Re: [PATCH] x86/boot: Further simplify CR4 handling in dom0_construct_pv()

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

On Fri, Oct 04, 2024 at 08:52:52AM +0200, Jan Beulich wrote:
> On 03.10.2024 01:20, Andrew Cooper wrote:
> > The logic would be more robust disabling SMAP based on its precense in CR4,
> > rather than SMAP's accociation with a synthetic feature.
> 
> It's hard to tell what's more robust without knowing what future changes
> there might be. In particular ...
> 
> > @@ -1064,19 +1065,19 @@ int __init dom0_construct_pv(struct domain *d,
> >       * prevents us needing to write construct_dom0() in terms of
> >       * copy_{to,from}_user().
> >       */
> > -    if ( boot_cpu_has(X86_FEATURE_XEN_SMAP) )
> > +    if ( cr4 & X86_CR4_SMAP )
> 
> ... with this adjustment ...
> 
> >      {
> >          if ( IS_ENABLED(CONFIG_PV32) )
> >              cr4_pv32_mask &= ~X86_CR4_SMAP;
> 
> ... this update of a global no longer occurs. Playing games with CR4
> elsewhere might run into issues with this lack of updating.

Maybe we should assert the state of cr4 is as expected?

ASSERT(!boot_cpu_has(X86_FEATURE_XEN_SMAP) || (cr4 & X86_CR4_SMAP));

Thanks, Roger.