Re: [PATCH] x86/shadow: Delete the none.c dummy file

[Jan Beulich <jbeulich@xxxxxxxx>]

On 09.02.2026 16:55, Roger Pau Monné wrote:
> On Mon, Feb 09, 2026 at 04:35:04PM +0100, Alejandro Vallejo wrote:
>> On Mon Feb 9, 2026 at 3:42 PM CET, Roger Pau Monné wrote:
>>> On Mon, Feb 09, 2026 at 11:41:02AM +0100, Alejandro Vallejo wrote:
>>>> It only has 2 callers, both of which can be conditionally removed.
>>>>
>>>> Signed-off-by: Alejandro Vallejo <alejandro.garciavallejo@xxxxxxx>
>>>> ---
>>>> I'd be ok conditionalising the else branch on...
>>>>
>>>>     IS_ENABLED(CONFIG_SHADOW_PAGING )|| IS_ENABLED(CONFIG_LOG_DIRTY)
>>>>
>>>> logdirty patch: 
>>>> https://lore.kernel.org/xen-devel/20260209103118.5885-1-alejandro.garciavallejo@xxxxxxx
>>>>
>>>> ... to avoid the danger of stale pointers, with required changes elsewhere 
>>>> so
>>>> none.c is only compiled out in that case.
>>>>
>>>> I'm not sure how much it matters seeing how they are all unreachable.
>>>> ---
>>>>  xen/arch/x86/mm/Makefile        |  2 +-
>>>>  xen/arch/x86/mm/paging.c        |  4 +-
>>>>  xen/arch/x86/mm/shadow/Makefile |  4 --
>>>>  xen/arch/x86/mm/shadow/none.c   | 77 ---------------------------------
>>>>  4 files changed, 3 insertions(+), 84 deletions(-)
>>>>  delete mode 100644 xen/arch/x86/mm/shadow/none.c
>>>>
>>>> diff --git a/xen/arch/x86/mm/Makefile b/xen/arch/x86/mm/Makefile
>>>> index 960f6e8409..066c4caff3 100644
>>>> --- a/xen/arch/x86/mm/Makefile
>>>> +++ b/xen/arch/x86/mm/Makefile
>>>> @@ -1,4 +1,4 @@
>>>> -obj-y += shadow/
>>>> +obj-$(CONFIG_SHADOW_PAGING) += shadow/
>>>>  obj-$(CONFIG_HVM) += hap/
>>>>  
>>>>  obj-$(CONFIG_ALTP2M) += altp2m.o
>>>> diff --git a/xen/arch/x86/mm/paging.c b/xen/arch/x86/mm/paging.c
>>>> index 2396f81ad5..5f70254cec 100644
>>>> --- a/xen/arch/x86/mm/paging.c
>>>> +++ b/xen/arch/x86/mm/paging.c
>>>> @@ -634,7 +634,7 @@ int paging_domain_init(struct domain *d)
>>>>       */
>>>>      if ( hap_enabled(d) )
>>>>          hap_domain_init(d);
>>>> -    else
>>>> +    else if ( IS_ENABLED(CONFIG_SHADOW_PAGING) )
>>>>          rc = shadow_domain_init(d);
>>>
>>> If you want to go this route you will need to set rc = -EOPNOTSUPP;
>>> prior to the `if ... else if` on the HVM case.
>>
>> Maybe this instead
>>
>>     else
>>         rc = IS_ENABLED(PV) ? shadow_domain_init(d) : -EOPNOTSUPP;
> 
> But even for the PV case we cannot call shadow_domain_init() if shadow
> is compiled out?  I think you want:
> 
>     if ( hap_enabled(d) )
>         hap_domain_init(d);
>     else if ( IS_ENABLED(CONFIG_SHADOW_PAGING) )
>         rc = shadow_domain_init(d);
>     else
>         rc = is_hvm_domain(d) ? -EOPNOTSUPP : 0;

Wouldn't this still leave NULL pointers in places where they can be rather
dangerous with PV guests?

Jan