On Wed, Sep 10, 2014 at 1:30 PM, Toshi Kani <toshi.kani@xxxxxx> wrote: > On Wed, 2014-09-10 at 13:14 -0700, H. Peter Anvin wrote: >> On 09/10/2014 12:30 PM, Toshi Kani wrote: >> > >> > When WT is unavailable due to the PAT errata, it does not fail but gets >> > redirected to UC-. Similarly, when PAT is disabled, WT gets redirected >> > to UC- as well. >> > >> >> But on pre-PAT hardware you can still do WT. > > Yes, if we manipulates the bits directly, but such code is no longer > allowed for PAT systems. The PAT-based kernel interfaces won't work for > pre-PAT systems, and therefore requests are redirected to UC- on such > systems. > Right, the PWT bit. Forgot about that. I wonder whether it would make sense to do some followup patches to replace the current support for non-PAT machines with a "PAT" and corresponding reverse map that exactly matches the mapping when PAT is disabled. These patches are almost there. --Andy -- 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>