Re: [PATCH] x86/hvm: Fix fast singlestep state persistence

[Tamas K Lengyel <tamas@xxxxxxxxxxxxx>]

On Thu, Feb 8, 2024 at 4:20 PM Petr Beneš <w1benny@xxxxxxxxx> wrote:
>
> From: Petr Beneš <w1benny@xxxxxxxxx>
>
> This patch addresses an issue where the fast singlestep setting would persist
> despite xc_domain_debug_control being called with 
> XEN_DOMCTL_DEBUG_OP_SINGLE_STEP_OFF.
> Specifically, if fast singlestep was enabled in a VMI session and that session
> stopped before the MTF trap occurred, the fast singlestep setting remained
> active even though MTF itself was disabled.  This led to a situation where, 
> upon
> starting a new VMI session, the first event to trigger an EPT violation would
> cause the corresponding EPT event callback to be skipped due to the lingering
> fast singlestep setting.
>
> The fix ensures that the fast singlestep setting is properly reset when
> disabling single step debugging operations.
>
> Signed-off-by: Petr Beneš <w1benny@xxxxxxxxx>

Thanks, this has been a known bug that awaited a fix for a long time.

Reviewed-by: Tamas K Lengyel <tamas@xxxxxxxxxxxxx>