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

[Jia Hongtao-B38951]

> -----Original Message-----
> From: Wood Scott-B07421
> Sent: Friday, March 08, 2013 12:38 AM
> To: Jia Hongtao-B38951
> Cc: David Laight; Wood Scott-B07421; 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 03/07/2013 02:06:05 AM, Jia Hongtao-B38951 wrote:
> > Here is the ideas from Scott:
> > "
> > > +	if (is_in_pci_mem_space(addr)) {
> > > +		inst = *(unsigned int *)regs->nip;
> >
> > Be careful about taking a fault here.  A simple TLB miss should be
> > safe given that we shouldn't be accessing PCIe in the middle of
> > exception code, but what if the mapping has gone away (e.g. a
> > userspace driver had its code munmap()ed or swapped out)?  What if
> > permissions allow execute but not read (not sure if Linux will allow
> > this, but the hardware does)?
> >
> > What if it happened in a KVM guest?  You can't access guest addresses
> > directly.
> > "
> 
> That means you need to be careful about how you read the instruction, not
> that you shouldn't do it at all.
> 
> -Scott

I agree.

Do you have a more secure way to get the instruction?
Or what should be done to avoid permission break issue?

Thanks.
-Hongtao