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

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Message-ID: <13ca9404-1e4c-4035-8dda-5b628aec3a28@amd.com>
Date: Wed, 14 Jan 2026 16:56:48 -0600
From: "Pratik R. Sampat" <prsampat@....com>
To: "David Hildenbrand (Red Hat)" <david@...nel.org>, linux-mm@...ck.org,
 linux-coco@...ts.linux.dev, x86@...nel.org, linux-kernel@...r.kernel.org
Cc: tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
 dave.hansen@...ux.intel.com, kas@...nel.org, ardb@...nel.org,
 akpm@...ux-foundation.org, osalvador@...e.de, thomas.lendacky@....com,
 michael.roth@....com
Subject: Re: [PATCH v2 1/2] mm/memory_hotplug: Add support to accept memory
 during hot-add



On 1/14/26 4:30 AM, David Hildenbrand (Red Hat) wrote:
> On 1/12/26 21:22, Pratik R. Sampat 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@....com>
>> ---
>>   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>
>>     #include "internal.h"
>>   #include "shuffle.h"
>> @@ -1567,6 +1568,9 @@ int add_memory_resource(int nid, struct resource *res, mhp_t mhp_flags)
>>       if (!strcmp(res->name, "System RAM"))
>>           firmware_map_add_hotplug(start, start + size, "System RAM");
>>   +    if (IS_ENABLED(CONFIG_UNACCEPTED_MEMORY))
>> +        arch_accept_memory(start, start + size);
>> +
>>       /* device_online() will take the lock when calling online_pages() */
>>       mem_hotplug_done();
>>   
> 
> As discussed, for things like virtio-mem or the HV-balloon this might be the wrong thing to do, but I don't expect these mechanisms to be used in CoCo environments just yet (and doing so would require enabling work for them).
> 

Ack.

> So I'm fine with this for now.
> 

Thanks!