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

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Date:   Wed, 2 Nov 2016 21:48:25 +0800
From:   Baoquan He <bhe@...hat.com>
To:     Dave Anderson <anderson@...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

On 11/02/16 at 09:29am, Dave Anderson wrote:
> 
> 
> ----- Original Message -----
> > Hi Dave,
> > 
> > On 11/01/16 at 10:13am, Dave Anderson wrote:
> > > 
> > > 
> > > > > 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.
> > 
> > Yeah, the current exporting of virt addr of phys_base is really useless
> > for x86_64. While I saw you have got phys_base from kdump-ed vmcore elf
> > program header since kexec-tools has created that pt_load for kernel text
> > region.
> > 
> > machdep->machspec->phys_base = phdr->p_paddr - (phdr->p_vaddr &
> > ~(__START_KERNEL_map));
> > 
> > Do you still want the value of phys_base? If yes, I can change it to
> > export the real value of phys_base, not &phys_base.
> > 
> > In fact, exporting &phys_base was done in 2008, makedumpfile has taken
> > the similar way you use in crash to get value of phys_base. Means it has
> > been ignored very earlier. You could be the first person to complain
> > about it.
> 
> No, this is not the first time it's been brought up.  Anyway, yes,
> it would be preferable if it were readily available in vmcoreinfo
> rather than depending upon the PT_LOAD semantics. 

All right, I need move KERNEL_IMAGE_SIZE to x86 64. Can change it in the
same patch. Will CC you when post.

Thanks
Baoquan