Re: [PATCH v7 06/14] KVM: Add memslot flag to let userspace force an exit on missing hva mappings

[Nikita Kalyazin <kalyazin@amazon.com>]

Hi David,

On 11/03/2024 16:20, David Matlack wrote:
> On Sun, Mar 10, 2024 at 9:46 PM Oliver Upton <oliver.upton@linux.dev> wrote:
>>>>
>>>>    2. What is your best guess as to when KVM userfault patches will be available,
>>>>       even if only in RFC form?
>>>
>>> We're aiming for the end of April for RFC with KVM/ARM support.
>>
>> Just to make sure everyone is read in on what this entails -- is this
>> the implementation that only worries about vCPUs touching non-present
>> memory, leaving the question of other UAPIs that consume guest memory
>> (e.g. GIC/ITS table save/restore) up for further discussion?
> 
> Yes. The initial version will only support returning to userspace on
> invalid vCPU accesses with KVM_EXIT_MEMORY_FAULT. Non-vCPU accesses to
> invalid pages (e.g. GIC/ITS table save/restore) will trigger an error
> return from __gfn_to_hva_many() (which will cause the corresponding
> ioctl to fail). It will be userspace's responsibility to clear the
> invalid attribute before invoking those ioctls.
> 
> For x86 we may need an blocking kernel-to-userspace notification
> mechanism for code paths in the emulator, but we'd like to investigate
> and discuss if there are any other cleaner alternatives before going
> too far down that route.

I wasn't able to locate any follow-ups on the LKML about this topic.
May I know if you are still working on or planning to work on this?

Thanks,
Nikita