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x86: remove open-coded save/load segment operations

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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>
This commit is contained in:
Jeremy Fitzhardinge 2008-06-25 00:19:00 -04:00 committed by Ingo Molnar
parent af2b1c609f
commit ada8570823
2 changed files with 17 additions and 14 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

3
arch/x86/kernel/cpu/common_64.c
View File

@ -480,7 +480,8 @@ void pda_init(int cpu)
struct x8664_pda *pda = cpu_pda(cpu);
/* Setup up data that may be needed in __get_free_pages early */
asm volatile("movl %0,%%fs ; movl %0,%%gs" :: "r" (0));
loadsegment(fs, 0);
loadsegment(gs, 0);
/* Memory clobbers used to order PDA accessed */
mb();
wrmsrl(MSR_GS_BASE, pda);

28
arch/x86/kernel/process_64.c
View File

@ -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