Re: [PATCH 1/3] KVM: SVM: Re-queue events that were never injected

[Sean Christopherson <seanjc@google.com>]

On Mon, Sep 14, 2026, Pratik R. Sampat wrote:
> When injecting an event into the guest via the event_inj field, a
> non-zero event_inj value on #VMEXIT means that the hardware was not able
> to inject the event into the guest.  This used to only occur for the
> VMEXIT_INVALID intercept code, which was a fatal error and resulted in
> the guest being torn down.
> 
> Enhanced SMT Protection (ESMTP) invalidates that assumption.  When ESMTP
> is enabled, VMRUN doesn't enter guest mode immediately; it stalls at a
> synchronization point until every sibling thread is either idle or has
> executed VMRUN for a legal sibling vCPU.  If an ESMTP timeout / illegal
> sibling exit / interrupt arrives while VMRUN is stalled, VMRUN can now
> terminate with the corresponding #VMEXIT intercept code, without
> entering guest mode, and thus without injecting the event.
> 
> For example, on a 2-way SMT core running vCPU0 on thread 0 and vCPU1 on
> thread 1:
>   Thread 0 (vCPU0)                         Thread 1 (vCPU1)
>   ----------------                         ----------------
>   Interrupt A injected to the guest             in host
>   VMRUN                                           |
>     |                                             |
>     v                                             |
>   Stall waiting for sibling                       |
>     |                                             |
>     |  host INTR arrives on thread 0              |
>     |  while it waits                             |
>     |                                             |
>     v                                             |
>   #VMEXIT                                         v
>   Interrupt B injected to the guest              idle
>   VMRUN

So how is KVM_RUN_FORCE_IMMEDIATE_EXIT supposed to work?