linux-kernel - Re: [RFC PATCH] arm64: fix the missing ktpi= cmdline check in arm64_kernel_unmapped_at

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Date:   Wed, 18 Mar 2020 20:13:00 +0000
From:   Will Deacon <will@...nel.org>
To:     Mark Brown <broonie@...nel.org>
Cc:     Mark Rutland <mark.rutland@....com>,
        Hongbo Yao <yaohongbo@...wei.com>,
        linux-kernel@...r.kernel.org, catalin.marinas@....com,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [RFC PATCH] arm64: fix the missing ktpi= cmdline check in
 arm64_kernel_unmapped_at_el0()

On Wed, Mar 18, 2020 at 11:32:17AM +0000, Mark Brown wrote:
> On Tue, Mar 17, 2020 at 09:01:54PM +0000, Will Deacon wrote:
> > On Tue, Mar 17, 2020 at 04:36:38PM +0000, Mark Brown wrote:
> 
> > > I'd need to go back and retest to confirm but it looks like always had
> > > the issue that we'd install some nG mappings early even with KPTI
> > > disabled on the command line so your change is just restoring the
> > > previous behaviour and we're no worse than we were before.
> 
> > Urgh, this code brings back really bad memories :( :( :(
> 
> Tell me about it.
> 
> > So I've hacked the following, which appears to work but damn I'd like
> > somebody else to look at this. I also have a nagging feeling that you
> > implemented it like this at some point, but we tried to consolidate things
> > during review.
> 
> > Thoughts?
> 
> I don't think I did *exactly* this but it's familiar yeah.  It looks
> sensible and I can't think of any problems but that doesn't mean there
> aren't any.

Well, thanks for having a look!

Hongbo -- please can you confirm that this fixes the problem that you are
seeing?

Will