Re: [PATCH 2/2] x86/tdx: Accept hotplugged memory before online

[David Hildenbrand (Arm)]

On 3/27/26 04:05, Chenyi Qiang wrote:
> 
> 
> On 3/25/2026 6:29 PM, Marc-André Lureau wrote:
>> Hi
>>
>> On Wed, Mar 25, 2026 at 2:04 AM Edgecombe, Rick P
>> <rick.p.edgecombe@xxxxxxxxx> wrote:
>>>
>>>
>>> Does this depend on patch 1 somehow?
>>
>> Yes, if I plug, unplug and plug again I get this without PATCH 1:
>> [root@rhel10-server ~]# [ 5707.392231] virtio_mem virtio5: plugged
>> size: 0x80000000
>> [ 5707.395583] virtio_mem virtio5: requested size: 0x0
>>
>> [root@rhel10-server ~]# [ 5714.648501] virtio_mem virtio5: plugged
>> size: 0x2e00000
>> [ 5714.651808] virtio_mem virtio5: requested size: 0x80000000
>> [ 5714.676296] tdx: Failed to accept memory [0x108000000, 0x110000000)
>> [ 5714.683980] tdx: Failed to accept memory [0x110000000, 0x118000000)
>> [ 5714.686997] tdx: Failed to accept memory [0x140000000, 0x148000000)
>> [ 5714.689989] tdx: Failed to accept memory [0x128000000, 0x130000000)
>> [ 5714.694981] tdx: Failed to accept memory [0x148000000, 0x150000000)
>> [ 5714.704064] tdx: Failed to accept memory [0x138000000, 0x140000000)
>> [ 5714.710144] tdx: Failed to accept memory [0x118000000, 0x120000000)
>> [ 5714.722532] tdx: Failed to accept memory [0x130000000, 0x138000000)
>>
>> My understanding is that QEMU should eventually unplug the memory and
>> PUNCH_HOLE then KVM should TDH.MEM.PAGE.REMOVE, but that doesn't seem
>> to happen. 
> 
> I guess it doesn't happen because virtio-mem in QEMU only PUNCH_HOLE the
> shared memory by ram_block_discard_range() but it doesn't touch the private
> memory which should be discarded by ram_block_discard_guest_memfd_range().
> 
> Is this strictly required? According to the specification,

So far nobody specified how virtio-mem should behave in a CoCo environment.

I assume that we need enhancements on the driver and the device side.

In Linux, we should not be accepting memory during memory
onlining/offlining through notifiers, as we might only hot(un)plug parts
of a memory block etc.

We need some explicit calls into the core before we hand hotplugged
memory to the core, and before we hand back unplugged memory to the device.

In QEMU, I would similarly assume that we might have to perform some
additional work when converting memory blocks. *maybe* that would just
be done by the guest that converts memory from private to shared before
unplug etc.

-- 
Cheers,

David