linux-kernel - Re: [PATCH] kexec: Export memory sections virtual addresses to vmcoreinfo

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Date:   Tue, 1 Nov 2016 13:33:53 +0800
From:   Baoquan He <bhe@...hat.com>
To:     Dave Young <dyoung@...hat.com>
Cc:     kexec@...ts.infradead.org, linux-kernel@...r.kernel.org,
        keescook@...omium.org, ats-kumagai@...jp.nec.com,
        thgarnie@...gle.com, takahiro.akashi@...aro.org, mingo@...hat.com,
        ebiederm@...ssion.com, hpa@...or.com, tglx@...utronix.de,
        akpm@...ux-foundation.org, tonli@...hat.com, anderson@...hat.com,
        panand@...hat.com
Subject: Re: [PATCH] kexec: Export memory sections virtual addresses to
 vmcoreinfo

On 11/01/16 at 01:10pm, Dave Young wrote:
> On 10/06/16 at 04:46pm, Baoquan He wrote:
> > KASLR memory randomization can randomize the base of the physical memory
> > mapping (PAGE_OFFSET), vmalloc (VMALLOC_START) and vmemmap
> > (VMEMMAP_START). These need be exported to VMCOREINFO so that user space
> > utility, mainly makedumpfile can use them to identify the base of each
> > memory section. Here using VMCOREINFO_NUMBER we can reuse the existing
> > struct number_table in makedumpfile to import data easily.
> > 
> > Since they are related to x86_64 only, put them into
> > arch_crash_save_vmcoreinfo. And move the exportion of KERNEL_IMAGE_SIZE
> > together since it's also for x86_64 only.
> > 
> > Signed-off-by: Baoquan He <bhe@...hat.com>
> > ---
> >  arch/x86/kernel/machine_kexec_64.c | 4 ++++
> >  kernel/kexec_core.c                | 3 ---
> >  2 files changed, 4 insertions(+), 3 deletions(-)
> > 
> > diff --git a/arch/x86/kernel/machine_kexec_64.c b/arch/x86/kernel/machine_kexec_64.c
> > index 5a294e4..e150dd7 100644
> > --- a/arch/x86/kernel/machine_kexec_64.c
> > +++ b/arch/x86/kernel/machine_kexec_64.c
> > @@ -337,6 +337,10 @@ void arch_crash_save_vmcoreinfo(void)
> >  #endif
> >  	vmcoreinfo_append_str("KERNELOFFSET=%lx\n",
> >  			      kaslr_offset());
> > +	VMCOREINFO_NUMBER(KERNEL_IMAGE_SIZE);
> > +	VMCOREINFO_NUMBER(PAGE_OFFSET);
> > +	VMCOREINFO_NUMBER(VMALLOC_START);
> > +	VMCOREINFO_NUMBER(VMEMMAP_START);
> 
> Pratyush has posted makedumpfile patches below to avoid the VMCOREINFO:
> http://lists.infradead.org/pipermail/kexec/2016-October/017540.html
> 
> But we have this in mainline which also introduced the VMCOREINFO
> numbers, can you send a patch to revert them?

OK, will do.

However for find_vmemmap_x86_64() in makedumpfile, vmemmap_start is
still needed. I checked code, seems no better way to avoid. I am not
sure how many people are really using "-e" option to exclude unused
vmemmap pages.

Maybe just leave it as is, and fix it when people complain?

> commit 0549a3c02efb350776bc869685a361045efd3a29
> Author: Thomas Garnier <thgarnie@...gle.com>
> Date:   Tue Oct 11 13:55:08 2016 -0700
> 
>     kdump, vmcoreinfo: report memory sections virtual addresses
> [snip]]
> 
> >  }
> >  
> >  /* arch-dependent functionality related to kexec file-based syscall */
> > diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c
> > index 5616755..8ad3a29e 100644
> > --- a/kernel/kexec_core.c
> > +++ b/kernel/kexec_core.c
> > @@ -1467,9 +1467,6 @@ static int __init crash_save_vmcoreinfo_init(void)
> >  #endif
> >  	VMCOREINFO_NUMBER(PG_head_mask);
> >  	VMCOREINFO_NUMBER(PAGE_BUDDY_MAPCOUNT_VALUE);
> > -#ifdef CONFIG_X86
> > -	VMCOREINFO_NUMBER(KERNEL_IMAGE_SIZE);
> > -#endif
> 
> Moving KERNEL_IMAGE_SIZE to x86 should be a standalone patch.
> I remember Dave Anderson said he use it in crash utility, cced him.
> 
> >  #ifdef CONFIG_HUGETLB_PAGE
> >  	VMCOREINFO_NUMBER(HUGETLB_PAGE_DTOR);
> >  #endif
> > -- 
> > 2.5.5
> > 
> > 
> > _______________________________________________
> > kexec mailing list
> > kexec@...ts.infradead.org
> > http://lists.infradead.org/mailman/listinfo/kexec
> 
> Thanks
> Dave

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