[PATCH] i386: Use %gs as the PDA base-segment in the kernel
This patch is the meat of the PDA change. This patch makes several related
changes:
1: Most significantly, %gs is now used in the kernel. This means that on
entry, the old value of %gs is saved away, and it is reloaded with
__KERNEL_PDA.
2: entry.S constructs the stack in the shape of struct pt_regs, and this
is passed around the kernel so that the process's saved register
state can be accessed.
Unfortunately struct pt_regs doesn't currently have space for %gs
(or %fs). This patch extends pt_regs to add space for gs (no space
is allocated for %fs, since it won't be used, and it would just
complicate the code in entry.S to work around the space).
3: Because %gs is now saved on the stack like %ds, %es and the integer
registers, there are a number of places where it no longer needs to
be handled specially; namely context switch, and saving/restoring the
register state in a signal context.
4: And since kernel threads run in kernel space and call normal kernel
code, they need to be created with their %gs == __KERNEL_PDA.
Signed-off-by: Jeremy Fitzhardinge <jeremy@xensource.com>
Signed-off-by: Andi Kleen <ak@suse.de>
Cc: Chuck Ebbert <76306.1226@compuserve.com>
Cc: Zachary Amsden <zach@vmware.com>
Cc: Jan Beulich <jbeulich@novell.com>
Cc: Andi Kleen <ak@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
diff --git a/include/asm-i386/processor.h b/include/asm-i386/processor.h
index a9f2041..f73cf83 100644
--- a/include/asm-i386/processor.h
+++ b/include/asm-i386/processor.h
@@ -473,6 +473,7 @@
.vm86_info = NULL, \
.sysenter_cs = __KERNEL_CS, \
.io_bitmap_ptr = NULL, \
+ .gs = __KERNEL_PDA, \
}
/*
@@ -500,7 +501,8 @@
}
#define start_thread(regs, new_eip, new_esp) do { \
- __asm__("movl %0,%%fs ; movl %0,%%gs": :"r" (0)); \
+ __asm__("movl %0,%%fs": :"r" (0)); \
+ regs->xgs = 0; \
set_fs(USER_DS); \
regs->xds = __USER_DS; \
regs->xes = __USER_DS; \