linux-kernel - Re: [PATCH] x86_64,xen,espfix: Initialize espfix on secondary CPUs

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Date:	Tue, 15 Jul 2014 08:54:53 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Boris Ostrovsky <boris.ostrovsky@...cle.com>
Cc:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	stable <stable@...r.kernel.org>
Subject: Re: [PATCH] x86_64,xen,espfix: Initialize espfix on secondary CPUs

On Tue, Jul 15, 2014 at 8:45 AM, Boris Ostrovsky
<boris.ostrovsky@...cle.com> wrote:
> On 07/15/2014 11:38 AM, Konrad Rzeszutek Wilk wrote:
>>
>> On Tue, Jul 15, 2014 at 08:26:41AM -0700, Andy Lutomirski wrote:
>>>
>>> Xen doesn't call start_secondary.
>>
>> Duh!
>>>
>>> Cc: stable@...r.kernel.org
>>> Signed-off-by: Andy Lutomirski <luto@...capital.net>
>>> ---
>>>
>>> espfix still doesn't seem to work on Xen (it goes boom in some way that
>>> I don't understand right now), but initializing all CPUs instead of just
>>> one of them seems like a good start.
>>>
>>> ISTM the right fix is probably to shove the espfix logic into
>>> native_iret and to tweak the paravirt logic so that native_iret always
>>> gets invoked.  I suspect that Xen will need its own implementation of
>>> espfix64 in the hypervisor and that, ultimately, someone may want to
>>> stop initializing espfix64 at all on Xen guests.
>>
>> I think just disallowing would be preferrable.
>
>
> I've been looking at sigreturn_64 and it seems to be crashing dom0 (with
> both mine and your patches). In kprobe_int3_handler().

You need:

http://lkml.kernel.org/g/c4e339882c121aa76254f2adde3fcbdf502faec2.1405099506.git.luto@amacapital.net

The newer version of sigreturn_32 that I pushed is a much better test
-- it tests the 64-bit cases (yay thunks!) and works on kernels
without my SS sigcontext fix.

--Andy
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