linux-kernel - Re: How could we get rid of saved_max

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Date:	Wed, 5 Mar 2014 13:36:17 +0800
From:	WANG Chao <chaowang@...hat.com>
To:	Muli Ben-Yehuda <muli@...technion.ac.il>,
	"Jon D. Mason" <jdmason@...zu.us>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>, Vivek Goyal <vgoyal@...hat.com>,
	Yinghai Lu <yinghai@...nel.org>, Baoquan He <bhe@...hat.com>
Cc:	kexec@...ts.infradead.org, discuss@...-64.org, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: How could we get rid of saved_max_pfn for calgary iommu?

[ Add Muli, I find his new email in git log]

Hi, Muli

saved_max_pfn is becoming a setback for kexec-tools. Ideally calgary
could get rid of saved_max_pfn at all. But If this can't work, how about
exporting a calgary tce table size to user space, so that kexec-tools
can simply pass calgary=xxx cmdline to 2nd kernel.

What do you think of this problem?

BTW MAINTAINERS file still uses your old email, please update
accordingly.

Thanks
WANG Chao

On 02/19/14 at 02:18pm, WANG Chao wrote:
> Hi, All
> 
> arch/x86/kernel/pci-calgary.c is the only user of saved_max_pfn today:
> 
> int __init detect_calgary(void)
> {
> 	[..]
> 	specified_table_size = determine_tce_table_size((is_kdump_kernel() ?
> 					saved_max_pfn : max_pfn) * PAGE_SIZE);
> 	[..]
> }
> 
> saved_max_pfn is the real mem size and is calculated by 1st kernel E820
> memmap which is passed in by 2nd kernel's boot_params (done by kexec):
> 
> 	saved_max_pfn = e820_end_of_ram_pfn();
> 
> After saved_max_pfn has been set, memmap=exactmap will reset the E820
> provided by boot_params and use the user defined E820 instead.
> 
> Now we want to get rid of memmap=exactmap and directly pass the E820
> memmap by boot_params for some reason (eg. exactmap may exceed the cmdline
> size and also isn't compatible with kaslr).
> 
> However saved_max_pfn becomes the obstacle for obsoleting exactmap.
> Because it needs two conditions: first kernel's E820 map and
> memmap=exactmap cmdline.
> 
> So I'm wondering if it's possible to get rid of saved_max_pfn totally in
> calgary code. Or we can get saved_max_pfn using a different way, for
> example calculated in 1st kernel and passed in to 2nd kernel by cmdline.
> 
> Thanks
> WANG Chao
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