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

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

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.

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