Re: [RFC v2 PATCH 01/13] mm/shmem: Introduce F_SEAL_GUEST

[David Hildenbrand]

On 22.11.21 15:01, Jason Gunthorpe wrote:
> On Mon, Nov 22, 2021 at 02:35:49PM +0100, David Hildenbrand wrote:
>> On 22.11.21 14:31, Jason Gunthorpe wrote:
>>> On Mon, Nov 22, 2021 at 10:26:12AM +0100, David Hildenbrand wrote:
>>>
>>>> I do wonder if we want to support sharing such memfds between processes
>>>> in all cases ... we most certainly don't want to be able to share
>>>> encrypted memory between VMs (I heard that the kernel has to forbid
>>>> that). It would make sense in the use case you describe, though.
>>>
>>> If there is a F_SEAL_XX that blocks every kind of new access, who
>>> cares if userspace passes the FD around or not?
>> I was imagining that you actually would want to do some kind of "change
>> ownership". But yeah, the intended semantics and all use cases we have
>> in mind are not fully clear to me yet. If it's really "no new access"
>> (side note: is "access" the right word?) then sure, we can pass the fd
>> around.
> 
> What is "ownership" in a world with kvm and iommu are reading pages
> out of the same fd?

In the world of encrypted memory / TDX, KVM somewhat "owns" that memory
IMHO (for example, only it can migrate or swap out these pages; it's
might be debatable if the TDX module or KVM actually "own" these pages ).

-- 
Thanks,

David / dhildenb