Re: [PATCH] x86/ucode/AMD: apply the patch early on every logical thread

[Sergey Dyasli <sergey.dyasli@xxxxxxxxx>]

On Thu, Jan 5, 2023 at 10:56 PM Andrew Cooper <Andrew.Cooper3@xxxxxxxxxx> wrote:
> > diff --git a/xen/arch/x86/cpu/microcode/private.h 
> > b/xen/arch/x86/cpu/microcode/private.h
> > index 73b095d5bf..c4c6729f56 100644
> > --- a/xen/arch/x86/cpu/microcode/private.h
> > +++ b/xen/arch/x86/cpu/microcode/private.h
> > @@ -7,6 +7,7 @@ extern bool opt_ucode_allow_same;
> >
> >  enum microcode_match_result {
> >      OLD_UCODE, /* signature matched, but revision id is older or equal */
> > +    SAME_UCODE, /* signature matched, but revision id is the same */
> >      NEW_UCODE, /* signature matched, but revision id is newer */
> >      MIS_UCODE, /* signature mismatched */
> >  };
>
> I don't think this is a clever idea.  For one, OLD and SAME are now
> ambiguous (at least as far as the comments go), and having the
> difference between the two depend on allow_same is unexpected to say the
> least.

Sorry I missed that "equal" comment which is easily removable. What I
don't follow is your concern about allow_same. It's already changing
if OLD/NEW is returned and my patch makes it SAME/NEW.

> I never really liked the enum to begin with, and I think the logic would
> be cleaner without it.
>
>
> We depend entirely on there being one ucode blob which is applicable
> globally across the system, so MIS_UCODE can be expressed as returning
> NULL from the initial searches.  Everything else can then be expressed
> in a normal {mem,str}cmp() way (i.e. -1/0/+1).

This idea sounds good but in practice there are vendor-specific functions
which return enum microcode_match_result and I don't see how it could be
easily replaced with NULL/-1/0/+1 without code changes. I also find the
enum values easier to read.

Sergey