Hello Vivek,
On Thu, 2011-08-18 at 13:15 -0400, Vivek Goyal wrote:
> On Fri, Aug 12, 2011 at 03:48:51PM +0200, Michael Holzheu wrote:
> > From: Michael Holzheu <holzheu at 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.
>
> Michael,
>
> Thinking more about it. Can't we provide a arch specific version of
> kmap() and kunmap() so that we create temporary mappings to copy
> the pages and then these are torn off.
Isn't kmap/kunmap() used for higmem? These functions are called from
many different functions in the Linux kernel, not only for kdump. I
would assume that creating and removing mappings with these functions is
not what a caller would expect and probably would break the Linux kernel
at many other places, no?
Perhaps we can finish this discussion after my vacation. I will change
my patch series that we even do not need this patch...
So only two common code patches are remaining. I will send the common
code patches again and will ask Andrew Morton to integrate them in the
next merge window. The s390 patches will be integrated by Martin.
Michael
