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Subject[PATCH] x86/extable: Add a comment about early exception handlers
Date
Borislav asked for a comment explaining why all exception handlers are
allowed early.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
---
arch/x86/mm/extable.c | 14 ++++++++++++++
1 file changed, 14 insertions(+)

diff --git a/arch/x86/mm/extable.c b/arch/x86/mm/extable.c
index 98b5f45d9d79..36fe03bc81ee 100644
--- a/arch/x86/mm/extable.c
+++ b/arch/x86/mm/extable.c
@@ -132,6 +132,20 @@ void __init early_fixup_exception(struct pt_regs *regs, int trapnr)
if (regs->cs != __KERNEL_CS)
goto fail;

+ /*
+ * The full exception fixup machinery is available as soon as
+ * the early IDT is loaded. This means that it is the
+ * responsibility of extable users to either function correctly
+ * when handlers are invoked early or to simply avoid causing
+ * exceptions before they're ready to handle them.
+ *
+ * This is better than filtering which handlers can be used,
+ * because refusing to call a handler here is guaranteed to
+ * result in a hard-to-debug panic.
+ *
+ * Keep in mind that not all vectors actually get here. Early
+ * fage faults, for example, are special.
+ */
if (fixup_exception(regs, trapnr))
return;

--
2.5.5
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