Re: [Xen-devel] [PATCH v7 02/10] microcode/intel: extend microcode_update_match()

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

On Tue, Jun 04, 2019 at 08:39:15AM -0600, Jan Beulich wrote:
> >>> On 27.05.19 at 10:31, <chao.gao@xxxxxxxxx> wrote:
> > --- a/xen/arch/x86/microcode_intel.c
> > +++ b/xen/arch/x86/microcode_intel.c
> > @@ -134,14 +134,28 @@ static int collect_cpu_info(unsigned int cpu_num, 
> > struct cpu_signature *csig)
> >      return 0;
> >  }
> >  
> > -static inline int microcode_update_match(
> > -    unsigned int cpu_num, const struct microcode_header_intel *mc_header,
> > -    int sig, int pf)
> > +static enum microcode_match_result microcode_update_match(
> > +    const struct microcode_header_intel *mc_header, unsigned int sig,
> > +    unsigned int pf, unsigned int rev)
> >  {
> > -    struct ucode_cpu_info *uci = &per_cpu(ucode_cpu_info, cpu_num);
> > +    const struct extended_sigtable *ext_header;
> > +    const struct extended_signature *ext_sig;
> > +    unsigned long data_size = get_datasize(mc_header);
> > +    unsigned int i;
> > +
> > +    if ( sigmatch(sig, mc_header->sig, pf, mc_header->pf) )
> > +        return (mc_header->rev > rev) ? NEW_UCODE : OLD_UCODE;
> 
> As indicated before, I think you would better also provide an "equal"
> indication. Iirc I've told you that I have one system where the cores
> get handed over from the BIOS in an inconsistent state (only core
> has ucode loaded). Hence we'd want to be able to also _store_
> ucode matching that found on CPU 0, without actually want to _load_
> it there.

Hm, without me being an expert on microcode, isn't such a system utterly
broken?

I'm not against making Xen capable of booting in this scenario where
firmware leaves the CPUs with different microcode versions, but this
is something that should be reported to the vendor in order to get it
fixed IMO?

What happens when you don't load any microcode at all, is the system
capable of operating normally with such mixed microcode?

Thanks, Roger.

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