On Wed, Apr 30, 2014 at 6:19 AM, Nikolay Borisov
[off-list ref] wrote:

quoted

From: Will Deacon [mailto:will.deacon at arm.com]
Hi Nikolay,

On Mon, Apr 28, 2014 at 10:31:44AM +0100, Nikolay Borisov wrote:

quoted

This patch makes kexec work on a kernel that has its .text section

set to read

quoted

only. The main reason of doing it is because there is a patch in the

making

quoted

(http://lists.infradead.org/pipermail/linux-arm-kernel/2014-

April/244779.html)

quoted

which aims to make it possible to flag the kernel's code section as

read-only,

quoted

rendering kexec inoperable.

The first patch does the actual functional changes while the 2nd one

is

quoted

optional and is only to be used in case you have already applied the

aforementioned

quoted

CONFIG_DEBUG_RODATA patch

Patch 3 is also optional and tries to make the assembly code a bit

more "sane"

quoted

by introducing a .struct to describe the parameters for the kernel

relocation

quoted

stub.

Those patches have been tested on linux 3.14 on THUMB-2/non-THUMB-2

host

quoted

kernels.

Patch 1 and 3 apply cleanly on 3.15-rc3 and Patch 2 applies cleanly,

provided

quoted

that Kees' patch is applied as well.

Kees also managed to test that on a QEMU 2.0 based machine.

Wouldn't it be far simpler to set_kernel_text_rw() on a kexec? At this
point, we've committed to replacing our image, so whether we can write
to the .text of the old image before we clobber it entirely seems somewhat
moot to me.

We are poking one of the values in the prepare stage so doing set_kernel_text_rw() there
won't be very clean solution. However, I agree that if the values being poked into the prep

set_kernel_text_rw() is also mm-specific, since the PMD sections are
copied per-mm. I'm not sure if that's as much of a problem here since
the prepare looks to be all in the same thread, but if we can avoid
set_kernel_text_rw() that'll probably make things less surprising if
changes are made later on.

-Kees

stage is stashed in a static variable and then in the kexec_execute function we make the kernel
RW since we are turning the MMO off and nuking the old kernel anyway.

quoted

Will

Regards,
Nikolay

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