Commit-ID: 60a0e2039e3df6c0a2b896bd78af36ff36fb629c Gitweb: http://git.kernel.org/tip/60a0e2039e3df6c0a2b896bd78af36ff36fb629c Author: Andy Lutomirski <luto@xxxxxxxxxx> AuthorDate: Mon, 4 Apr 2016 08:46:22 -0700 Committer: Ingo Molnar <mingo@xxxxxxxxxx> CommitDate: Wed, 13 Apr 2016 11:37:47 +0200 x86/extable: Add a comment about early exception handlers Borislav asked for a comment explaining why all exception handlers are allowed early. Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxx> Reviewed-by: Borislav Petkov <bp@xxxxxxx> Acked-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Cc: Arjan van de Ven <arjan@xxxxxxxxxxxxxxx> Cc: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx> Cc: Borislav Petkov <bp@xxxxxxxxx> Cc: KVM list <kvm@xxxxxxxxxxxxxxx> Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Cc: xen-devel <Xen-devel@xxxxxxxxxxxxx> Link: http://lkml.kernel.org/r/5f1dcd6919f4a5923959a8065cb2c04d9dac1412.1459784772.git.luto@xxxxxxxxxx Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx> --- 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 fd9eb98..aaeda3f 100644 --- a/arch/x86/mm/extable.c +++ b/arch/x86/mm/extable.c @@ -125,6 +125,20 @@ 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; -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
