Re: Regression: Requiring CAP_SYS_ADMIN for /proc/<pid>/pagemap causes application-level breakage

[Mark Seaborn]

On 24 April 2015 at 08:01, Mark Williamson
<mwilliamson@xxxxxxxxxxxxxxxxx> wrote:
> In our use of /proc/PID/pagemap, we currently make use of the physical
> pageframe addresses.  We should be able to work with a scrambled
> representation of these (Andy Lutomirski suggested this in the
> original discussion - https://lkml.org/lkml/2015/3/16/1273) so long as
> the scrambling remained consistent during the lifetime of the open
> pagemap file.  Alternatively, if physical addresses were simply zeroed
> (also suggested by Pavel Emelyanov -
> https://lkml.org/lkml/2015/3/9/871) we would be able to change our
> code to rely only on the soft-dirty flag and thus still work
> correctly.

I'm curious, what do you use the physical page addresses for?

Since you pointed to http://undo-software.com, which talks about
reversible debugging tools, I can guess you would use the soft-dirty
flag to implement copy-on-write snapshotting.  I'm guessing you might
use physical page addresses for determining when the same page is
mapped twice (in the same process or different processes)?

Cheers,
Mark
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/