linux-kernel - Re: [PATCH 1/2 v6] x86/kexec_file: add e820 entry in case e820 type string matches to io resource name

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Message-ID: <20181114112600.GD13926@zn.tnic>
Date:   Wed, 14 Nov 2018 12:26:01 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Lianbo Jiang <lijiang@...hat.com>
Cc:     linux-kernel@...r.kernel.org, kexec@...ts.infradead.org,
        x86@...nel.org, tglx@...utronix.de, mingo@...hat.com,
        akpm@...ux-foundation.org, dyoung@...hat.com, bhe@...hat.com
Subject: Re: [PATCH 1/2 v6] x86/kexec_file: add e820 entry in case e820 type
 string matches to io resource name

On Wed, Nov 14, 2018 at 03:29:25PM +0800, Lianbo Jiang wrote:
> When load the kernel image and initramfs by kexec_file_load syscall, it can
> not add exact e820 reserved type to kdump kernel e820 table.
> 
> Kdump uses walk_iomem_res_desc() to iterate io resources, then adds matched
> desc to e820 table for kdump kernel. But, when convert the e820 type into
> the iores descriptors, several e820 types are converted to 'IORES_DES_NONE'
> in this function e820_type_to_iores_desc(). So the walk_iomem_res_desc()
> will get these unnecessary types(E820_TYPE_RAM/E820_TYPE_UNUSABLE/E820_TYPE
> _KERN) when iterate io resources by the 'IORES_DES_NONE'.
> 
> It needs filter out these redundant type(such as E820_TYPE_RAM/E820_TYPE_
> UNUSABLE/E820_TYPE_KERN) in order to add exact e820 reserved type to kdump
> kernel e820 table. Thus it also needs an extra checking in memmap_entry_
> callback() to match the e820 type and resource name.

Ok, it took me a while to parse what this is trying to say so let's
start from the top:

* What resource type do you do need in the second kernel?

* The most important question: why?

* If it is the reserved resource, why aren't you adding
IORES_DESC_RESERVED or so which to look for instead of this hacky string
comparison?

-- 
Regards/Gruss,
    Boris.

Good mailing practices for 400: avoid top-posting and trim the reply.