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Date: Fri, 5 Jan 2018 21:48:13 +0100
From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: Andy Lutomirski <luto@kernel.org>
Cc: Pavel Tatashin <pasha.tatashin@oracle.com>,
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Subject: Re: [PATCH 4.4 00/37] 4.4.110-stable review
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On Fri, Jan 05, 2018 at 10:15:00AM -0800, Andy Lutomirski wrote:
> On Fri, Jan 5, 2018 at 9:52 AM, Greg Kroah-Hartman
> <gregkh@linuxfoundation.org> wrote:
> > On Fri, Jan 05, 2018 at 12:48:54PM -0500, Pavel Tatashin wrote:
> >> Boots successfully with "noefi" kernel parameter :)
> >
> > Thanks, that will help me narrow it down.  I'll dig through more patches
> > when I get home tonight...
> 
> I wish you luck.  The 4.4 series is "KAISER", not "KPTI", and the
> relevant code is spread all over the place and is generally garbage.
> See, for example, the turd called kaiser_set_shadow_pgd().  I would
> not be terribly surprised if that particular turd is biting here.
> 
> An alternative theory is that something is screwy in the EFI code.  I
> don't see anything directly wrong, but it's certainly a bit sketchy.
> The newer kernels carefully avoid using PCID 0 for real work to avoid
> corruption due to EFI and similar things.  The "KAISER" code has no
> such mitigation.  Fortunately, it seems to use PCID=0 for kernel and
> PCID=nonzero for user, so the obvious problem isn't present, but
> something could still be wrong.
> 
> Pavel, can you send your /proc/cpuinfo on a noefi boot?  (Just the
> first CPU worth is fine.)
> 
> FWIW, I said before that I have very little desire to help debug
> "KAISER".  I stand by that.

I totally understand, and do not expect your help at all.

Worse case, I point people at 4.14 and tell them to upgrade, I'm not
going to waste a ton of time on this for the same exact reasons you list
here.

And yeah, kaiser_set_shadow_pgd() is horrid, I've already gotten sucked
into it for long enough...

greg k-h