x86: save %fs and %gs before load_TLS() and arch_leave_lazy_cpu_mode()

We must do this because load_TLS() may need to clear %fs and %gs.
(e.g. under Xen).

Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
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, 11 insertions, 6 deletions

diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
index 488eaca47bd8..db5eb963e4df 100644
--- a/arch/x86/kernel/process_64.c
+++ b/arch/x86/kernel/process_64.c
@@ -538,6 +538,7 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p)
                                  *next = &next_p->thread;
         int cpu = smp_processor_id();
         struct tss_struct *tss = &per_cpu(init_tss, cpu);
+        unsigned fsindex, gsindex;
 
         /* we're going to use this soon, after a few expensive things */
         if (next_p->fpu_counter>5)
@@ -560,6 +561,15 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p)
         if (unlikely(next->ds | prev->ds))
                 loadsegment(ds, next->ds);
 
+
+        /* We must save %fs and %gs before load_TLS() because
+         * %fs and %gs may be cleared by load_TLS().
+         *
+         * (e.g. xen_load_tls())
+         */
+        savesegment(fs, fsindex);
+        savesegment(gs, gsindex);
+
         load_TLS(next, cpu);
 
         /*
@@ -575,8 +585,6 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p)
          * Switch FS and GS.
          */
         { 
-                unsigned 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
@@ -594,10 +602,7 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p)
                 if (next->fs) 
                         wrmsrl(MSR_FS_BASE, next->fs); 
                 prev->fsindex = fsindex;
-        }
-        { 
-                unsigned gsindex;
-                savesegment(gs, gsindex);
+
                 if (unlikely(gsindex | next->gsindex | prev->gs)) {
                         load_gs_index(next->gsindex);
                         if (gsindex)