Re: [PATCH] KVM: x86: preserve interrupt shadow across SMM entries

Paolo Bonzini
2022-06-07T15:23:50Z

On 6/7/22 17:16, Maxim Levitsky wrote:
> If the #SMI happens while the vCPU is in the interrupt shadow,
> (after STI or MOV SS),
> we must both clear it to avoid VM entry failure on VMX,
> due to consistency check vs EFLAGS.IF which is cleared on SMM entries,
> and restore it on RSM so that #SMI is transparent to the non SMM code.
>
> To support migration, reuse upper 4 bits of
> 'kvm_vcpu_events.interrupt.shadow' to store the smm interrupt shadow.
>
> This was lightly tested with a linux guest and smm load script,
> and a unit test will be soon developed to test this better.
>
> For discussion: there are other ways to fix this issue:
>
> 1. The SMM shadow can be stored in SMRAM at some unused
> offset, this will allow to avoid changes to kvm_vcpu_ioctl_x86_set_vcpu_events

Yes, that would be better (and would not require a new cap).

Paolo