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[PATCH] i386: Use %gs as the PDA base-segment in the kernel

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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>
This commit is contained in:
Jeremy Fitzhardinge
2006-12-07 02:14:02 +01:00
committed by Andi Kleen
parent 6211119580
commit f95d47caae
10 changed files with 117 additions and 50 deletions
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26
arch/i386/kernel/process.c
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@@ -56,6 +56,7 @@
#include <asm/tlbflush.h>
#include <asm/cpu.h>
#include <asm/pda.h>
asmlinkage void ret_from_fork(void) __asm__("ret_from_fork");
@@ -346,6 +347,7 @@ int kernel_thread(int (*fn)(void *), void * arg, unsigned long flags)
regs.xds = __USER_DS;
regs.xes = __USER_DS;
regs.xgs = __KERNEL_PDA;
regs.orig_eax = -1;
regs.eip = (unsigned long) kernel_thread_helper;
regs.xcs = __KERNEL_CS | get_kernel_rpl();
@@ -431,7 +433,6 @@ int copy_thread(int nr, unsigned long clone_flags, unsigned long esp,
p->thread.eip = (unsigned long) ret_from_fork;
savesegment(fs,p->thread.fs);
savesegment(gs,p->thread.gs);
tsk = current;
if (unlikely(test_tsk_thread_flag(tsk, TIF_IO_BITMAP))) {
@@ -659,16 +660,16 @@ struct task_struct fastcall * __switch_to(struct task_struct *prev_p, struct tas
load_esp0(tss, next);
/*
* Save away %fs and %gs. No need to save %es and %ds, as
* those are always kernel segments while inside the kernel.
* Doing this before setting the new TLS descriptors avoids
* the situation where we temporarily have non-reloadable
* segments in %fs and %gs. This could be an issue if the
* NMI handler ever used %fs or %gs (it does not today), or
* if the kernel is running inside of a hypervisor layer.
* Save away %fs. No need to save %gs, as it was saved on the
* stack on entry. No need to save %es and %ds, as those are
* always kernel segments while inside the kernel. Doing this
* before setting the new TLS descriptors avoids the situation
* where we temporarily have non-reloadable segments in %fs
* and %gs. This could be an issue if the NMI handler ever
* used %fs or %gs (it does not today), or if the kernel is
* running inside of a hypervisor layer.
*/
savesegment(fs, prev->fs);
savesegment(gs, prev->gs);
/*
* Load the per-thread Thread-Local Storage descriptor.
@@ -676,16 +677,13 @@ struct task_struct fastcall * __switch_to(struct task_struct *prev_p, struct tas
load_TLS(next, cpu);
/*
* Restore %fs and %gs if needed.
* Restore %fs if needed.
*
* Glibc normally makes %fs be zero, and %gs is one of
* the TLS segments.
* Glibc normally makes %fs be zero.
*/
if (unlikely(prev->fs | next->fs))
loadsegment(fs, next->fs);
if (prev->gs | next->gs)
loadsegment(gs, next->gs);
/*
* Restore IOPL if needed.