Re: [PATCH 0/2] vmgenid: add generation counter

["Jason A. Donenfeld" <Jason@zx2c4.com>]

Hi Babis,

On Wed, Aug 03, 2022 at 03:41:45PM +0200, bchalios@amazon.es wrote:
> From: Babis Chalios <bchalios@amazon.es>
> 
> VM generation ID exposes a GUID inside the VM which changes every time a
> VM restore is happening. Typically, this GUID is used by the guest
> kernel to re-seed its internal PRNG. As a result, this value cannot be
> exposed in guest user-space as a notification mechanism for VM restore
> events.
> 
> This patch set extends vmgenid to introduce a 32 bits generation counter
> whose purpose is to be used as a VM restore notification mechanism for
> the guest user-space.
> 
> It is true that such a counter could be implemented entirely by the
> guest kernel, but this would rely on the vmgenid ACPI notification to
> trigger the counter update, which is inherently racy. Exposing this
> through the monitor allows the updated value to be in-place before
> resuming the vcpus, so interested user-space code can (atomically)
> observe the update without relying on the ACPI notification.

As I wrote on LKML:
https://lore.kernel.org/lkml/Yuve4vuAnU85mdRY@zx2c4.com/
you seem to be rehashing something already discussed in earlier threads.
I don't think we should rush to adding something like this to QEMU.

Jason