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

[Michael S. Tsirkin]

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.

Producing another 4 bytes is not really the issue, the issue
is how does guest consume this.
So I would like this discussion to happen on the linux kernel mailing
list not just here.  Can you post the linux patch please?




> Babis Chalios (2):
>   vmgenid: make device data size configurable
>   vmgenid: add generation counter
> 
>  docs/specs/vmgenid.txt    | 101 ++++++++++++++++++--------
>  hw/acpi/vmgenid.c         | 145 +++++++++++++++++++++++++++++++-------
>  include/hw/acpi/vmgenid.h |  23 ++++--
>  3 files changed, 204 insertions(+), 65 deletions(-)
> 
> -- 
> 2.37.1
> 
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