On Fri, Feb 06, 2009 at 11:50:26PM +0100, Stefan Reinauer wrote:
ron minnich wrote:
Stepan can tell us, since he has working smm on kontron, but I can not believe smm can not be cached.
Occasionally a CPU might do speculative readahead on the SMRAM memory while not in SMM. The chipset will generate master aborts on the PCI bus, so the cached data is incorrect (0xff) and upon SMM entry the CPU goes to nirvana. The SMM area in ASEG is always uncached. The upper SMRAM areas can be cached, but they must only be cached while in SMM.
If there is memory only accessible from SMM mode, then I agree it would need to be uncached. I thought that Jason was just reserving memory for use by SMM - memory that could also be read/written in non-SMM mode. In that case, I did not think caching needed to be disabled. Indeed, the intel system programming guide recommends using some cached memory for SMM.
-Kevin
Random thought - I wonder if the OS could "break into" SMM mode by turning on caching for the SMM area and then manipulating the cache contents so that an SMI used icache/dcache contents set by the OS.