Messages in this thread | | | Date | Wed, 11 Jun 2008 18:12:34 +0200 | From | Andreas Herrmann <> | Subject | Re: [PATCH 2/5] x86: PAT: fix ambiguous paranoia check in pat_init() |
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On Wed, Jun 11, 2008 at 02:58:49PM +0200, Rene Herman wrote: > On 11-06-08 11:41, Andreas Herrmann wrote: > >> As I had no Transmeta or Centaur CPU at hand I just cleared the PAT >> flag in the CPU identification code to simulate the case that all CPUs >> of a Vendor are whitelisted (even those w/o PAT support). The first >> time pat_init() is entered you get >> PAT enabled, but CPU feature cleared (=> which is wrong as no flag >> was cleared) > > Again, you are misreading this. Please just replace the message mentally by > "PAT enabled, but CPU claims to not support PAT". "cleared" here does not > signify that we ourselves cleared anything, just that flag IS clear > (unset). Yes, maybe the wording could be better but it's not wrong.
Well, wording might not be best. But I don't care anymore. (Just wondering which CPUs are out there that support PAT but don't advertise it with any feature flag.)
>> x86 PAT enabled: cpu 0, old 0x7040600070406, new 0x7010600070106 >> (=> which is wrong as PAT shouldn't be enabled on such CPUs) > > Again not wrong, or at least by design. Thomas Gleixner did it this way and > with that "paranoia check" explicitly bombing out only for SMP this > wouldn't have been by accident. He no doubt knows why he did so (and he's > in CC so if we're real lucky we might also now...)
I guess at the time Thomas' patch was commited this was just fine.
But with the recent Transmeta/Centaur patch, validate_pat_support() returns w/o disabling PAT even for such vendor's CPUs that don't support PAT,
To prevent this, validate_pat_support() should check for cpu_has_pat in addition to any other white-black-or-whatsoever-listing.
Regards,
Andreas
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