On 01/08/2018 09:39 PM, Ben Hutchings wrote:
> On Mon, 2018-01-08 at 08:10 +0100, Juerg Haefliger wrote:
>> Ben,
>>
>> On 01/08/2018 12:35 AM, Ben Hutchings wrote:
>>> I have a backport of KPTI/KAISER to 3.16, based on Hugh Dickins's work
>>> for 3.18, some upstream changes between 3.16 and 3.18, and other
>>> patches that went into 4.4.75.
>>>
>>> I sent this out for review on the stable list after quite minimal
>>> testing, but have done more since then. On bare metal (Sandy Bridge,
>>> with pcid but not invpcid) it crashes at boot. In fact it
>>> reboots without any panic message, suggesting a triple fault, as soon
>>> as I apply the patch that turns on CR4.PCIDE, i.e. without KPTI itself.
>>
>> I've seen this as well with my 3.13 tree. As soon as PCID is set on the
>> first (non-boot) CPU, the kernel reboots. Note that it seems to work
>> fine with maxcpus=1.
>
> I see, this makes sense.
>
>> I've checked the other versions, your 3.2 doesn't have this issue and
>> Hugh's 3.18 doesn't have it either. After some bisecting, I found that
>> the problem was introduced in 3.15 by:
>> cda846f101fb ('x86, realmode: read cr4 and EFER from kernel for 64-bit
>> trampoline')
>> and then later fixed again in 4.0 by:
>> 375074cc736a ('x86: Clean up cr4 manipulation')
>
> Thanks! This plus obvious changes to the patches using
> {clear,set}_in_cr4() gets me a kernel that boots on the SNB system.
Do you have debs I could run some tests against?
>> I've backported 375074cc736a to 3.13 which seems to fix this particular
>> issue but I'm still seeing userspace segfaults.
>
> With the above changes I'm not seeing any user-space segfaults either
> (so far).
Hmm... I was hoping you did ;-) Bummer. I've added the TLB flushing
patches to 3.13 that you backported from 3.18 (plus some dependencies)
but I'm still seeing segfaults.
...Juerg
>> FWIW:
>> My tree: https://code.launchpad.net/~juergh/+git/linux-pti
>> pti/3.13 is my 3.13 tree, pti/3.2.97-bwh and pti/3.16.52-bwh are yours
>> and pti/3.18.72 is Hugh's.
>
> I've just pushed 3.16.53-rc2 to
> https://git.kernel.org/pub/scm/linux/kernel/git/bwh/linux-stable-rc.git
>
> Ben.
>
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