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'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')
I've backported 375074cc736a to 3.13 which seems to fix this particular
issue but I'm still seeing userspace segfaults.
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.
...Juerg
> Using the 'nopcid' kernel parameter gets it to boot but it's somewhat
> unstable even after that - once I start another kernel build I see
> programs segfaulting. So I'm guessing I've screwed up some of the TLB
> stuff.
>
> I'm going to continue investigating this myself before making a
> release, but would really appreciate any time people can spare to
> review this patch series.
>
> (I haven't found any such regression in 3.2.98.)
>
> Ben.
>
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