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, 6 deletions

diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index c7a98f738210..76139506c3e4 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -248,7 +248,6 @@ struct x86_hw_tss {
 #define IO_BITMAP_LONGS                 (IO_BITMAP_BYTES/sizeof(long))
 #define IO_BITMAP_OFFSET                offsetof(struct tss_struct, io_bitmap)
 #define INVALID_IO_BITMAP_OFFSET        0x8000
-#define INVALID_IO_BITMAP_OFFSET_LAZY   0x9000
 
 struct tss_struct {
         /*
@@ -263,11 +262,6 @@ struct tss_struct {
          * be within the limit.
          */
         unsigned long           io_bitmap[IO_BITMAP_LONGS + 1];
-        /*
-         * Cache the current maximum and the last task that used the bitmap:
-         */
-        unsigned long           io_bitmap_max;
-        struct thread_struct    *io_bitmap_owner;
 
         /*
          * .. and then another 0x100 bytes for the emergency kernel stack: