Ping: [PATCH v4] x86/shim: don't permit HVM and PV_SHIM_EXCLUSIVE at the same time

[Jan Beulich <jbeulich@xxxxxxxx>]

On 15.04.2021 11:27, Jan Beulich wrote:
> This combination doesn't really make sense (and there likely are more);
> in particular even if the code built with both options set, HVM guests
> wouldn't work (and I think one wouldn't be able to create one in the
> first place). The alternative here would be some presumably intrusive
> #ifdef-ary to get this combination to actually build (but still not
> work) again.
> 
> Fixes: 8b5b49ceb3d9 ("x86: don't include domctl and alike in shim-exclusive 
> builds")
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> Acked-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>

Andrew,

I know you're not happy with this change, but I also don't recall
you proposing any sufficiently straightforward alternative. Nor do
I recall you responding to my claim that the combination is useless
anyway, since the PV shim exists solely to create a single PV guest.
Since I have Roger's ack, may I ask that you firmly NACK the change
here (accompanied by an alternative proposal), if you're really
convinced that your view on the situation is the only sensible one?
If I don't hear back by the end of the week, I guess I'll put the
change in early next week.

Jan


> ---
> v4: Default HVM to !PV_SHIM, as suggested by Jürgen.
> v2: Restore lost default setting.
> 
> --- a/xen/arch/x86/Kconfig
> +++ b/xen/arch/x86/Kconfig
> @@ -23,7 +23,7 @@ config X86
>       select HAS_PDX
>       select HAS_SCHED_GRANULARITY
>       select HAS_UBSAN
> -     select HAS_VPCI if !PV_SHIM_EXCLUSIVE && HVM
> +     select HAS_VPCI if HVM
>       select NEEDS_LIBELF
>       select NUMA
>  
> @@ -90,9 +90,10 @@ config PV_LINEAR_PT
>           If unsure, say Y.
>  
>  config HVM
> -     def_bool !PV_SHIM_EXCLUSIVE
> +     bool "HVM support"
> +     depends on !PV_SHIM_EXCLUSIVE
> +     default !PV_SHIM
>       select IOREQ_SERVER
> -     prompt "HVM support"
>       ---help---
>         Interfaces to support HVM domains.  HVM domains require hardware
>         virtualisation extensions (e.g. Intel VT-x, AMD SVM), but can boot
>