linux-kernel - Re: [PATCH] x86/kexec: Exclude GART aperture from vmcore

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Date:   Tue, 7 Nov 2017 19:39:56 +0800
From:   Baoquan He <bhe@...hat.com>
To:     Jiri Bohac <jbohac@...e.cz>
Cc:     David Airlie <airlied@...ux.ie>, Dave Young <dyoung@...hat.com>,
        Vivek Goyal <vgoyal@...hat.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Toshi Kani <toshi.kani@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org,
        kexec@...ts.infradead.org, Borislav Petkov <bp@...en8.de>
Subject: Re: [PATCH] x86/kexec: Exclude GART aperture from vmcore

On 11/06/17 at 10:56am, Jiri Bohac wrote:
> On Mon, Nov 06, 2017 at 05:27:29PM +0800, Baoquan He wrote:
> > > 	00100000-c7e7ffff : System RAM
> > > 	  0b000000-0b792eb5 : Kernel code
> > > 	  0b792eb6-0bd5d47f : Kernel data
> > > 	  0c274000-0c3c8fff : Kernel bss
> > > 	  b7000000-c6ffffff : Crash kernel
> > 
> > It's weird, gart aperture located in crashkernel region? 
> 
> Ooops! I sent you a /proc/iomem from a different boot than the
> dmesg, whith different crashkernel= commandline. Sorry, this is
> the correct /proc/iomem:
> 
> 
> 	00000000-00000fff : Reserved
> 	00001000-0009d7ff : System RAM
> 	0009d800-0009ffff : Reserved
> 	000a0000-000bffff : PCI Bus 0000:00
> 	000c0000-000cafff : PCI Bus 0000:00
> 	  000c0000-000cafff : Video ROM
> 	000cb000-000ccfff : Adapter ROM
> 	000ce000-000fffff : Reserved
> 	  000f0000-000fffff : System ROM
> 	00100000-c7e7ffff : System RAM

AGP: Mapping aperture over RAM [mem 0xb8000000-0xbbffffff] (65536KB)

So on this system, gart is located inside 00100000-c7e7ffff : System
RAM.

I saw you defined the variable as xx_stolen_xx, does it mean that the
memory region where aperture located will be stolen from memory domain?
I am wondering if it will cause error when access this region from direct
mapping since allocate_aperture() is called in pci_iommu_alloc(), while
in setup_arch() we have built the direct mapping for all system
ram. Did I miss anything?

Anyway, if it should be excluded from crash memory region, can we dig it
away from /proc/iomem so that it's a hole in /proc/vmcore? Like this, we
don't worry about the user space kexec utility either. Could be I still
don't get it, may need to read the code of gart.

Thanks
Baoquan
> 	  c3000000-c77fffff : Crash kernel
> 	c7e80000-c7e8afff : ACPI Tables
> 	c7e8b000-c7e8cfff : ACPI Non-volatile Storage
> 	c7e8d000-c7ffffff : Reserved
> 	c8000000-ce0fffff : PCI Bus 0000:00
> 	  c8000000-c80003ff : IOAPIC 1
> 	  c8014000-c80143ff : 0000:00:11.0
> 	    c8014000-c80143ff : ahci
> 	  c8014400-c80144ff : 0000:00:12.2
> 	    c8014400-c80144ff : ehci_hcd
> 	  c8014800-c80148ff : 0000:00:13.2
> 	    c8014800-c80148ff : ehci_hcd
> 	  c8015000-c8015fff : 0000:00:12.0
> 	    c8015000-c8015fff : ohci_hcd
> 	  c8016000-c8016fff : 0000:00:12.1
> 	    c8016000-c8016fff : ohci_hcd
> 	  c8017000-c8017fff : 0000:00:13.0
> 	    c8017000-c8017fff : ohci_hcd
> 	  c8018000-c8018fff : 0000:00:13.1
> 	    c8018000-c8018fff : ohci_hcd
> 	  c8019000-c8019fff : 0000:00:14.5
> 	    c8019000-c8019fff : ohci_hcd
> 	  ca000000-cdffffff : PCI Bus 0000:01
> 	    ca000000-cbffffff : 0000:01:00.0
> 	      ca000000-cbffffff : bnx2
> 	    cc000000-cdffffff : 0000:01:00.1
> 	      cc000000-cdffffff : bnx2
> 	  ce000000-ce0fffff : PCI Bus 0000:02
> 	    ce000000-ce00ffff : 0000:02:06.0
> 	d0000000-d7ffffff : PCI Bus 0000:00
> 	  d0000000-d7ffffff : PCI Bus 0000:02
> 	    d0000000-d7ffffff : 0000:02:06.0
> 	e0000000-efffffff : Reserved
> 	  e0000000-efffffff : pnp 00:00
> 	    e0000000-e02fffff : PCI MMCONFIG 0000 [bus 00-02]
> 	fec00000-fec0ffff : Reserved
> 	  fec00000-fec003ff : IOAPIC 0
> 	fec10000-fec1001f : pnp 00:05
> 	fed00000-fed003ff : HPET 2
> 	  fed00000-fed003ff : PNP0103:00
> 	fed40000-fed45000 : PCI Bus 0000:00
> 	fee00000-fee00fff : Local APIC
> 	  fee00000-fee00fff : Reserved
> 	    fee00000-fee00fff : pnp 00:00
> 	fff00000-ffffffff : Reserved
> 	  fff00000-ffffffff : pnp 00:05
> 	100000000-837ffffff : System RAM
> 	  4df000000-4df792eb5 : Kernel code
> 	  4df792eb6-4dfd5d47f : Kernel data
> 	  4e0274000-4e03c8fff : Kernel bss
> 	  831000000-8374fffff : Crash kernel
> 
> Sorry for the confusion!
> 
> -- 
> Jiri Bohac <jbohac@...e.cz>
> SUSE Labs, Prague, Czechia
>