* Peter Zijlstra <pet...@infradead.org> wrote:
> On Tue, Jan 09, 2018 at 10:24:55AM -0500, Vince Weaver wrote:
> > On Tue, 9 Jan 2018, Peter Zijlstra wrote:
> >
> > > > I'll try your patch and see if it makes a difference.
> > >
> > > I suspect not, it shouldn't be PTI specific.
> >
> > yes, applying your patch didn't help, still locks up on the Haswell
> > machine.
>
> So CONFIG_PAGE_TABLE_ISOLATION=y and booting with "pti=off" makes it
> 'work', right?
>
> > Is there any debugging I could turn on that would help? I tried KASAN
> > but it didn't help. I think I have the regular lockdep stuff enabled.
> >
> > alt-sysrq doesn't work either (or at least, the version using BREAK over
> > the serial console doesn't, I can maybe try hooking up a keyboard/display
> > to see if that helps).
>
> The below is always my first try to get something out of the machine,
> after that its printk() stuffing code to see how far we get..
>
> In particular I'd start instrumenting the NMI entry_64.S code, because
> that's really the biggest difference between PTI and !PTI :/ all rather
> bothersome I'm afraid.
>
> Really sucks I cannot as yet reproduce.
>
> ---
> diff --git a/Documentation/admin-guide/kernel-parameters.txt
> b/Documentation/admin-guide/kernel-parameters.txt
> index 5e486b6509e5..fc9021fd6e3c 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -1172,6 +1172,11 @@
> parameter will force ia64_sal_cache_flush to call
> ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
>
> + force_early_printk
> + Forcefully uses early_console (as per earlyprintk=)
> + usage for regular printk, bypassing everything,
> + including the syslog (dmesg will be empty).
BTW., this looks very useful - please consider pushing it upstream if it does
not
hurt any of the other syslog usecases.
Thanks,
Ingo
