linux-kernel - Re: 32-bit PTI with THP = userspace corruption

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Message-ID: <alpine.DEB.2.21.1809081223450.1402@nanos.tec.linutronix.de>
Date:   Sat, 8 Sep 2018 12:24:10 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Joerg Roedel <jroedel@...e.de>
cc:     Meelis Roos <mroos@...ux.ee>,
        Linux Kernel list <linux-kernel@...r.kernel.org>,
        linux-mm@...ck.org
Subject: Re: 32-bit PTI with THP = userspace corruption


On Fri, 31 Aug 2018, Joerg Roedel wrote:

> On Fri, Aug 31, 2018 at 07:12:44AM +0300, Meelis Roos wrote:
> > > Thanks for the report! I'll try to reproduce the problem tomorrow and
> > > investigate it. Can you please check if any of the kernel configurations
> > > that show the bug has CONFIG_X86_PAE set? If not, can you please test
> > > if enabling this option still triggers the problem?
> > 
> > Will check, but out of my memery there were 2 G3 HP Proliants that did 
> > not fit into the pattern (problem did not appear). I have more than 4G 
> > RAM in those and HIGHMEM_4G there, maybe that's it?
> 
> Yeah, I thought a bit about it, and for legacy paging the PMD paging
> level is the root-level where we do the mirroring between kernel and
> user page-table for PTI. This means we also need to collect A/D bits
> from both entries, which we don't do yet.
> 
> But that all means it shouldn't happen with CONFIG_X86_PAE=y.
> 
> I'll try to reproduce and work on a fix.

Any progress on this?

Thanks,

	tglx