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Subject: Re: [RFC PATCH] x86_64/mm/boot: Fix kernel_ident_mapping_init()
 failure for kexec
References: <1489990291-2252-1-git-send-email-xlpang@redhat.com>
 <20170324120458.nw3fwpmdptjtj5qb@node.shutemov.name>
 <58DCEA40.7040102@redhat.com>
To: "Kirill A. Shutemov" <kirill@shutemov.name>,
        Xunlei Pang <xlpang@redhat.com>, Ingo Molnar <mingo@redhat.com>
Cc: x86@kernel.org, kexec@lists.infradead.org,
        linux-kernel@vger.kernel.org,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
From: Xunlei Pang <xpang@redhat.com>
Message-ID: <58DCFD55.8060602@redhat.com>
Date: Thu, 30 Mar 2017 20:43:01 +0800
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On 03/30/2017 at 07:21 PM, Xunlei Pang wrote:
> On 03/24/2017 at 08:04 PM, Kirill A. Shutemov wrote:
>> On Mon, Mar 20, 2017 at 02:11:31PM +0800, Xunlei Pang wrote:
>>> I found that the kdump is broken on linux-4.11.0-rc2+
>> That's actually tip tree or linux-next. The problematic change is not in
>> Linus' tree.
>>
>>> , probably
>>> due to the 5level-paging feature that "#define p4d_present(p4d) 1",
>>> as a result in ident_p4d_init(), it will go into ident_pud_init()
>>> directly without allocating the new pud.
>>>
>>> Looks like this patch can make it work again.
>> Okay, that's bisectability issue. Uncovered by splitting my patchset into
>> parts.
>>
>> Could you check if applying "Part 2" of 5-level paging changes[1] would
>> help you?
> I confirmed that it works after applying your following patches:
>   x86: Convert the rest of the code to support p4d_t

To be exact, this one("x86: Convert the rest of the code to support p4d_t") fixes the issue.

>   x86/xen: Change __xen_pgd_walk() and xen_cleanmfnmap() to support p4d
>   x86/kasan: Prepare clear_pgds() to switch to <asm-generic/pgtable-nop4d.h>
>   x86/mm/pat: Add 5-level paging support
>   x86/efi: Add 5-level paging support
>   x86/kexec: Add 5-level paging support
>
> Regards,
> Xunlei
>
>> Making the code work with both <asm-generic/5level-fixup.h> and
>> <asm-generic/pgtable-nop4d.h> would make it even uglier. Not sure if it
>> makes sense to address it on its own if second part fixes the situation.
>>
>> [1] http://lkml.kernel.org/r/20170317185515.8636-1-kirill.shutemov@linux.intel.com
>>
>
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