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

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Date:	Tue, 15 Jul 2014 12:05:19 -0400
From:	Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:	Andy Lutomirski <luto@...capital.net>
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 07/15/2014 11:54 AM, Andy Lutomirski wrote:
> 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.

Yes, that does it. At least we don't have yet another failure mode with 
this, which was the biggest concern.

Thanks.

-boris

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