On Tue, Sep 01, 2026 at 10:47:02PM +0100, Mark Brown wrote: > In order to allow efficient implementation of GCS implementations are > permitted to do GCS specific caching, with barriers implicit in stack > switch operations and GCSB DSYNC as an explicit barrier. Since we do > not use GCS in the hypervisor or host kernel the hypervisor cannot rely > on any barriers being present in vCPU context switches other than those > it explicitly inserts. Add explicit barriers when loading and saving > vCPU state. > > Signed-off-by: Mark Brown <[email protected]>
LGTM so: Reviewed-by: Lorenzo Stoakes (ARM) <[email protected]> > Reviewed-by: Yuan Yao <[email protected]> > --- > arch/arm64/kvm/arm.c | 7 +++++++ > arch/arm64/kvm/hyp/nvhe/hyp-main.c | 7 +++++++ > 2 files changed, 14 insertions(+) > > diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c > index 8b080804bc90..52f53f682e6a 100644 > --- a/arch/arm64/kvm/arm.c > +++ b/arch/arm64/kvm/arm.c > @@ -755,6 +755,13 @@ void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu) So this seems to be where -> vCPU unscheduled so the right place to do it. > vcpu_set_flag(vcpu, PKVM_HOST_STATE_DIRTY); > } > > + /* > + * Ensure any GCS memory effects from the outgoing vCPU are > + * visible elsewhere. > + */ > + if (kvm_has_gcs(vcpu->kvm)) > + gcsb_dsync(); Makes sense. I did notice the curious: static inline void gcsb_dsync(void) { asm volatile(".inst 0xd503227f" : : : "memory"); } And various sludging around suggests this is HINT #19 and guaranteed to be a nop on arches that don't implement the feature :) > + > kvm_vcpu_put_debug(vcpu); > kvm_arch_vcpu_put_fp(vcpu); > if (has_vhe()) > diff --git a/arch/arm64/kvm/hyp/nvhe/hyp-main.c > b/arch/arm64/kvm/hyp/nvhe/hyp-main.c > index 9a3b92e626ad..534db037c5f6 100644 > --- a/arch/arm64/kvm/hyp/nvhe/hyp-main.c > +++ b/arch/arm64/kvm/hyp/nvhe/hyp-main.c > @@ -261,6 +261,13 @@ static void sync_hyp_vcpu(struct pkvm_hyp_vcpu *hyp_vcpu) And here similar for pKVM. > fpsimd_sve_sync(&hyp_vcpu->vcpu); > sync_debug_state(hyp_vcpu); > > + /* > + * Ensure any GCS memory effects from the outgoing vCPU are > + * visible elsewhere even if the host skips syncing. > + */ > + if (kvm_has_gcs(hyp_vcpu->vcpu.kvm)) > + gcsb_dsync(); > + > if (pkvm_hyp_vcpu_is_protected(hyp_vcpu)) { > host_vcpu->arch.ctxt = hyp_vcpu->vcpu.arch.ctxt; > } else { > > -- > 2.47.3 > > -- Cheers, Lorenzo
