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Date:   Wed, 20 Dec 2017 17:26:20 +0100
From:   Juergen Gross <>
To:     Thomas Gleixner <>,
        Ingo Molnar <>
Cc:     Peter Zijlstra <>,
        Dave Hansen <>,
        LKML <>,,
        Linus Torvalds <>,
        Andy Lutomirsky <>,
        Borislav Petkov <>,
        Greg KH <>,,, Brian Gerst <>,
        Josh Poimboeuf <>,
        Denys Vlasenko <>,
        Rik van Riel <>,
        Boris Ostrovsky <>,
        David Laight <>,
        Eduardo Valentin <>,,
        Will Deacon <>,,
        Dave Hansen <>,
        Borislav Petkov <>, "H. Peter Anvin" <>
Subject: Re: [patch V163 27/51] x86/mm/pti: Populate user PGD

On 20/12/17 01:22, Thomas Gleixner wrote:
> On Tue, 19 Dec 2017, Thomas Gleixner wrote:
>> On Tue, 19 Dec 2017, Ingo Molnar wrote:
>> We don't run out of space, but the 0-day robot triggered a nasty issue.
>> The fixmap bottom address, which contains the early_ioremap fixmap area, is:
>> If that address is lower than:
>>     vaddr_end = __START_KERNEL_map + KERNEL_IMAGE_SIZE;
>> then cleanup_highmap() will happily 0 out the PMD entry for the PTE page of
>> FIX_BTMAP. That entry was set up earlier in early_ioremap_init().
>> As a consequence the first call to __early_set_fixmap() which tries to
>> install a PTE for early_ioremap() will crash and burn.
>> Below is a nasty hack which fixes the problem. Ideally we get all of this
>> cpu_entry_stuff out of the fixmap. I'll look into that later, but for now
>> the patch 'fixes' the issue.
> I had a stab on moving the cpu_entry_area to some other place.
> The patch below works, but:
>  - it breaks i386 build because I have not yet found a way to place the
>    CPU_ENTRY_AREA_BASE without creating include recursion hell
>  - it probably does not work on XEN_PV, but I'm too tired now to figure
>    that out.

The attached patch lets the system come up as XEN_PV.


View attachment "vsyscall.patch" of type "text/x-patch" (992 bytes)

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