[coreboot] 0xE0000/0xF0000 segment issue

Naresh G. Solanki naresh.solanki.2011 at gmail.com
Thu Mar 19 15:38:58 CET 2015

Hi All,

I'm trying to port coreboot with seabios payload.
Everything goes fine till the control is transferred to payload.

Since payload is loaded between memory range 0xC_0000 - 0x10_0000.

The problem I was facing was that the board was going to auto reboot mode
while executing payload..

Once it reboot then I'm not able  to control the processor through XDP
until I manually do CPU reset.

It keeps on rebooting once control is transferred to payload.

To find out the cause I did detailed memory test & found out that the
memory range 0xA0000 - 0xBFFFF & 0xE0000 - 0xFFFFF always reads 0xFF.

since payload is loaded in the same region so before jmp_payload, I tried
to read this region through XDP & found payload code exist.

so I introduced wbinvd instruction just before jmp_payload & I found that
the  XDP started reading 0xFF in the memory range  0xE0000 - 0xFFFFF.

Thus from this I conclude that before the payload was able to execute
because of cached copy of it in CPU cache & it didn't really existed in RAM.

Also to enable  memory range 0xE_0000 to 0xF_FFFF  I have followed the
guidlines  as per table 15 of the document

Is that OK.
What I can do to successfully enable the memory range  0xE_0000 to 0xF_FFFF
for read write operation so that my payload execution goes undisturbed.

My ultimate aim is to load Windows by Seabios as payload.

N Solanki
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