Re: [PATCH v4 2/2] x86/monitor: Add new monitor event to catch all vmexits

[Tamas K Lengyel <tamas@xxxxxxxxxxxxx>]

On Wed, Apr 13, 2022 at 9:43 AM Tamas K Lengyel <tamas.lengyel@xxxxxxxxx> wrote:
>
> Add monitor event that hooks the vmexit handler allowing for both sync and
> async monitoring of events. With async monitoring an event is placed on the
> monitor ring for each exit and the rest of the vmexit handler resumes 
> normally.
> If there are additional monitor events configured those will also place their
> respective events on the monitor ring.
>
> With the sync version an event is placed on the monitor ring but the handler
> does not get resumed, thus the sync version is only useful when the VM is not
> expected to resume normally after the vmexit. Our use-case is primarily with
> the sync version with VM forks where the fork gets reset after sync vmexit
> event, thus the rest of the vmexit handler can be safely skipped. This is
> very useful when we want to avoid Xen crashing the VM under any circumstance,
> for example during fuzzing. Collecting all vmexit information regardless of
> the root cause makes it easier to reason about the state of the VM on the
> monitor side, hence we opt to receive all events, even for external interrupt
> and NMI exits and let the monitor agent decide how to proceed.
>
> Signed-off-by: Tamas K Lengyel <tamas.lengyel@xxxxxxxxx>
> ---
> v4: Minor tweaks and more verbose patch description.
>
> Note: making the sync version resume-friendly is specifically out-of-scope as
> it would require significant rearrangement of the vmexit handler. As this
> feature is not required for our use-case we opt for the version that minimizes
> impact on the existing code.

Patch ping.