Re: [Patch] Per CPU MCA/INIT data save areas

On Tue, 14 Sep 2004 10:30:44 -0500 (CDT), 
Russ Anderson <rja@sgi.com> wrote:
>Thanks for the response.  Some comments below...
>Takao Indoh wrote:
>> BTW, I used tpa to get physical address, but I am not sure TLB is valid 
>> in the OS_INIT. tpa is available?
>
>There may not be a valid TLB.  That's why DATA_VA_TO_PA() cannot be used
>in the OS_MCA path.  LOAD_PHYSICAL() is used instead (in the original MCA code).  
>I'm not sure if LOAD_PHYSICAL() is sufficient either in this context (but that 
>may just be my lack of understanding).

LOAD_PHYSICAL() only works for physically unique addresses (one to one
mapping from virtual to physical address at load time), it does not
work for replicated areas like the per cpu data area.  As Russ has
said, tpa is not reliable in MCA/INIT paths, one of the possible
reasons for taking an MCA is an invalid tlb load :(.  Which means that
we need a second data area which contains the physical addresses of
each of the per cpu data areas.  MCA/INIT can do a LOAD_PHYSICAL() on
the start of that table, then index by cpu to get the physical address
of the local per cpu table.

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