On Wed, 2014-09-10 at 11:26 -0700, Andy Lutomirski wrote: > On Wed, Sep 10, 2014 at 9:51 AM, Toshi Kani <[email protected]> wrote: > > This patch changes reserve_memtype() to handle the WT cache mode. > > When PAT is not enabled, it continues to set UC- to *new_type for > > any non-WB request. > > > > When a target range is RAM, reserve_ram_pages_type() fails for WT > > for now. This function may not reserve a RAM range for WT since > > reserve_ram_pages_type() uses the page flags limited to three memory > > types, WB, WC and UC. > > Should it fail if WT is unavailable due to errata? More generally, > how are all of the do_something_wc / do_something_wt / > do_something_nocache helpers supposed to handle unsupported types?
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. The failure case above is a run-time error when WT is enabled and is targeted to RAM. In this case, reserve_memtype() fails and sets UC- to *new_type due to the limitation in page tables. set_memory_xzy() interfaces do not retry with new_type, but return an error. I think this makes sense since the caller should receive this error as this case is a bug in the code (while running it on an old system is not a bug). Thanks, -Toshi -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
