Re: [Xen-devel] [PATCH v4 2/6] microcode: save all microcodes which pass sanity check

["Woods, Brian" <Brian.Woods@xxxxxxx>]

On Thu, Nov 29, 2018 at 10:22:10AM +0100, Roger Pau Monné wrote:
> On Thu, Nov 29, 2018 at 10:40:32AM +0800, Chao Gao wrote:
> > On Wed, Nov 28, 2018 at 01:00:14PM +0100, Roger Pau Monné wrote:
> > >On Wed, Nov 28, 2018 at 01:34:12PM +0800, Chao Gao wrote:
> > >> ... and search caches to find a suitable one when loading.
> > >
> > >Why do you need to save all of them? You are only going to load a
> > >single microcode, so I don't understand the need to cache them all.
> 
> I think the above question needs an answer.
> 
> > >IMO making such modifications to the AMD code without testing it is
> > >very dangerous. Could you get an AMD system or ask an AMD dev to test
> > >it? I would try with the AMD SVM maintainers.
> > 
> > It is improbable for me to find an AMD machine in my team. I will copy AMD
> > SVM maintainers in the coming versions and ask them to help to test this
> > series.
> 
> I'm Cc'ing them now in case they want to provide some feedback.
> 
> > >> +static int save_patch(struct ucode_patch *new_patch)
> > >> +{
> > >> +    struct ucode_patch *ucode_patch;
> > >> +    struct microcode_amd *new_mc = new_patch->data;
> > >> +    struct microcode_header_amd *new_header = new_mc->mpb;
> > >> +
> > >> +    list_for_each_entry(ucode_patch, &microcode_cache, list)
> > >> +    {
> > >> +        struct microcode_amd *old_mc = ucode_patch->data;
> > >> +        struct microcode_header_amd *old_header = old_mc->mpb;
> > >> +
> > >> +        if ( new_header->processor_rev_id == 
> > >> old_header->processor_rev_id )
> > >> +        {
> > >> +            if ( new_header->patch_id <= old_header->patch_id )
> > >> +                return -1;
> > >> +            list_replace(&ucode_patch->list, &new_patch->list);
> > >> +            free_ucode_patch(ucode_patch);
> > >> +            return 0;
> > >> +        }
> > >> +    }
> > >
> > >This could be made common code with a specific hook for AMD and Intel
> > >in order to do the comparison, so that at least the loop over the
> > >list of ucode entries could be shared.
> > 
> > Something like pt_pirq_iterate()? Will give it a try.
> 
> Yes, that might also be helpful. I was thinking of adding such a
> comparison hook in microcode_ops, also having something like
> pt_pirq_iterate will be helpful if you need to iterate over the cache
> in other functions.
> 
> > >> @@ -491,6 +559,21 @@ static int cpu_request_microcode(unsigned int cpu, 
> > >> const void *buf,
> > >>      while ( (error = get_ucode_from_buffer_amd(mc_amd, buf, bufsize,
> > >>                                                 &offset)) == 0 )
> > >>      {
> > >> +        struct ucode_patch *ucode_patch;
> > >> +
> > >> +        /*
> > >> +         * Save this microcode before checking the signature. It is to
> > >> +         * optimize microcode update on a mixed family system. Parsing
> > >
> > >Er, is it possible to have a system with CPUs of different family?
> > >What's going to happen with CPUs having different features?
> > 
> > I have no idea. That each cpu has a per-cpu variable to store the
> > microcode rather than a global one gives me a feeling that the current
> > implementation wants to make it work on a system with CPUs of different
> > family.
> 
> I think we need AMD maintainers input on this one. TBH I very much
> doubt there are (working) systems out there with mixed family CPUs.
> 
> Thanks, Roger.

Sorry about the delay.  From the PPR for F17 M00-0FH
"AMD Family 17h processors with different OPNs or different revisions
cannot be mixed in a multiprocessor system. If an unsupported
configuration is detected, BIOS should configure the BSP as a single
processor system and signal an error."

Even mixing OPNs within a model is a no go for us.  Mixing different
families is something I highly doubt will ever be supported.

-- 
Brian Woods

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxxx
https://lists.xenproject.org/mailman/listinfo/xen-devel