[coreboot] Cache as RAM - is it possible to execute code in cache?

Carl-Daniel Hailfinger c-d.hailfinger.devel.2006 at gmx.net
Fri Sep 5 11:44:20 CEST 2008

On 05.09.2008 09:46, ron minnich wrote:
> On Fri, Sep 5, 2008 at 12:45 AM, Jackie Pan <jackiepan93 at gmail.com> wrote:
>> I'm wondering if it's possible to place code into cache-emulated RAM, I
>> tested on an intel T2300,
>> after CAR setup, I can read/write to the mapped region, however code
>> execution seems not working.
>> Postcode reveals that the CPU seems to be spinning on the very first
>> instruction in the 'RAM' region.
>> Anyone could give some hints? thanks.
> It is possible and it works. What you might do is dump the contents of
> the CAR once you have copied to it and see what is there.

Yes and no. At least the new AMD Family 10h processors can't use CAR for
data storage and code storage at the same time. In theory, you could
fill the CAR area in data storage mode, then switch over to code
storage. Not tested, though, and NOT mentioned as viable in the BKDG
(BIOS and Kernel Developer's Guide).

Intel CPUs might have similar restrictions.



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