[coreboot] cached SMI handler

Carl-Daniel Hailfinger c-d.hailfinger.devel.2006 at gmx.net
Sat Feb 7 01:45:55 CET 2009

On 07.02.2009 01:39, Kevin O'Connor wrote:
> 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.

AFAICS it should work. CAR would be ideal for that purpose. No idea what
happens if the SMM code plays with the cache regs as well, though.



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