linux-kernel - Re: [PATCH 4.14 023/159] mm/sparsemem: Allocate mem_section at runtime for CONFIG_SPARSEMEM

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Date:   Thu, 25 Jan 2018 18:50:44 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Baoquan He <bhe@...hat.com>
Cc:     Ingo Molnar <mingo@...nel.org>, Mike Galbraith <efault@....de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Dave Young <dyoung@...hat.com>, kexec@...ts.infradead.org,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Andy Lutomirski <luto@...capital.net>, linux-mm@...ck.org,
        Vivek Goyal <vgoyal@...hat.com>,
        Cyrill Gorcunov <gorcunov@...nvz.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...e.de>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: Re: [PATCH 4.14 023/159] mm/sparsemem: Allocate mem_section at
 runtime for CONFIG_SPARSEMEM_EXTREME=y

On Wed, Jan 17, 2018 at 01:24:54PM +0800, Baoquan He wrote:
> Hi Kirill,
> 
> I setup qemu 2.9.0 to test 5-level on kexec/kdump support. While both
> kexec and kdump reset to BIOS immediately after triggering. I saw your
> patch adding 5-level paging support for kexec. Wonder if your test
> succeeded to jump into kexec/kdump kernel, and what else I need to
> make it. By the way, I just tested the latest upstream kernel.
> 
> commit 7f6890418 x86/kexec: Add 5-level paging support
> 
> [ ~]$ qemu-system-x86_64 --version
> QEMU emulator version 2.9.0(qemu-2.9.0-1.fc26.1)
> Copyright (c) 2003-2017 Fabrice Bellard and the QEMU Project developers

Sorry for delay.

I didn't tested it in 5-level paging mode :-/

The patch below helps in my case. Could you test it?

diff --git a/arch/x86/kernel/relocate_kernel_64.S b/arch/x86/kernel/relocate_kernel_64.S
index 307d3bac5f04..65a98cf2307d 100644
--- a/arch/x86/kernel/relocate_kernel_64.S
+++ b/arch/x86/kernel/relocate_kernel_64.S
@@ -126,8 +126,12 @@ identity_mapped:
        /*
         * Set cr4 to a known state:
         *  - physical address extension enabled
+        *  - 5-level paging, if enabled
         */
        movl    $X86_CR4_PAE, %eax
+#ifdef CONFIG_X86_5LEVEL
+       orl     $X86_CR4_LA57, %eax
+#endif
        movq    %rax, %cr4

        jmp 1f
-- 
 Kirill A. Shutemov