[lkml]   [2018]   [Aug]   [30]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: [PATCH 0/3] Add restrictions for kexec/kdump jumping between 5-level and 4-level kernel
On Wed, Aug 29, 2018 at 10:16:21PM +0800, Baoquan He wrote:
> This was suggested by Kirill several months ago, I worked out several
> patches to fix, then interrupted by other issues. So sort them out
> now and post for reviewing.

Thanks for doing this.

> The current upstream kernel supports 5-level paging mode and supports
> dynamically choosing paging mode during bootup according to kernel
> image, hardware and kernel parameter setting. This flexibility brings
> several issues for kexec/kdump:
> 1)
> Switching between paging modes, requires changes into target kernel.
> It means you cannot kexec() 4-level paging kernel from 5-level paging
> kernel if 4-level paging kernel doesn't include changes.
> 2)
> Switching from 5-level paging to 4-level paging kernel would fail, if
> kexec() put kernel image above 64TiB of memory.

I'm not entirely sure that 64TiB is the limit here. Technically, 4-level
paging allows to address 256TiB in 1-to-1 mapping. We just don't have
machines with that wide physical address space (which don't support
5-level paging too).

What is your reasoning about 64TiB limit?

Kirill A. Shutemov

 \ /
  Last update: 2018-08-30 16:00    [W:0.096 / U:2.976 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site