linux-kernel - Re: [PATCH v2 2/2] kexec: Consider crashk_low_res in sanity_check_segment

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Date:	Wed, 17 Aug 2016 15:24:20 +0800
From:	Dave Young <dyoung@...hat.com>
To:	Xunlei Pang <xlpang@...hat.com>
Cc:	linux-kernel@...r.kernel.org, kexec@...ts.infradead.org,
	akpm@...ux-foundation.org, ebiederm@...ssion.com,
	Vivek Goyal <vgoyal@...hat.com>, Baoquan He <bhe@...hat.com>
Subject: Re: [PATCH v2 2/2] kexec: Consider crashk_low_res in
 sanity_check_segment_list()

Hi, Xunlei,

On 08/17/16 at 09:50am, Xunlei Pang wrote:
> We have crashk_res only in most cases, but sometimes we have
> crashk_low_res.
> 
> For example, on 64-bit x86 systems, when "crashkernel=32M,high"
> combined with "crashkernel=128M,low" is used, so some segments
> may have the chance to be loaded into crashk_low_res area. We
> can't fail it as a memory violation in these cases.
> 
> Thus, we add the case to regard the segment as valid if it is
> within crashk_low_res.

crashkernel low is meant for swiotlb, it can be reserved automaticlly
in case there's only crashkernel high specified in cmdline, I'm not
sure it is useful to use crashk_res_low for other purpose and
likely kdump can fail in the case. 

I'm not sure it is really necessary to add this check now, we may
handle it only when there is an actual use case and bug report in
the future.

Thanks
Dave
> 
> Signed-off-by: Xunlei Pang <xlpang@...hat.com>
> ---
>  kernel/kexec_core.c | 11 ++++++++---
>  1 file changed, 8 insertions(+), 3 deletions(-)
> 
> diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c
> index 707d18e..9012a60 100644
> --- a/kernel/kexec_core.c
> +++ b/kernel/kexec_core.c
> @@ -248,9 +248,14 @@ int sanity_check_segment_list(struct kimage *image)
>  			mstart = image->segment[i].mem;
>  			mend = mstart + image->segment[i].memsz - 1;
>  			/* Ensure we are within the crash kernel limits */
> -			if ((mstart < phys_to_boot_phys(crashk_res.start)) ||
> -			    (mend > phys_to_boot_phys(crashk_res.end)))
> -				return -EADDRNOTAVAIL;
> +			if ((mstart >= phys_to_boot_phys(crashk_res.start)) &&
> +			    (mend <= phys_to_boot_phys(crashk_res.end)))
> +				continue;
> +			if ((mstart >= phys_to_boot_phys(crashk_low_res.start)) &&
> +			    (mend <= phys_to_boot_phys(crashk_low_res.end)))
> +				continue;
> +
> +			return -EADDRNOTAVAIL;
>  		}
>  	}
>  
> -- 
> 1.8.3.1
>