linux-kernel - Re: [PATCH v2] x86/mm/pti: in pti_clone

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Message-ID: <20190821103010.GJ2386@hirez.programming.kicks-ass.net>
Date:   Wed, 21 Aug 2019 12:30:10 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Song Liu <songliubraving@...com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        kernel-team@...com, stable@...r.kernel.org,
        Joerg Roedel <jroedel@...e.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>
Subject: Re: [PATCH v2] x86/mm/pti: in pti_clone_pgtable(), increase addr
 properly

On Wed, Aug 21, 2019 at 12:10:08PM +0200, Peter Zijlstra wrote:
> On Tue, Aug 20, 2019 at 01:23:14PM -0700, Song Liu wrote:

> > host-5.2-after # grep "x  pmd" /sys/kernel/debug/page_tables/dump_pid
> > 0x0000000000600000-0x0000000000e00000           8M USR ro         PSE         x  pmd
> > 0xffffffff81000000-0xffffffff81e00000          14M     ro         PSE     GLB x  pmd
> > 
> > So after this patch, the 5.2 based kernel has 7 PMDs instead of 1 PMD
> > in 4.16 kernel.
> 
> This basically gives rise to more questions than it provides answers.
> You seem to have 'forgotten' to provide the equivalent mappings on the
> two older kernels. The fact that they're not PMD is evident, but it
> would be very good to know what is mapped, and what -- if anything --
> lives in the holes we've (accidentally) created.
> 
> Can you please provide more complete mappings? Basically provide the
> whole cpu_entry_area mapping.

I tried on my local machine and:

  cat /debug/page_tables/kernel | awk '/^---/ { p=0 } /CPU entry/ { p=1 } { if (p) print $0 }' > ~/cea-{before,after}.txt

resulted in _identical_ files ?!?!

Can you share your before and after dumps?