Re: [PATCH] x86: fix kaslr and memmap collision

From: Dave Chinner
Date: Wed Nov 23 2016 - 19:05:42 EST

On Tue, Nov 22, 2016 at 11:01:32AM -0800, Dan Williams wrote:
> On Tue, Nov 22, 2016 at 10:54 AM, Kees Cook <keescook@xxxxxxxxxxxx> wrote:
> > On Tue, Nov 22, 2016 at 9:26 AM, Dan Williams <dan.j.williams@xxxxxxxxx> wrote:
> >> No, you're right, we need to handle multiple ranges. Since the
> >> mem_avoid array is statically allocated perhaps we can handle up to 4
> >> memmap= entries, but past that point disable kaslr for that boot?
> >
> > Yeah, that seems fine to me. I assume it's rare to have 4?
> >
> It should be rare to have *one* since ACPI 6.0 added support for
> communicating persistent memory ranges. However there are legacy
> nvdimm users that I know are doing at least 2, but I have hard time
> imagining they would ever do more than 4.

I doubt it's rare amongst the people using RAM to emulate pmem for
filesystem testing purposes. My "pmem" test VM always has at least 2
ranges set to give me two discrete pmem devices, and I have used 4
from time to time to do things like test multi-volume scratch XFS
filesystems in xfstests (i.e. data, log and realtime volumes) so I
didn't need to play games with partitioning or DM...


Dave Chinner