Re: [Xen-devel] [PATCH 2/2] microcode: Check whether the microcode is correct.

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Wed, Sep 25, 2013 at 02:13:40PM +0100, Andrew Cooper wrote:
> On 25/09/13 13:57, Konrad Rzeszutek Wilk wrote:
> > We do the microcode code update in two steps - the presmp:
> >  'microcode_presmp_init' and when CPUs are brought up:
> > 'microcode_init'. The earlier performs the microcode update
> > on the BSP - but unfortunately it does not check whether the
> > update failed. Which means that we might try later to update
> > a incorrect payload on the rest of CPUs.
> >
> > This patch handles this odd situation.
> >
> > Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> 
> While not strictly relevant to this patch, I simply noticed when
> reviewing it that ucode_blob is __initdata.  Given the comment "The
> cached microcode patch is applied when CPUs resume from a sleep state."
> in the previous patch, what is the policy for reloading microcode after
> deep sleep / cpu hotplug ?

The underlaying architecture microcode (microcode_intel or microcode_amd)
end up saving it in 'struct ucode_cpu_info' which is a per-cpu data
structure (see ucode_cpu_info). They end up saving it when doing the
pre-SMP (for CPU0) and SMP (for the rest) microcode loading.

And naturally if one does a hypercall to update the microcode and it is
newer, then the old per-cpu data is replaced.

Would you like me to update the git commit description with this?
> 
> > [v2: Redid it as we are not doing scan and <index> at the same time]
> > ---
> >  xen/arch/x86/microcode.c | 16 +++++++++++++++-
> >  1 file changed, 15 insertions(+), 1 deletion(-)
> >
> > diff --git a/xen/arch/x86/microcode.c b/xen/arch/x86/microcode.c
> > index 8136d44..0bc95e6 100644
> > --- a/xen/arch/x86/microcode.c
> > +++ b/xen/arch/x86/microcode.c
> > @@ -419,6 +419,7 @@ static int __init microcode_presmp_init(void)
> >          {
> >              void *data;
> >              size_t len;
> > +            int rc = 0;
> >  
> >              if ( ucode_blob.size )
> >              {
> > @@ -431,10 +432,23 @@ static int __init microcode_presmp_init(void)
> >                  data = ucode_mod_map(&ucode_mod);
> >              }
> >              if ( data )
> > -                microcode_update_cpu(data, len);
> > +                rc = microcode_update_cpu(data, len);
> > +            else
> > +                rc = -ENOMEM;
> >  
> >              if ( !ucode_blob.size )
> >                  ucode_mod_map(NULL);
> > +
> > +            if ( rc )
> > +            {
> > +                if ( ucode_blob.size )
> > +                {
> > +                    xfree(ucode_blob.data);
> > +                    ucode_blob.size = 0;
> > +                    ucode_blob.data = NULL;
> > +                } else
> > +                    ucode_mod.mod_end = 0;
> > +            }
> >          }
> >  
> >          register_cpu_notifier(&microcode_percpu_nfb);
> 

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