On Thu, Jan 17, 2013 at 09:32:26PM +0000, John Baldwin wrote: > Author: jhb > Date: Thu Jan 17 21:32:25 2013 > New Revision: 245577 > URL: http://svnweb.freebsd.org/changeset/base/245577 > > Log: > Don't attempt to use clflush on the local APIC register window. Various > CPUs exhibit bad behavior if this is done (Intel Errata AAJ3, hangs on > Pentium-M, and trashing of the local APIC registers on a VIA C7). The > local APIC is implicitly mapped UC already via MTRRs, so the clflush isn't > necessary anyway. > > MFC after: 2 weeks I am curious, was there a case where the clflush was really executed on the LAPIC register window with the pristine HEAD code ? I think that there is no Intel processors which support clflush instruction and do not have self-snoop.
On the other hand, please note that the same change could be due for the pmap_invalidate_cache_pages(). Unlike pmap_invalidate_cache_range(), _pages() uses clflush unconditionally on purpose, since it is intended for devices which do not snoop.
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