Re: [PATCH v3 02/70] RAMBlock: Add support of KVM private guest memfd

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On 11/16/2023 1:54 AM, David Hildenbrand wrote:
On 15.11.23 08:14, Xiaoyao Li wrote:
Add KVM guest_memfd support to RAMBlock so both normal hva based memory
and kvm guest memfd based private memory can be associated in one RAMBlock.

Introduce new flag RAM_GUEST_MEMFD. When it's set, it calls KVM ioctl to
create private guest_memfd during RAMBlock setup.

Note, RAM_GUEST_MEMFD is supposed to be set for memory backends of
confidential guests, such as TDX VM. How and when to set it for memory
backends will be implemented in the following patches.

Can you elaborate (and add to the patch description if there is good reason) why we need that flag and why we cannot simply rely on the VM type instead to decide whether to allocate a guest_memfd or not?


The reason is, relying on the VM type is sort of hack that we need to get the MachineState instance and retrieve the vm type info. I think it's better not to couple them.

More importantly, it's not flexible and extensible for future case that not all the memory need guest memfd.




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