x86: remove open-coded save/load segment operations

This removes a pile of buggy open-coded implementations of savesegment
and loadsegment.

(They are buggy because they don't have memory barriers to prevent
them from being reordered with respect to memory accesses.)

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Cc: xen-devel <xen-devel@lists.xensource.com>
Cc: Stephen Tweedie <sct@redhat.com>
Cc: Eduardo Habkost <ehabkost@redhat.com>
Cc: Mark McLoughlin <markmc@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 15 insertions, 13 deletions

diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
index 290183e9731a..ddc6fcc73dc6 100644
--- a/arch/x86/kernel/process_64.c
+++ b/arch/x86/kernel/process_64.c
@@ -335,10 +335,10 @@ int copy_thread(int nr, unsigned long clone_flags, unsigned long sp,
         p->thread.fs = me->thread.fs;
         p->thread.gs = me->thread.gs;
 
-        asm("mov %%gs,%0" : "=m" (p->thread.gsindex));
-        asm("mov %%fs,%0" : "=m" (p->thread.fsindex));
-        asm("mov %%es,%0" : "=m" (p->thread.es));
-        asm("mov %%ds,%0" : "=m" (p->thread.ds));
+        savesegment(gs, p->thread.gsindex);
+        savesegment(fs, p->thread.fsindex);
+        savesegment(es, p->thread.es);
+        savesegment(ds, p->thread.ds);
 
         if (unlikely(test_tsk_thread_flag(me, TIF_IO_BITMAP))) {
                 p->thread.io_bitmap_ptr = kmalloc(IO_BITMAP_BYTES, GFP_KERNEL);
@@ -377,7 +377,9 @@ out:
 void
 start_thread(struct pt_regs *regs, unsigned long new_ip, unsigned long new_sp)
 {
-        asm volatile("movl %0, %%fs; movl %0, %%es; movl %0, %%ds" :: "r"(0));
+        loadsegment(fs, 0);
+        loadsegment(es, 0);
+        loadsegment(ds, 0);
         load_gs_index(0);
         regs->ip                = new_ip;
         regs->sp                = new_sp;
@@ -550,11 +552,11 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p)
          * Switch DS and ES.
          * This won't pick up thread selector changes, but I guess that is ok.
          */
-        asm volatile("mov %%es,%0" : "=m" (prev->es));
+        savesegment(es, prev->es);
         if (unlikely(next->es | prev->es))
                 loadsegment(es, next->es); 
-        
-        asm volatile ("mov %%ds,%0" : "=m" (prev->ds));
+
+        savesegment(ds, prev->ds);
         if (unlikely(next->ds | prev->ds))
                 loadsegment(ds, next->ds);
 
@@ -565,7 +567,7 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p)
          */
         { 
                 unsigned fsindex;
-                asm volatile("movl %%fs,%0" : "=r" (fsindex)); 
+                savesegment(fs, fsindex);
                 /* segment register != 0 always requires a reload. 
                    also reload when it has changed. 
                    when prev process used 64bit base always reload
@@ -586,7 +588,7 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p)
         }
         { 
                 unsigned gsindex;
-                asm volatile("movl %%gs,%0" : "=r" (gsindex)); 
+                savesegment(gs, gsindex);
                 if (unlikely(gsindex | next->gsindex | prev->gs)) {
                         load_gs_index(next->gsindex);
                         if (gsindex)
@@ -767,7 +769,7 @@ long do_arch_prctl(struct task_struct *task, int code, unsigned long addr)
                         set_32bit_tls(task, FS_TLS, addr);
                         if (doit) {
                                 load_TLS(&task->thread, cpu);
-                                asm volatile("movl %0,%%fs" :: "r"(FS_TLS_SEL));
+                                loadsegment(fs, FS_TLS_SEL);
                         }
                         task->thread.fsindex = FS_TLS_SEL;
                         task->thread.fs = 0;
@@ -777,7 +779,7 @@ long do_arch_prctl(struct task_struct *task, int code, unsigned long addr)
                         if (doit) {
                                 /* set the selector to 0 to not confuse
                                    __switch_to */
-                                asm volatile("movl %0,%%fs" :: "r" (0));
+                                loadsegment(fs, 0);
                                 ret = checking_wrmsrl(MSR_FS_BASE, addr);
                         }
                 }
@@ -800,7 +802,7 @@ long do_arch_prctl(struct task_struct *task, int code, unsigned long addr)
                 if (task->thread.gsindex == GS_TLS_SEL)
                         base = read_32bit_tls(task, GS_TLS);
                 else if (doit) {
-                        asm("movl %%gs,%0" : "=r" (gsindex));
+                        savesegment(gs, gsindex);
                         if (gsindex)
                                 rdmsrl(MSR_KERNEL_GS_BASE, base);
                         else