[PATCH 09/11] x86: add %gs accessors for x86_32

Tejun Heo
2009-02-09T13:43:55Z

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>
---
arch/x86/include/asm/a.out-core.h | 2 +-
arch/x86/include/asm/elf.h | 2 +-
arch/x86/include/asm/mmu_context.h | 2 +-
arch/x86/include/asm/system.h | 9 ++++++++
arch/x86/kernel/process_32.c | 6 ++--
arch/x86/kernel/ptrace.c | 14 +++++-------
arch/x86/kernel/signal.c | 41 ++++++++++++++----------------------
arch/x86/kernel/vm86_32.c | 4 +-
arch/x86/math-emu/get_address.c | 6 +---
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 3c601f8..bb70e39 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 f51a3dd..39b0aac 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 52948df..4955165 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 c223837..72082d3 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 eccfb58..317d956 100644
--- a/arch/x86/kernel/process_32.c
+++ b/arch/x86/kernel/process_32.c
@@ -129,7 +129,7 @@ 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);
@@ -302,7 +302,7 @@ 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))) {
@@ -340,7 +340,7 @@ 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 0a5df5f..508b6b5 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 40e089b..b2f977e 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 4eeb5cf..55ea30d 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 420b3b6..6ef5e99 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);
--
1.6.0.2