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authorZachary Amsden <zach@vmware.com>2005-09-03 15:56:39 -0700
committerLinus Torvalds <torvalds@evo.osdl.org>2005-09-05 00:06:11 -0700
commite7a2ff593c0e48b130434dee4d2fd3452a850e6f (patch)
tree89bca4c0a0818d1e217c76866f62c1b133a425d7
parent2f2984eb4afb2a4298e3186cb49cc7e88dd6d929 (diff)
[PATCH] i386: load_tls() fix
Subtle fix: load_TLS has been moved after saving %fs and %gs segments to avoid creating non-reversible segments. This could conceivably cause a bug if the kernel ever needed to save and restore fs/gs from the NMI handler. It currently does not, but this is the safest approach to avoiding fs/gs corruption. SMIs are safe, since SMI saves the descriptor hidden state. Signed-off-by: Zachary Amsden <zach@vmware.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
-rw-r--r--arch/i386/kernel/process.c19
1 files changed, 12 insertions, 7 deletions
diff --git a/arch/i386/kernel/process.c b/arch/i386/kernel/process.c
index 761d4ed47ef..9d94995e967 100644
--- a/arch/i386/kernel/process.c
+++ b/arch/i386/kernel/process.c
@@ -678,21 +678,26 @@ struct task_struct fastcall * __switch_to(struct task_struct *prev_p, struct tas
__unlazy_fpu(prev_p);
/*
- * Reload esp0, LDT and the page table pointer:
+ * Reload esp0.
*/
load_esp0(tss, next);
/*
- * Load the per-thread Thread-Local Storage descriptor.
+ * 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.
*/
- load_TLS(next, cpu);
+ savesegment(fs, prev->fs);
+ savesegment(gs, prev->gs);
/*
- * Save away %fs and %gs. No need to save %es and %ds, as
- * those are always kernel segments while inside the kernel.
+ * Load the per-thread Thread-Local Storage descriptor.
*/
- asm volatile("mov %%fs,%0":"=m" (prev->fs));
- asm volatile("mov %%gs,%0":"=m" (prev->gs));
+ load_TLS(next, cpu);
/*
* Restore %fs and %gs if needed.