Re: [Xen-devel] [PATCH v2] psr: fix bug which may cause crash

[Yi Sun <yi.y.sun@xxxxxxxxxxxxxxx>]

On 19-11-28 12:25:44, Jan Beulich wrote:
> On 28.11.2019 11:18, Yi Sun wrote:
> > --- a/xen/arch/x86/psr.c
> > +++ b/xen/arch/x86/psr.c
> > @@ -1271,7 +1271,8 @@ static void do_write_psr_msrs(void *data)
> >  
> >          for ( j = 0; j < cos_num; j++, index++ )
> >          {
> > -            if ( feat->cos_reg_val[cos * cos_num + j] != info->val[index] )
> > +            if ( cos <= feat->cos_max &&
> > +                 feat->cos_reg_val[cos * cos_num + j] != info->val[index] )
> 
> The description is indeed much better now, thanks. However,
> as indicated in reply to v1, this extra (and at the first glance
> unmotivated) bounds check wants to be accompanied by a brief but

I will add the comment.

> precise comment. Furthermore with the loop bounded by a local
> variable, why not
> 
>         cos_num = min(props->cos_num, feat->cos_max + 1);
> 
> a few lines up from here (again suitable commented)?
>
cos_num is a different thing with the number of COS registers. The
meaning of it is "COS registers number that feature uses for one COS
ID". E.g. MBA/CAT cos_num is always 1. But CDP cos_num is 2 because it
uses 2 COS registers for one COS ID.
 
> Jan

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