[PATCH] i386: Convert i386 PDA code to use %fs

Convert the PDA code to use %fs rather than %gs as the segment for
per-processor data.  This is because some processors show a small but
measurable performance gain for reloading a NULL segment selector (as %fs
generally is in user-space) versus a non-NULL one (as %gs generally is).

On modern processors the difference is very small, perhaps undetectable.
Some old AMD "K6 3D+" processors are noticably slower when %fs is used
rather than %gs; I have no idea why this might be, but I think they're
sufficiently rare that it doesn't matter much.

This patch also fixes the math emulator, which had not been adjusted to
match the changed struct pt_regs.

[frederik.deweerdt@gmail.com: fixit with gdb]
[mingo@elte.hu: Fix KVM too]

Signed-off-by: Jeremy Fitzhardinge <jeremy@xensource.com>
Signed-off-by: Andi Kleen <ak@suse.de>
Cc: Ian Campbell <Ian.Campbell@XenSource.com>
Acked-by: Ingo Molnar <mingo@elte.hu>
Acked-by: Zachary Amsden <zach@vmware.com>
Cc: Eric Dumazet <dada1@cosmosbay.com>
Signed-off-by: Frederik Deweerdt <frederik.deweerdt@gmail.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>

1 files changed, 17 insertions, 16 deletions

diff --git a/arch/i386/kernel/vm86.c b/arch/i386/kernel/vm86.c
index be2f96e67f78..d1b8f2b7aea6 100644
--- a/arch/i386/kernel/vm86.c
+++ b/arch/i386/kernel/vm86.c
@@ -96,12 +96,12 @@ static int copy_vm86_regs_to_user(struct vm86_regs __user *user,
 {
         int ret = 0;
 
-        /* kernel_vm86_regs is missing xfs, so copy everything up to
-           (but not including) xgs, and then rest after xgs. */
-        ret += copy_to_user(user, regs, offsetof(struct kernel_vm86_regs, pt.xgs));
-        ret += copy_to_user(&user->__null_gs, &regs->pt.xgs,
+        /* kernel_vm86_regs is missing xgs, so copy everything up to
+           (but not including) orig_eax, and then rest including orig_eax. */
+        ret += copy_to_user(user, regs, offsetof(struct kernel_vm86_regs, pt.orig_eax));
+        ret += copy_to_user(&user->orig_eax, &regs->pt.orig_eax,
                             sizeof(struct kernel_vm86_regs) -
-                            offsetof(struct kernel_vm86_regs, pt.xgs));
+                            offsetof(struct kernel_vm86_regs, pt.orig_eax));
 
         return ret;
 }
@@ -113,12 +113,13 @@ static int copy_vm86_regs_from_user(struct kernel_vm86_regs *regs,
 {
         int ret = 0;
 
-        ret += copy_from_user(regs, user, offsetof(struct kernel_vm86_regs, pt.xgs));
-        ret += copy_from_user(&regs->pt.xgs, &user->__null_gs,
+        /* copy eax-xfs inclusive */
+        ret += copy_from_user(regs, user, offsetof(struct kernel_vm86_regs, pt.orig_eax));
+        /* copy orig_eax-__gsh+extra */
+        ret += copy_from_user(&regs->pt.orig_eax, &user->orig_eax,
                               sizeof(struct kernel_vm86_regs) -
-                              offsetof(struct kernel_vm86_regs, pt.xgs) +
+                              offsetof(struct kernel_vm86_regs, pt.orig_eax) +
                               extra);
-
         return ret;
 }
 
@@ -157,8 +158,8 @@ struct pt_regs * fastcall save_v86_state(struct kernel_vm86_regs * regs)
 
         ret = KVM86->regs32;
 
-        loadsegment(fs, current->thread.saved_fs);
-        ret->xgs = current->thread.saved_gs;
+        ret->xfs = current->thread.saved_fs;
+        loadsegment(gs, current->thread.saved_gs);
 
         return ret;
 }
@@ -285,9 +286,9 @@ static void do_sys_vm86(struct kernel_vm86_struct *info, struct task_struct *tsk
  */
         info->regs.pt.xds = 0;
         info->regs.pt.xes = 0;
-        info->regs.pt.xgs = 0;
+        info->regs.pt.xfs = 0;
 
-/* we are clearing fs later just before "jmp resume_userspace",
+/* we are clearing gs later just before "jmp resume_userspace",
  * because it is not saved/restored.
  */
 
@@ -321,8 +322,8 @@ static void do_sys_vm86(struct kernel_vm86_struct *info, struct task_struct *tsk
  */
         info->regs32->eax = 0;
         tsk->thread.saved_esp0 = tsk->thread.esp0;
-        savesegment(fs, tsk->thread.saved_fs);
-        tsk->thread.saved_gs = info->regs32->xgs;
+        tsk->thread.saved_fs = info->regs32->xfs;
+        savesegment(gs, tsk->thread.saved_gs);
 
         tss = &per_cpu(init_tss, get_cpu());
         tsk->thread.esp0 = (unsigned long) &info->VM86_TSS_ESP0;
@@ -342,7 +343,7 @@ static void do_sys_vm86(struct kernel_vm86_struct *info, struct task_struct *tsk
         __asm__ __volatile__(
                 "movl %0,%%esp\n\t"
                 "movl %1,%%ebp\n\t"
-                "mov  %2, %%fs\n\t"
+                "mov  %2, %%gs\n\t"
                 "jmp resume_userspace"
                 : /* no outputs */
                 :"r" (&info->regs), "r" (task_thread_info(tsk)), "r" (0));