[PATCH] KVM: arm64: Flush HCR_EL2.VSE to deliver SErrors to pKVM guests

[Fuad Tabba]

On Mon, 1 Jun 2026 at 20:16, Oliver Upton <oupton at kernel.org> wrote:
>
> On Sun, May 31, 2026 at 04:45:48PM +0100, tabba at google.com wrote:
> > With pKVM enabled, the host injects a virtual SError by setting
> > HCR_EL2.VSE on its vCPU copy, but flush_hyp_vcpu() only flows TWI/TWE
> > into the hyp vCPU that runs, so VSE never reaches it and a deferred
> > (masked) SError is never delivered. VSE is a host-owned injection
> > control, not a trap-configuration bit, so restricting the host's
> > trap-register values should not have dropped it. Flow it on entry;
> > sync_hyp_vcpu() already copies hcr_el2 back, so delivery is reflected
> > to the host.
>
> Might be worth mentioning that flush_hyp_vcpu() also forwards VSESR_EL2
> from the host since that bit is _just_ out of context of this diff :)

Sure, would you like me to respin? Or would one of the maintainers
kindly add that? :)

Cheers,
/fuad

> > Fixes: b56680de9c648 ("KVM: arm64: Initialize trap register values in hyp in pKVM")
> > Reported-by: Sashiko (local):gemini-3.1-pro
> > Signed-off-by: Fuad Tabba <tabba at google.com>
>
> Reviewed-by: Oliver Upton <oupton at kernel.org>
>
> Thanks,
> Oliver
>
> > ---
> > Not an urgent fix. I should stop running Sashiko...
> > ---
> >  arch/arm64/kvm/hyp/nvhe/hyp-main.c | 9 +++++++--
> >  1 file changed, 7 insertions(+), 2 deletions(-)
> >
> > diff --git a/arch/arm64/kvm/hyp/nvhe/hyp-main.c b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
> > index 06db299c37a8..9e4a20df6409 100644
> > --- a/arch/arm64/kvm/hyp/nvhe/hyp-main.c
> > +++ b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
> > @@ -129,9 +129,14 @@ static void flush_hyp_vcpu(struct pkvm_hyp_vcpu *hyp_vcpu)
> >       hyp_vcpu->vcpu.arch.ctxt        = host_vcpu->arch.ctxt;
> >
> >       hyp_vcpu->vcpu.arch.mdcr_el2    = host_vcpu->arch.mdcr_el2;
> > -     hyp_vcpu->vcpu.arch.hcr_el2 &= ~(HCR_TWI | HCR_TWE);
> > +     /*
> > +      * HCR_EL2.VSE is host-owned (a pending virtual SError to inject), not a
> > +      * trap-control bit, so it must flow to the hyp vCPU alongside TWI/TWE
> > +      * for the vSError to be delivered. sync_hyp_vcpu() reflects it back.
> > +      */
> > +     hyp_vcpu->vcpu.arch.hcr_el2 &= ~(HCR_TWI | HCR_TWE | HCR_VSE);
> >       hyp_vcpu->vcpu.arch.hcr_el2 |= READ_ONCE(host_vcpu->arch.hcr_el2) &
> > -                                              (HCR_TWI | HCR_TWE);
> > +                                              (HCR_TWI | HCR_TWE | HCR_VSE);
> >
> >       hyp_vcpu->vcpu.arch.iflags      = host_vcpu->arch.iflags;
> >
> > --
> > 2.54.0.929.g9b7fa37559-goog
> >