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

[bchalios]

On 8/3/22 5:36 PM, "Michael S. Tsirkin" <mst@redhat.com> wrote:
> CAUTION: This email originated from outside of the organization. Do not click 
> links or open attachments unless you can confirm the sender and know the 
> content is safe.
>
>
>
> 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?

CCed you in the Linux patch thread.

> > 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
> >
> > Amazon Spain Services sociedad limitada unipersonal, Calle Ramirez de Prado 
> 5, 28045 Madrid. Registro Mercantil de Madrid . Tomo 22458 . Folio 102 . Hoja 
> M-401234 . CIF B84570936
Amazon Spain Services sociedad limitada unipersonal, Calle Ramirez de Prado 5, 
28045 Madrid. Registro Mercantil de Madrid . Tomo 22458 . Folio 102 . Hoja 
M-401234 . CIF B84570936