On Mon, Aug 1, 2016, at 19:30, Pascal Hambourg wrote: > Le 01/08/2016 à 04:02, Stephen Powell a écrit : >> >> 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. > > You should check your information. A number of late 32-bit Pentium 4 and > Pentium M models support the NX bit. >
Perhaps there are some 32-bit-only processors which support XD/NX. But none of mine do. >> >> To give a specific example, my IBM ThinkPad X31 has >> a Pentium M processor, which is PAE capable and 32 bit only (...) >> And the PAE kernel >> can't exploit the NX bit, because the processor doesn't support it. > > This is really surprising because, according to > <https://en.wikipedia.org/wiki/Pentium_M>, Pentium M models which > support PAE also support the NX bit. Actually, PAE support was added > just to support the NX bit, the physical address size is still 32 bits. > You should check your information. :-) That same Wikipedia article that you quoted above also says this: "The Banias family processors internally support PAE but do not show the PAE support flag in their CPUID information ..." All Pentium M processors support PAE, they just don't all advertise such support in the output of the CPUID instruction. My IBM ThinkPad X31 has a Banias-class Pentium M processor. I can get a PAE-enabled kernel to run on it, but I must use the "forcepae" kernel boot parameter in order to get it to work. My original point remains. If one's computer has less than 4 GiB of memory installed, and the processor does not support the XD/NX bit, then running a 32-bit PAE-enabled kernel does not benefit one at all. In fact, it actually hurts one, because a PAE-enabled kernel uses more memory. Debian is one of the few distributions to still provide non-PAE kernels. And I applaud them for doing so for just such situations as I described above. Just because one's processor supports PAE doesn't necessarily mean that one benefits from using a PAE kernel. In addition to my IBM ThinkPad X31, I have two other 32-bit-only machines. One uses a Pentium 4 processor, the other uses a Xeon. None of them support the NX bit. And none of them have more than 4 GiB of memory installed. (Only the ThinkPad requires the "forcepae" kernel boot parameter to get a PAE-enabled kernel to run.) -- .''`. Stephen Powell <zlinux...@fastmail.com> : :' : `. `'` `-
