x86-32: use non-lazy io bitmap context switching

Impact: remove 32-bit optimization to prepare unification

x86-32 and -64 differ in the way they context-switch tasks
with io permission bitmaps.  x86-64 simply copies the next
tasks io bitmap into place (if any) on context switch.  x86-32
invalidates the bitmap on context switch, so that the next
IO instruction will fault; at that point it installs the
appropriate IO bitmap.

This makes context switching IO-bitmap-using tasks a bit more
less expensive, at the cost of making the next IO instruction
slower due to the extra fault.  This tradeoff only makes sense
if IO-bitmap-using processes are relatively common, but they
don't actually use IO instructions very often.

However, in a typical desktop system, the only process likely
to be using IO bitmaps is the X server, and nothing at all on
a server.  Therefore the lazy context switch doesn't really win
all that much, and its just a gratuitious difference from
64-bit code.

This patch removes the lazy context switch, with a view to
unifying this code in a later change.

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 0 insertions, 46 deletions

diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index c05430ac1b44..a1d288327ff0 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -118,47 +118,6 @@ die_if_kernel(const char *str, struct pt_regs *regs, long err)
         if (!user_mode_vm(regs))
                 die(str, regs, err);
 }
-
-/*
- * Perform the lazy TSS's I/O bitmap copy. If the TSS has an
- * invalid offset set (the LAZY one) and the faulting thread has
- * a valid I/O bitmap pointer, we copy the I/O bitmap in the TSS,
- * we set the offset field correctly and return 1.
- */
-static int lazy_iobitmap_copy(void)
-{
-        struct thread_struct *thread;
-        struct tss_struct *tss;
-        int cpu;
-
-        cpu = get_cpu();
-        tss = &per_cpu(init_tss, cpu);
-        thread = &current->thread;
-
-        if (tss->x86_tss.io_bitmap_base == INVALID_IO_BITMAP_OFFSET_LAZY &&
-            thread->io_bitmap_ptr) {
-                memcpy(tss->io_bitmap, thread->io_bitmap_ptr,
-                       thread->io_bitmap_max);
-                /*
-                 * If the previously set map was extending to higher ports
-                 * than the current one, pad extra space with 0xff (no access).
-                 */
-                if (thread->io_bitmap_max < tss->io_bitmap_max) {
-                        memset((char *) tss->io_bitmap +
-                                thread->io_bitmap_max, 0xff,
-                                tss->io_bitmap_max - thread->io_bitmap_max);
-                }
-                tss->io_bitmap_max = thread->io_bitmap_max;
-                tss->x86_tss.io_bitmap_base = IO_BITMAP_OFFSET;
-                tss->io_bitmap_owner = thread;
-                put_cpu();
-
-                return 1;
-        }
-        put_cpu();
-
-        return 0;
-}
 #endif
 
 static void __kprobes
@@ -309,11 +268,6 @@ do_general_protection(struct pt_regs *regs, long error_code)
         conditional_sti(regs);
 
 #ifdef CONFIG_X86_32
-        if (lazy_iobitmap_copy()) {
-                /* restart the faulting instruction */
-                return;
-        }
-
         if (regs->flags & X86_VM_MASK)
                 goto gp_in_vm86;
 #endif