linux-kernel - Re: [PATCHv7] x86/kdump: bugfix, make the behavior of crashkernel=X consistent with kaslr

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Date:   Fri, 15 Feb 2019 11:24:58 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Dave Young <dyoung@...hat.com>
Cc:     bhe@...hat.com, Jerry Hoemann <jerry.hoemann@....com>,
        x86@...nel.org, Randy Dunlap <rdunlap@...radead.org>,
        kexec@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Pingfan Liu <kernelfans@...il.com>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        Andrew Morton <akpm@...ux-foundation.org>, yinghai@...nel.org,
        vgoyal@...hat.com
Subject: Re: [PATCHv7] x86/kdump: bugfix, make the behavior of crashkernel=X
 consistent with kaslr

On Tue, Feb 12, 2019 at 04:48:16AM +0800, Dave Young wrote:
> Even we make it automatic in kernel, but we have to have some default
> value for swiotlb in case crashkernel can not find a free region under 4G.
> So this default value can not work for every use cases, people need 
> manually use crashkernel=,low and crashkernel=,high in case
> crashkernel=X does not work.

Why would the user need to find swiotlb range? The kernel has all the
information it requires at its finger tips in order to decide properly.

The user wants a crashkernel range, the kernel tries the low range =>
no workie, then it tries the next range => workie but needs to allocate
swiotlb range so that DMA can happen too. Doh, then the kernel does
allocate that too.

Why would the user need to do anything here?!

-- 
Regards/Gruss,
    Boris.

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