On Thu, Aug 13, 2015 at 5:48 AM, Adrian Danis <adrian.danis@nicta.com.au> wrote:

Currently there is no support in seL4 for taking advantage of hardware support for detecting dirty/accessed pages. If you want this then you must emulate this in software by changing the access writes on pages and handling the resulting page faults.

The reason for not supporting any underlying hardware features for this is the original, and verified, platform that seL4 was written, an armv6, did not have hardware support for tracking this.

Since porting seL4 to x86 and newer ARM architectures that have support for this there has not been any perceived need for this, so it has not been done. There is certainly no reason requesting such information could not be done within the capability model.

This is why I was asking if having mapping rights on the page descriptor/page table would be sufficient.  If you can change which physical page a virtual address refers to, you could probably also have enough privilege to be trusted with dirty/accessed bit.

Is this the sort of "within the capability model" you are referring to?