Re: [PATCH v2 1/2] mm/memory_hotplug: Add support to accept memory during hot-add

[Pratik R. Sampat]

On 1/12/26 4:43 PM, Andrew Morton wrote:
> On Mon, 12 Jan 2026 16:23:37 -0600 "Pratik R. Sampat" <prsampat@xxxxxxx> wrote:
> 
>>
>>
>> On 1/12/26 3:04 PM, Andrew Morton wrote:
>>> On Mon, 12 Jan 2026 14:22:59 -0600 "Pratik R. Sampat" <prsampat@xxxxxxx> wrote:
>>>
>>>> Confidential computing guests require memory to be accepted before use.
>>>> The unaccepted memory bitmap maintained by firmware does not track
>>>> hotplugged memory ranges.
>>>>
>>>> Call arch_accept_memory() during the hot-add path to explicitly validate
>>>> and transition the newly added memory to a private state, making it
>>>> usable by the guest.
>>>>
>>>> Signed-off-by: Pratik R. Sampat <prsampat@xxxxxxx>
>>>> ---
>>>>  mm/memory_hotplug.c | 4 ++++
>>>>  1 file changed, 4 insertions(+)
>>>>
>>>> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
>>>> index a63ec679d861..8cfbf0541430 100644
>>>> --- a/mm/memory_hotplug.c
>>>> +++ b/mm/memory_hotplug.c
>>>> @@ -38,6 +38,7 @@
>>>>  #include <linux/node.h>
>>>>  
>>>>  #include <asm/tlbflush.h>
>>>> +#include <asm/unaccepted_memory.h>
>>>
>>> This only exists for x86!
>>
>> Ah, I missed that entirely. Thanks for catching that.
>>
>> Probably not the best option to have a generic unaccepted_memory.h as well.
>> Maybe, I should have arch_[un]accept_memory() definitions within mm.h wrapped
>> within CONFIG_UNACCEPTED_MEMORY instead so that its cleaner.
> 
> Something like that.
> 
> The idiomatic Linus way is to use
> 
> #ifndef arch_accept_memory
> #define arch_accept_memory ...
> #endif
> 
> Lots of prior art here:
> 
> 	grep -r include/linux "ifndef arch_"
> 
> 
> Oh, arch_get_idle_state_flags() got it all wrong.
> 
> 	#ifdef CONFIG_ACPI_PROCESSOR_IDLE
> 	#ifndef arch_get_idle_state_flags
> 	static inline unsigned int arch_get_idle_state_flags(u32 arch_flags)
> 	{
> 		return 0;
> 	}
> 	#endif
> 	#endif /* CONFIG_ACPI_PROCESSOR_IDLE */
> 
> - shouldn't have needed "ifdef CONFIG_ACPI_PROCESSOR_IDLE"
> 
> - should have appended
> 
> 	#define arch_get_idle_state_flags arch_get_idle_state_flags
> 
>   in case cpp hit the same lines a second time.
> 

Got it. Thanks for clearing that up. I'll make sure to do it this way
in the next iteration.

--Pratik