[PATCH V4] powerpc/85xx: Add machine check handler to fix PCIe erratum on mpc85xx

[Scott Wood]

On 04/02/2013 04:28:10 AM, Jia Hongtao-B38951 wrote:
> 
> 
> > -----Original Message-----
> > From: Wood Scott-B07421
> > Sent: Saturday, March 30, 2013 12:34 AM
> > To: Jia Hongtao-B38951
> > Cc: Wood Scott-B07421; David Laight; linuxppc-dev at lists.ozlabs.org;
> > Stuart Yoder
> > Subject: Re: [PATCH V4] powerpc/85xx: Add machine check handler to  
> fix
> > PCIe erratum on mpc85xx
> >
> > On 03/29/2013 03:03:51 AM, Jia Hongtao-B38951 wrote:
> > > BTW, I'm still not sure how to deal with LD instruction with  
> update.
> >
> > You would need to do the update yourself.  Or just say that's a  
> case you
> > don't handle, and return 0.
> >
> > Again, please check for the size of the load operation.
> >
> > -Scott
> 
> For informing error to the process that hold the stall instruction
> we need to do:
> 1. Verify the instruction is load.
> 2. Fill the rd register with ~0UL.
> 3. Deal with the load instruction with update.
> 
> Here is the problems:
> 1. So many load instructions to handle. There are dozens of load  
> instructions
>    and most of them with different op code. Like:

If you don't want to handle all of them, then don't, but in case you  
run into an instruction you don't handle, don't skip it -- just let the  
normal machine check handler run.

> 
>    lbz: 1 0 0 0 1 0
>    lhz: 1 0 1 0 0 0
>    lwz: 1 0 0 0 0 0
>    ld : 1 1 1 0 1 0
>    ...
> 
>    Is there any available API for verifying the load instruction?

I don't know of anything in terms of an *API*... after all, you're not  
just "verifying" it, you're extracting information to determine how to  
emulate the instruction.

As for code you could borrow from, there's KVM emulation and probably  
other places.

> 2. For different size of load operation could we just fill the rd  
> register with
>    ~0UL?

Who knows in what ways the compiler is making assumptions about the  
upper bits being zero after an lbz, etc...

> 3. A load instruction with update could not just verified by op code.  
> I'd like
>    to leave it along. I think we could not fix but just inform the  
> error by
>    filling the rd with ~0UL. Could you explain why should we care  
> about the update?

If you're emulating the instruction, you need to handle all of that  
instruction's effects.  If you're not going to emulate the instruction,  
don't skip it.

-Scott