Re: [PATCH v6] x86: detect CMOS aliasing on ports other than 0x70/0x71

["Roger Pau Monné" <roger.pau@citrix.com>]

On Wed, Apr 19, 2023 at 09:56:35AM +0200, Jan Beulich wrote:
> On 18.04.2023 13:35, Roger Pau Monné wrote:
> > On Tue, Apr 18, 2023 at 11:24:19AM +0200, Jan Beulich wrote:
> >> ... in order to also intercept Dom0 accesses through the alias ports.
> >>
> >> Also stop intercepting accesses to the CMOS ports if we won't ourselves
> >> use the CMOS RTC, because of there being none.
> >>
> >> Note that rtc_init() deliberately uses 16 as the upper loop bound,
> >> despite probe_cmos_alias() using 8: The higher bound is benign now, but
> >> would save us touching the code (or, worse, missing to touch it) in case
> >> the lower one was doubled.
> >>
> >> Signed-off-by: Jan Beulich <jbeulich@suse.com>
> > 
> > Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>
> 
> Thanks.
> 
> >> --- a/xen/arch/x86/pv/emul-priv-op.c
> >> +++ b/xen/arch/x86/pv/emul-priv-op.c
> >> @@ -208,7 +208,7 @@ static bool admin_io_okay(unsigned int p
> >>          return false;
> >>  
> >>      /* We also never permit direct access to the RTC/CMOS registers. */
> > 
> > Hm, it's unclear to me whether the comment above would need updating:
> > we don't allow direct access to the RTC/CMOS registers, but we allow
> > direct access to the RTC/CMOS ports if there's no device behind.
> 
> Right, but those ports then don't allow access to said registers. So
> I think the comment is fine as is.

Yes, that's why I wasn't really sure whether to comment.  The comment
is formally correct, but it might lead to confusion if one doesn't
carefully read 'RTC/CMOS registers' (vs RTC/CMOS IO ports).

Anyway, sorry for the noise.

Thanks, Roger.