linux-kernel - Re: [PATCH] x86/boot/KASLR: skip the specified crashkernel reserved region

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Message-ID: <20190225130452.GN14858@MiWiFi-R3L-srv>
Date:   Mon, 25 Feb 2019 21:05:04 +0800
From:   Baoquan He <bhe@...hat.com>
To:     Borislav Petkov <bp@...en8.de>, dyoung@...hat.com
Cc:     Pingfan Liu <kernelfans@...il.com>, x86@...nel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Will Deacon <will.deacon@....com>,
        Nicolas Pitre <nico@...aro.org>,
        Chao Fan <fanc.fnst@...fujitsu.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86/boot/KASLR: skip the specified crashkernel reserved
 region

On 02/25/19 at 10:45am, Borislav Petkov wrote:
> On Mon, Feb 25, 2019 at 03:59:56PM +0800, Pingfan Liu wrote:
> > crashkernel=x@y option may fail to reserve the required memory region if
> > KASLR puts kernel into the region. To avoid this uncertainty, making KASLR
> > skip the required region.
> 
> Lemme see if I understand this correctly: supplying crashkernel=X@Y
> influences where KASLR would put the randomized kernel. And it should be
> the other way around, IMHO. crashkernel= will have to "work" with KASLR
> to find a suitable range and if the reservation at Y fails, then we tell
> the user to try the more relaxed variant crashkernel=M.

Hmm, asking user to try crashkernel=M is an option. Users may want to
specify a region for crashkernel reservation, Just I forget in what case
they want crashkernel=x@y set. In crashkernel=x@y specified case, we may
truly need to avoid the already specified region.

Not sure if Dave still remember it. If no need, removing it is also
good.

Thanks
Baoquan