Re: [PATCH] ptp: Add vDSO-style vmclock support

[Michael S. Tsirkin]

On Wed, Jul 24, 2024 at 06:16:37PM +0100, David Woodhouse wrote:
> From: David Woodhouse <dwmw@amazon.co.uk>
> 
> The vmclock "device" provides a shared memory region with precision clock
> information. By using shared memory, it is safe across Live Migration.
> 
> Like the KVM PTP clock, this can convert TSC-based cross timestamps into
> KVM clock values. Unlike the KVM PTP clock, it does so only when such is
> actually helpful.
> 
> The memory region of the device is also exposed to userspace so it can be
> read or memory mapped by application which need reliable notification of
> clock disruptions.
> 
> Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>

one other thing worth mentioning is that this design can't work
with confidential computing setups. By comparison, mapping e.g. a
range in a PCI BAR would work for these setups.
Is there a reason this functionality is not interesting for
confidential VMs?

-- 
MST