Re: [patch v2 02/10] kdump: Make kimage_load_crash_segment() weak

Vivek Goyal
2011-08-01T20:31:43Z

On Wed, Jul 27, 2011 at 02:55:06PM +0200, Michael Holzheu wrote:
> From: Michael Holzheu <holzheu@linux.vnet.ibm.com>
>
> On s390 we do not create page tables at all for the crashkernel memory.
> This requires a s390 specific version for kimage_load_crash_segment().
> Therefore this patch declares this function as "__weak". The s390 version is
> very simple. It just copies the kexec segment to real memory without using
> page tables:
>
> int kimage_load_crash_segment(struct kimage *image,
> struct kexec_segment *segment)
> {
> return copy_from_user_real((void *) segment->mem, segment->buf,
> segment->bufsz);
> }
>
> There are two main advantages of not creating page tables for the
> crashkernel memory:
>
> a) It saves memory. We have scenarios in mind, where crashkernel
> memory can be very large and saving page table space is important.
> b) We protect the crashkernel memory from being overwritten.
>
> Signed-off-by: Michael Holzheu <holzheu@linux.vnet.ibm.com>
> ---
> kernel/kexec.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> --- a/kernel/kexec.c
> +++ b/kernel/kexec.c
> @@ -842,8 +842,8 @@ out:
> return result;
> }
>
> -static int kimage_load_crash_segment(struct kimage *image,
> - struct kexec_segment *segment)
> +int __weak kimage_load_crash_segment(struct kimage *image,
> + struct kexec_segment *segment)

A comment here why we are making it weak should help in increasing
the code readability.

Thanks
Vivek

> {
> /* For crash dumps kernels we simply copy the data from
> * user space to it's destination.