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Subject: Re: [PATCH 4/4] kdump: update Documentation about crashkernel on
 arm64
To:     Chen Zhou <chenzhou10@huawei.com>, catalin.marinas@arm.com,
        will.deacon@arm.com, akpm@linux-foundation.org,
        ard.biesheuvel@linaro.org, rppt@linux.ibm.com, tglx@linutronix.de,
        mingo@redhat.com, bp@alien8.de, ebiederm@xmission.com
Cc:     wangkefeng.wang@huawei.com, linux-mm@kvack.org,
        kexec@lists.infradead.org, linux-kernel@vger.kernel.org,
        takahiro.akashi@linaro.org, horms@verge.net.au,
        linux-arm-kernel@lists.infradead.org,
        "kexec@lists.infradead.org" <kexec@lists.infradead.org>,
        Bhupesh SHARMA <bhupesh.linux@gmail.com>
References: <20190507035058.63992-1-chenzhou10@huawei.com>
 <20190507035058.63992-5-chenzhou10@huawei.com>
From:   Bhupesh Sharma <bhsharma@redhat.com>
Message-ID: <de5b827f-5db2-2280-b848-c5c887b9bb58@redhat.com>
Date:   Wed, 15 May 2019 10:46:05 +0530
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On 05/07/2019 09:20 AM, Chen Zhou wrote:
> Now we support crashkernel=X,[high,low] on arm64, update the
> Documentation.
> 
> Signed-off-by: Chen Zhou <chenzhou10@huawei.com>
> ---
>   Documentation/admin-guide/kernel-parameters.txt | 6 +++---
>   1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index 268b10a..03a08aa 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -705,7 +705,7 @@
>   			memory region [offset, offset + size] for that kernel
>   			image. If '@offset' is omitted, then a suitable offset
>   			is selected automatically.
> -			[KNL, x86_64] select a region under 4G first, and
> +			[KNL, x86_64, arm64] select a region under 4G first, and
>   			fall back to reserve region above 4G when '@offset'
>   			hasn't been specified.
>   			See Documentation/kdump/kdump.txt for further details.
> @@ -718,14 +718,14 @@
>   			Documentation/kdump/kdump.txt for an example.
>   
>   	crashkernel=size[KMG],high
> -			[KNL, x86_64] range could be above 4G. Allow kernel
> +			[KNL, x86_64, arm64] range could be above 4G. Allow kernel
>   			to allocate physical memory region from top, so could
>   			be above 4G if system have more than 4G ram installed.
>   			Otherwise memory region will be allocated below 4G, if
>   			available.
>   			It will be ignored if crashkernel=X is specified.
>   	crashkernel=size[KMG],low
> -			[KNL, x86_64] range under 4G. When crashkernel=X,high
> +			[KNL, x86_64, arm64] range under 4G. When crashkernel=X,high
>   			is passed, kernel could allocate physical memory region
>   			above 4G, that cause second kernel crash on system
>   			that require some amount of low memory, e.g. swiotlb
> 

IMO, it is a good time to update 'Documentation/kdump/kdump.txt' with 
this patchset itself for both x86_64 and arm64, where we still specify 
only the old format for 'crashkernel' boot-argument:

Section: Boot into System Kernel
          =======================

On arm64, use "crashkernel=Y[@X]".  Note that the start address of
the kernel, X if explicitly specified, must be aligned to 2MiB (0x200000).
...

We can update this to add the new crashkernel=size[KMG],low or 
crashkernel=size[KMG],high format as well.

Thanks,
Bhupesh