Re: [tip:x86/pti] x86/speculation: Use IBRS if available before calling into firmware

[Peter Zijlstra]

On Sat, Feb 17, 2018 at 11:26:16AM +0100, Ingo Molnar wrote:
> Note that PeterZ was struggling with intermittent boot hangs yesterday as well, 
> which hangs came and went during severeal (fruitless) bisection attempts. Then at 
> a certain point the hangs went away altogether.
> 
> The symptoms for both his and your hangs are consistent with an alignment 
> dependent bug.

Mine would consistently hang right after

  "Freeing SMP alternatives memory: 44K"

At one point I bisected it to commit:

  a06cc94f3f8d ("x86/build: Drop superfluous ALIGN from the linker script")

But shortly thereafter I started having trouble reproducing, and now I
can run kernels that before would consistently fail to boot :/

> My other guess is that it's perhaps somehow microcode related?

I did not update or otherwise change packages while I was bisecting; the
machine is:

vendor_id       : GenuineIntel
cpu family      : 6
model           : 62
model name      : Intel(R) Xeon(R) CPU E5-2680 v2 @ 2.80GHz
stepping        : 4
microcode       : 0x428

Like I wrote on IRC; what _seems_ to have 'cured' things is clearing out
my /boot. The amount of kernels generated by the bisect was immense and
running 'update-grub' was taking _much_ longer than actually building a
new kernel.

What I have not tried is again generating and installing that many
kernels to see if that will make it go 'funny' again.