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x86/extable: Add a comment about early exception handlers

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Borislav asked for a comment explaining why all exception handlers are
allowed early.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Reviewed-by: Borislav Petkov <bp@suse.de>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Arjan van de Ven <arjan@linux.intel.com>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: KVM list <kvm@vger.kernel.org>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: xen-devel <Xen-devel@lists.xen.org>
Link: http://lkml.kernel.org/r/5f1dcd6919f4a5923959a8065cb2c04d9dac1412.1459784772.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Andy Lutomirski 2016-04-04 08:46:22 -07:00 committed by Ingo Molnar
parent b828b79fcc
commit 60a0e2039e
1 changed files with 14 additions and 0 deletions
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14
arch/x86/mm/extable.c
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@ -125,6 +125,20 @@ void __init early_fixup_exception(struct pt_regs *regs, int trapnr)
if (regs->cs != __KERNEL_CS) if (regs->cs != __KERNEL_CS)
goto fail; 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)) if (fixup_exception(regs, trapnr))
return; return;