Re: [PATCH 4.14 023/159] mm/sparsemem: Allocate mem_section at runtime for CONFIG_SPARSEMEM_EXTREME=y

[Baoquan He]

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

Thanks
Baoquan

On 01/09/18 at 03:13am, Kirill A. Shutemov wrote:
> On Mon, Jan 08, 2018 at 08:46:53PM +0300, Kirill A. Shutemov wrote:
> > On Mon, Jan 08, 2018 at 04:04:44PM +0000, Ingo Molnar wrote:
> > > 
> > > hi Kirill,
> > > 
> > > As Mike reported it below, your 5-level paging related upstream commit 
> > > 83e3c48729d9 and all its followup fixes:
> > > 
> > >  83e3c48729d9: mm/sparsemem: Allocate mem_section at runtime for CONFIG_SPARSEMEM_EXTREME=y
> > >  629a359bdb0e: mm/sparsemem: Fix ARM64 boot crash when CONFIG_SPARSEMEM_EXTREME=y
> > >  d09cfbbfa0f7: mm/sparse.c: wrong allocation for mem_section
> > > 
> > > ... still breaks kexec - and that now regresses -stable as well.
> > > 
> > > Given that 5-level paging now syntactically depends on having this commit, if we 
> > > fully revert this then we'll have to disable 5-level paging as well.
> 
> This *should* help.
> 
> Mike, could you test this? (On top of the rest of the fixes.)
> 
> Sorry for the mess.
> 
> From 100fd567754f1457be94732046aefca204c842d2 Mon Sep 17 00:00:00 2001
> From: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
> Date: Tue, 9 Jan 2018 02:55:47 +0300
> Subject: [PATCH] kdump: Write a correct address of mem_section into vmcoreinfo
> 
> Depending on configuration mem_section can now be an array or a pointer
> to an array allocated dynamically. In most cases, we can continue to refer
> to it as 'mem_section' regardless of what it is.
> 
> But there's one exception: '&mem_section' means "address of the array" if
> mem_section is an array, but if mem_section is a pointer, it would mean
> "address of the pointer".
> 
> We've stepped onto this in kdump code. VMCOREINFO_SYMBOL(mem_section)
> writes down address of pointer into vmcoreinfo, not array as we wanted.
> 
> Let's introduce VMCOREINFO_ARRAY() that would handle the situation
> correctly for both cases.
> 
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> Fixes: 83e3c48729d9 ("mm/sparsemem: Allocate mem_section at runtime for CONFIG_SPARSEMEM_EXTREME=y")
> ---
>  include/linux/crash_core.h | 2 ++
>  kernel/crash_core.c        | 2 +-
>  2 files changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/crash_core.h b/include/linux/crash_core.h
> index 06097ef30449..83ae04950269 100644
> --- a/include/linux/crash_core.h
> +++ b/include/linux/crash_core.h
> @@ -42,6 +42,8 @@ phys_addr_t paddr_vmcoreinfo_note(void);
>  	vmcoreinfo_append_str("PAGESIZE=%ld\n", value)
>  #define VMCOREINFO_SYMBOL(name) \
>  	vmcoreinfo_append_str("SYMBOL(%s)=%lx\n", #name, (unsigned long)&name)
> +#define VMCOREINFO_ARRAY(name) \
> +	vmcoreinfo_append_str("SYMBOL(%s)=%lx\n", #name, (unsigned long)name)
>  #define VMCOREINFO_SIZE(name) \
>  	vmcoreinfo_append_str("SIZE(%s)=%lu\n", #name, \
>  			      (unsigned long)sizeof(name))
> diff --git a/kernel/crash_core.c b/kernel/crash_core.c
> index b3663896278e..d4122a837477 100644
> --- a/kernel/crash_core.c
> +++ b/kernel/crash_core.c
> @@ -410,7 +410,7 @@ static int __init crash_save_vmcoreinfo_init(void)
>  	VMCOREINFO_SYMBOL(contig_page_data);
>  #endif
>  #ifdef CONFIG_SPARSEMEM
> -	VMCOREINFO_SYMBOL(mem_section);
> +	VMCOREINFO_ARRAY(mem_section);
>  	VMCOREINFO_LENGTH(mem_section, NR_SECTION_ROOTS);
>  	VMCOREINFO_STRUCT_SIZE(mem_section);
>  	VMCOREINFO_OFFSET(mem_section, section_mem_map);
> -- 
>  Kirill A. Shutemov
> 
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