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

From: Oliver Upton <[email-masked]>
Date: Mon, 1 Jun 2026 12:19:52 -0700

On Mon, Jun 01, 2026 at 08:17:18PM +0100, Fuad Tabba wrote:
> On Mon, 1 Jun 2026 at 20:16, Oliver Upton <[email-masked]> wrote:
> >
> > On Sun, May 31, 2026 at 04:45:48PM +0100, [email-masked] 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? :)

Marc is kindly dealing with the tree for the time being so hopefully
he can throw it in.

Thanks,
Oliver

> > > 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 <[email-masked]>
> >
> > Reviewed-by: Oliver Upton <[email-masked]>
> >
> > 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
> > >