linux-kernel - Re: [PATCH V3 RFC 00/16] EFI stub for ARM

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Message-ID: <CAFECyb93p3Wct9DWYAzhU2cU1J=F6sN=67Vw3ofXFa8wW0EKrw@mail.gmail.com>
Date:	Mon, 12 Aug 2013 18:13:09 -0700
From:	Roy Franz <roy.franz@...aro.org>
To:	Mark Salter <msalter@...hat.com>
Cc:	linux-kernel@...r.kernel.org, linux-efi@...r.kernel.org,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>, matt.fleming@...el.com,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	Leif Lindholm <leif.lindholm@...aro.org>,
	Dave Martin <dave.martin@....com>
Subject: Re: [PATCH V3 RFC 00/16] EFI stub for ARM

On Mon, Aug 12, 2013 at 7:02 AM, Mark Salter <msalter@...hat.com> wrote:
> On Fri, 2013-08-09 at 16:26 -0700, Roy Franz wrote:
>> * Change FDT memory allocation to retry with a larger allocation if
>>   first educated guess is inadequate.
>
> With this change, it looks like you no longer free the original cmdline
> and fdt memory. The current flow looks like:
>
>   retry:
>      allocate_memory_for_expanded_fdt
>      get_memory_map
>      if (update_fdt() fails) {
>         free new_fdt and memory_map
>         goto retry
>      }
>
> So, this keeps the original fdt around and uses it as a starting point
> for newly allocated expanded fdt. You don't know if the new fdt is big
> enough until update_fdt() succeeds. But at that point, you already wrote
> the efi-runtime-mmap property with the memory_map still having the
> original cmdline and fdt in it.
>
> I think you should be able to have an expand_fdt() function which bumps
> the fdt size and uses the current fdt as the starting point instead of
> the original fdt. That way you can free the original fdt on the first
> iteration and free the original cmdline as soon as it is successfully
> written. Then the last thing you do if get the memory_map and write it.
>
> --Mark

Hi Mark,

I think this will work with the current FDT fields that are being set
by the stub.  In earlier
versions, I was also updating the reserved memory map using
fdt_add_mem_rsv(), so
iteratively updating the device tree wouldn't work. The reserved
regions would change,
and so the repeated updates would cause there to be repeated and
incorrect reserved regions.
I'm inclined to leave it as is, which should correctly update the
device tree even if methods like
fdt_add_mem_rsv() are used, with the tradeoff being there will be a
few more memory regions
for the kernel to free when it processes the EFI memory map.  The
kernel already needs to process
the EFI memory map to free the buffers use to load the kernel and
initrd, so these buffers will get freed, just not
by the stub.

Roy
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