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

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Date:   Tue, 1 Nov 2016 10:13:34 -0400 (EDT)
From:   Dave Anderson <anderson@...hat.com>
To:     Baoquan He <bhe@...hat.com>
Cc:     Dave Young <dyoung@...hat.com>, kexec@...ts.infradead.org,
        linux-kernel@...r.kernel.org, keescook@...omium.org,
        ats-kumagai@...jp.nec.com, thgarnie@...gle.com,
        takahiro akashi <takahiro.akashi@...aro.org>, mingo@...hat.com,
        ebiederm@...ssion.com, hpa@...or.com, tglx@...utronix.de,
        akpm@...ux-foundation.org, tonli@...hat.com, panand@...hat.com
Subject: Re: [PATCH] kexec: Export memory sections virtual addresses to
 vmcoreinfo

----- Original Message -----
> 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?

Speaking of complaints, is there any chance you can make the
x86_64 "phys_base" value available?  The VMCOREINFO_SYMBOL(phys_base)
is useless since its contents are needed in order to access the
symbol address.

Dave

> 
> > 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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