Re: [PATCH 2/3] xen/arm, tools: Add a new HVM_PARAM_MAGIC_BASE_PFN key in HVMOP

[Henry Wang <xin.wang2@xxxxxxx>]

Hi Jan,

On 4/30/2024 2:11 PM, Jan Beulich wrote:
> On 30.04.2024 04:51, Henry Wang wrote:
> > On 4/30/2024 8:31 AM, Daniel P. Smith wrote:
> > > On 4/26/24 02:21, Jan Beulich wrote:
> > > > On 26.04.2024 05:14, Henry Wang wrote:
> > > > > --- a/xen/include/public/hvm/params.h
> > > > > +++ b/xen/include/public/hvm/params.h
> > > > > @@ -76,6 +76,7 @@
> > > > >     */
> > > > >    #define HVM_PARAM_STORE_PFN    1
> > > > >    #define HVM_PARAM_STORE_EVTCHN 2
> > > > > +#define HVM_PARAM_MAGIC_BASE_PFN    3
> > > > >      #define HVM_PARAM_IOREQ_PFN    5
> > > > Considering all adjacent values are used, it is overwhelmingly likely
> > > > that
> > > > 3 was once used, too. Such re-use needs to be done carefully. Since you
> > > > need this for Arm only, that's likely okay, but doesn't go without (a)
> > > > saying and (b) considering the possible future case of dom0less becoming
> > > > arch-agnostic, or hyperlaunch wanting to extend the scope. Plus (c) imo
> > > > this also needs at least a comment, maybe even an #ifdef, seeing how
> > > > x86-
> > > > focused most of the rest of this header is.
> > > I would recommend having two new params,
> > Sounds good. I can do the suggestion in v2.
> >
> > > #define HVM_PARAM_HV_RSRV_BASE_PVH 3
> > > #define HVM_PARAM_HV_RSRV_SIZE 4
> > I think 4 is currently in use, so I think I will find another couple of
> > numbers in the end for both of them. Instead of reusing 3 and 4.
> Right. There are ample gaps, but any use of values within a gap will need
> appropriate care. FTAOD using such a gap looks indeed preferable, to avoid
> further growing the (sparse) array. Alternatively, if we're firm on this
> never going to be used on x86, some clearly x86-specific indexes (e.g. 36
> and 37) could be given non-x86 purpose.
Sorry, I am a bit confused. I take Daniel's comment as to add two new 
params, which is currently only used for Arm, but eventually will be 
used for hyperlaunch on x86 (as the name indicated). So I think I will 
use the name that he suggested, but the number changed to 39 and 40.
Kind regards,
Henry

> Jan