commit 464d1a78fbf8cf6c7fd970e7b3e2db50a320ce28
author Jeremy Fitzhardinge <jeremy@goop.org> Tue Feb 13 13:26:20 2007 +0100
committer Andi Kleen <andi@basil.nowhere.org> Tue Feb 13 13:26:20 2007 +0100
tree 536d8a92976e675b484b35dec88d40c97fab8ac8
parent 54413927f022292aeccadd268fbf1c0b42129945

[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>

arch/i386/kernel/vm86.c

diff --git a/arch/i386/kernel/vm86.c b/arch/i386/kernel/vm86.c
index be2f96e..d1b8f2b 100644
--- a/arch/i386/kernel/vm86.c
+++ b/arch/i386/kernel/vm86.c
@@ -96,12 +96,12 @@
 {
 	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 @@
 {
 	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 @@
 
 	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 @@
  */
 	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 @@
  */
 	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 @@
 	__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));