Re: PANIC: double fault, error_code: 0x0 in 4.0.0-rc3-2, kvm related?

From: Andy Lutomirski
Date: Wed Mar 18 2015 - 18:29:39 EST

On Wed, Mar 18, 2015 at 3:28 PM, Linus Torvalds
<torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
> On Wed, Mar 18, 2015 at 3:22 PM, Jiri Kosina <jkosina@xxxxxxx> wrote:
>> But what if the GPF handler pagefaults afterwards? It'd be operating on
>> user stack already.
> So I think this might be the answer. We don't see the GP fault,
> because we don't have a backtrace, because that backtrace is on the
> user stack (which is why the stack trace dumping fails - we should
> probably fix that, btw - the second oops is just confusing and not
> helpful).
> Is the intel check for canonical address (that __VIRTUAL_MASK_SHIFT
> thing) perhaps wrong or not as strict as Intel CPU's do? We'd never
> notice in normal situations..

I explicitly tested that I could blow up the kernel if I intentionally
broke that test, and I couldn't blow it up with the test as written.
That doesn't prove it's correct, though.

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