Re: [Xen-devel] [PATCH V3] x86, amd_ucode: Support multiple container files appended together

[Aravind Gopalakrishnan <aravind.gopalakrishnan@xxxxxxx>]

On 6/26/2014 8:14 AM, Boris Ostrovsky wrote:
> > +    /*
> > +     * Multiple container file support:
> > +     * 1. check if this container file has equiv_cpu_id match
> > +     * 2. If not, fast-fwd to next container file
> > +     */
> > +    while ( offset < bufsize )
> > +    {
> > +        error = install_equiv_cpu_table(mc_amd, buf, &offset);
> > +
> > +        if ( !error &&
> > +             find_equiv_cpu_id(mc_amd->equiv_cpu_table, current_cpu_id,
> > +                               &equiv_cpu_id) )
> > +                break;
> > +
> > +        /*
> > +         * Could happen as we advance 'offset' early
> > +         * in install_equiv_cpu_table
> > +         */
> > +        if ( offset > bufsize )
> > +        {
> > +            printk(KERN_ERR "microcode: Microcode buffer overrun\n");
> > +            return -EINVAL;
> > +        }
> > +
> > +        error = container_fast_forward(buf, bufsize - offset, &offset);
> > +        if ( error )
> > +        {
> > +            printk(KERN_ERR "microcode: CPU%d incorrect or corrupt 
> > container file\n"
> > +                   "microcode: Failed to update patch level. "
> > +                   "Current lvl:%#x\n", cpu, uci->cpu_sig.rev);
> > +            goto out;
> > +        }
> > +    }
> > +
> I just realized that I don't understand something: if you have two 
> merged container files, both having an entry for current processor in 
> the equivalence table but only the second file having the actual patch 
> (or at least the patch with higher version), will we get to load that 
> patch?
We will not come across such a situation:
One container has patch files for families 10h,11h,12h,14h and the other 
has patches for 15h.
So there will be an equiv_cpu_id match in (at least and) only *one* of 
the containers.
(If there ever are patches for 16h, then I suspect it will have a 
separate container of it's own. So there will not be any clashes with 
older containers)
Besides, the patches themselves are not incremental, i.e;
If there is a newer patch, then it handles all errata/bugs that were 
handled by the previous patch and then some.
Which means, you will not have a container that has two patches for the 
same processor.
So, *strictly speaking*, even the loop to get_ucode_from_buffer_amd() 
till the end of buffer is not necessary once we
have already applied a patch.

But, to change this behavior now will need more logic rework..
Then again, if it works fine right now, would we really want to change 
this behavior?
Thanks,
-Aravind.

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