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.
> 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).
> 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.
--
Ben Hutchings
This sentence contradicts itself - no actually it doesn't.
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