On 09/14/2018 01:39 PM, Yu-cheng Yu wrote:

With the updated ptep_set_wrprotect() below, I did MADV_WILLNEED to a shadow
stack of 8 MB, then 10,000 fork()'s, but could not prove it is more or less
efficient than the other. A So can we say this is probably fine in terms of
efficiency?

Well, the first fork() will do all the hard work.  I don't think
subsequent fork()s will be affected.

Did you do something to ensure this code was being run?

I would guess that a loop like this:

	for (i = 0; i < 10000; i++) {
		mprotect(addr, len, PROT_READ);
		mprotect(addr, len, PROT_READ|PROT_WRITE);
	}

might show it better.