Re: Question regarding the kexec support for FSL Book E

From: Suzuki Poulose <suzuki@in.ibm.com>
To: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: McClintock Matthew-B29882 <B29882@freescale.com>,
	"kexec@lists.infradead.org" <kexec@lists.infradead.org>,
	Ananth N Mavinakayanahalli <ananth@in.ibm.com>
Subject: Re: Question regarding the kexec support for FSL Book E
Date: Fri, 08 Apr 2011 10:17:17 +0530	[thread overview]
Message-ID: <4D9E9355.8010407@in.ibm.com> (raw)
In-Reply-To: <20110407162258.GA15298@linutronix.de>

On 04/07/11 21:52, Sebastian Andrzej Siewior wrote:
> * McClintock Matthew-B29882 | 2011-04-07 15:19:12 [+0000]:
>
>> On Thu, Apr 7, 2011 at 6:08 AM, Suzuki Poulose<suzuki@in.ibm.com>  wrote:
>>> How is this case taken care of ? Is it via the temporary mapping ? What is
>>> the virtual
>>>   address used by temporary mapping for the "relocate_new_kernel()" ?
>
> It is the same as the physical :) It is hard to tell where exactly the
> kernel image will be. It is somewhere between 0 and
> KEXEC_CONTROL_MEMORY_LIMIT. It is allocated in
> kimage_alloc_normal_control_pages(). It should not matter where it is.

I guess I got my answer :). The virtual address of the relocate_new_kernel() is
a kernel space VA, and hence would be above 2G (> PAGE_OFFSET), so there won't
be a clash of the 1:1 mapping that we create. Also, the src/destination pages
won't overlap the with the relocate_new_kernel. Hence we are safe.

>
>> When you load the new kexec image with kexec -l, I believe we make
>> sure we are in the first 2gb of memory. Then when you kexec, all the
>> TLB's are torn down and we setup a 1:1 virtual:physical mapping for
>> the first 2GB of memory. Then some assembly copies kernel from the
>> stored location to the destination and we boot the new kernel.
>
> arch/powerpc/include/asm/kexec.h:
> |#ifdef CONFIG_FSL_BOOKE
> |
> |/*
> | * On FSL-BookE we setup a 1:1 mapping which covers the first 2GiB of memory
> | * and therefore we can only deal with memory within this range
> | */
> |#define KEXEC_SOURCE_MEMORY_LIMIT      (2 * 1024 * 1024 * 1024UL - 1)
> |#define KEXEC_DESTINATION_MEMORY_LIMIT (2 * 1024 * 1024 * 1024UL - 1)
> |#define KEXEC_CONTROL_MEMORY_LIMIT     (2 * 1024 * 1024 * 1024UL - 1)
> |
> |#else
>
> So the kernel never gives memory above 2GiB to userland.
Right. If the page allocated is above 2GiB Physical Address, it is discarded,
and we look for new page.

Thanks

Suzuki

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