On Sun, Jul 31, 2016, at 19:07, Pascal Hambourg wrote: > Le 01/08/2016 à 00:00, Stephen Powell a écrit : >> one's processor supports PAE, but the motherboard only supports a maximum of >> 2 GiB of RAM, what does a PAE kernel buy one? Nothing, as far as I can see. > > PAE allows to use the NX/XD bit on CPU which support it to prevent > execution of data memory areas.
To the best of my knowledge, there are no 32-bit-only processors which support the NX bit. A 32-bit PAE-enabled kernel can only use NX if it is running on a 64-bit-capable processor. I should have explicitly stated what was an implicit assumption, namely, that the processor is not 64-bit capable. To give a specific example, my IBM ThinkPad X31 has a Pentium M processor, which is PAE capable and 32 bit only, and the motherboard only supports a maximum of 2 GiB of RAM. I *can* run a PAE-enabled kernel on it, but a PAE-enabled kernel uses more memory. PAE allows more than 4 GiB of memory to be accessed, but I don't have that much. And the PAE kernel can't exploit the NX bit, because the processor doesn't support it. A PAE-enabled kernel actually *hurts* me in this case. I'm better off running a non-PAE kernel, even though the processor supports PAE. -- .''`. Stephen Powell <zlinux...@fastmail.com> : :' : `. `'` `-
