Re: [PATCH 5/6] KVM: nVMX: Always use IBPB to properly virtualize IBRS

[Sean Christopherson]

On Wed, Feb 19, 2025, Yosry Ahmed wrote:
> On synthesized nested VM-exits in VMX, an IBPB is performed if IBRS is
> advertised to the guest to properly provide separate prediction domains
> for L1 and L2. However, this is currently conditional on
> X86_FEATURE_USE_IBPB, which depends on the host spectre_v2_user
> mitigation.
> 
> In short, if spectre_v2_user=no, IBRS is not virtualized correctly and
> L1 becomes suspectible to attacks from L2. Fix this by performing the
> IBPB regardless of X86_FEATURE_USE_IBPB.
> 
> Fixes: 2e7eab81425a ("KVM: VMX: Execute IBPB on emulated VM-exit when guest has IBRS")
> Signed-off-by: Yosry Ahmed <yosry.ahmed@xxxxxxxxx>
> ---

Acked-by: Sean Christopherson <seanjc@xxxxxxxxxx>