On Thu, Sep 4, 2014 at 5:29 PM, Toshi Kani <toshi.kani@xxxxxx> wrote: > On Thu, 2014-09-04 at 16:34 -0700, Andy Lutomirski wrote: >> On Thu, Sep 4, 2014 at 4:19 PM, Henrique de Moraes Holschuh >> <hmh@xxxxxxxxxx> wrote: >> > On Thu, 04 Sep 2014, H. Peter Anvin wrote: >> >> On 09/04/2014 01:11 PM, Henrique de Moraes Holschuh wrote: >> >> > I am worried of uncharted territory, here. I'd actually advocate for not >> >> > enabling the upper four PAT entries on IA-32 at all, unless Windows 9X / XP >> >> > is using them as well. Is this a real concern, or am I being overly >> >> > cautious? >> >> >> >> It is extremely unlikely that we'd have PAT issues in 32-bit mode and >> >> not in 64-bit mode on the same CPU. >> > >> > Sure, but is it really a good idea to enable this on the *old* non-64-bit >> > capable processors (note: I don't mean x86-64 processors operating in 32-bit >> > mode) ? >> > >> >> As far as I know, the current blacklist rule is very conservative due to >> >> lack of testing more than anything else. >> > >> > I was told that much in 2009 when I asked why cpuid 0x6d8 was blacklisted >> > from using PAT :-) >> >> At the very least, anyone who plugs an NV-DIMM into a 32-bit machine >> is nuts, and not just because I'd be somewhat amazed if it even >> physically fits into the slot. :) > > According to the spec, the upper four entries bug was fixed in Pentium 4 > model 0x1. So, the remaining Intel 32-bit processors that may enable > the upper four entries are Pentium 4 model 0x1-4. Should we disable it > for all Pentium 4 models? Assuming that this is Pentium 4 erratum N46, then there may be another option: use slot 7 instead of slot 4 for WT. Then, even if somehow the blacklist screws up, the worst that happens is that a WT page gets interpreted as UC. I suppose this could cause aliasing issues, but can't cause problems for people who don't use the high entries in the first place. --Andy > > Thanks, > -Toshi > -- Andy Lutomirski AMA Capital Management, LLC -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>