs(regs), (unsigned int __user *)&sc->gs);
                 put_user_ex(regs->fs, (unsigned int __user *)&sc->fs);
                 put_user_ex(regs->es, (unsigned int __user *)&sc->es);
                 put_user_ex(regs->ds, (unsigned int __user *)&sc->ds);
diff --git a/arch/x86/kernel/vm86_32.c b/arch/x86/kernel/vm86_32.c
index 4eeb5cf9720d..55ea30d2a3d6 100644
--- a/arch/x86/kernel/vm86_32.c
+++ b/arch/x86/kernel/vm86_32.c
@@ -158,7 +158,7 @@ struct pt_regs *save_v86_state(struct kernel_vm86_regs *regs)
         ret = KVM86->regs32;
 
         ret->fs = current->thread.saved_fs;
-        loadsegment(gs, current->thread.saved_gs);
+        set_user_gs(ret, current->thread.saved_gs);
 
         return ret;
 }
@@ -323,7 +323,7 @@ static void do_sys_vm86(struct kernel_vm86_struct *info, struct task_struct *tsk
         info->regs32->ax = 0;
         tsk->thread.saved_sp0 = tsk->thread.sp0;
         tsk->thread.saved_fs = info->regs32->fs;
-        savesegment(gs, tsk->thread.saved_gs);
+        tsk->thread.saved_gs = get_user_gs(info->regs32);
 
         tss = &per_cpu(init_tss, get_cpu());
         tsk->thread.sp0 = (unsigned long) &info->VM86_TSS_ESP0;
diff --git a/arch/x86/math-emu/get_address.c b/arch/x86/math-emu/get_address.c
index 420b3b6e3915..6ef5e99380f9 100644
--- a/arch/x86/math-emu/get_address.c
+++ b/arch/x86/math-emu/get_address.c
@@ -150,11 +150,9 @@ static long pm_address(u_char FPU_modrm, u_char segment,
 #endif /* PARANOID */
 
         switch (segment) {
-                /* gs isn't used by the kernel, so it still has its
-                   user-space value. */
         case PREFIX_GS_ - 1:
-                /* N.B. - movl %seg, mem is a 2 byte write regardless of prefix */
-                savesegment(gs, addr->selector);
+                /* user gs handling can be lazy, use special accessors */
+                addr->selector = get_user_gs(FPU_info->regs);
                 break;
         default:
                 addr->selector = PM_REG_(segment);