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

[Chenyi Qiang]

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:
>>
>> On Tue, 2026-03-24 at 19:21 +0400, Marc-André Lureau wrote:
>>> In TDX guests, hotplugged memory (e.g., via virtio-mem) is never
>>> accepted before use. The first access triggers a fatal "SEPT entry in
>>> PENDING state" EPT violation and KVM terminates the guest.
>>>
>>> Fix this by registering a MEM_GOING_ONLINE memory hotplug notifier that
>>> calls tdx_accept_memory() for the range being onlined.
>>>
>>> The notifier returns NOTIFY_BAD on acceptance failure, preventing the
>>> memory from going online.
>>
>> 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,
> it may not be.
> 
>