[PATCH v1 05/11] KVM: arm64: Make vcpu_{read,write}_sys_reg available to HYP code

[Fuad Tabba]

On Mon, 15 Jun 2026 at 14:11, Vincent Donnefort <vdonnefort at google.com> wrote:
>
> On Fri, Jun 12, 2026 at 07:59:19AM +0100, tabba at google.com wrote:
> > The vcpu_{read,write}_sys_reg() accessors are host-only, so helpers
> > built on them such as kvm_vcpu_set_be()/kvm_vcpu_is_be() cannot be
> > shared with hyp code. Add _vcpu_read_sys_reg()/_vcpu_write_sys_reg()
> > inlines in kvm_emulate.h that dispatch on is_nvhe_hyp_code() to the
> > host- or hyp-side accessor. A follow-up series uses this to share that
> > emulation code at EL2.
> >
> > No functional change intended.
> >
> > Signed-off-by: Fuad Tabba <tabba at google.com>
> > ---
> >  arch/arm64/include/asm/kvm_emulate.h | 22 +++++++++++++++++++---
> >  1 file changed, 19 insertions(+), 3 deletions(-)
> >
> > diff --git a/arch/arm64/include/asm/kvm_emulate.h b/arch/arm64/include/asm/kvm_emulate.h
> > index 5bf3d7e1d92c..aed9fc0b717b 100644
> > --- a/arch/arm64/include/asm/kvm_emulate.h
> > +++ b/arch/arm64/include/asm/kvm_emulate.h
> > @@ -506,6 +506,22 @@ static inline unsigned long kvm_vcpu_get_mpidr_aff(struct kvm_vcpu *vcpu)
> >       return __vcpu_sys_reg(vcpu, MPIDR_EL1) & MPIDR_HWID_BITMASK;
> >  }
> >
> > +static inline u64 _vcpu_read_sys_reg(struct kvm_vcpu *vcpu, enum vcpu_sysreg reg)
>
> I am not sure a single underscore is widely used in the kernel.
>
> Why not move __vcpu_read_sys_reg() and __vcpu_write_sys_reg() from exception.c
> to kvm_emulate.h? especially this already checks has_vhe().

Good point. has_vhe() already returns a compile-time constant
in hyp code and a runtime cap check at EL1, so it works in all
contexts. I'll move them to kvm_emulate.h and rename to
kvm_vcpu_read_sys_reg() / kvm_vcpu_write_sys_reg().

Cheers,
/fuad

>
> > +{
> > +     if (!is_nvhe_hyp_code())
> > +             return vcpu_read_sys_reg(vcpu, reg);
> > +
> > +     return __vcpu_sys_reg(vcpu, reg);
> > +}
> > +
> > +static inline void _vcpu_write_sys_reg(struct kvm_vcpu *vcpu, u64 val, enum vcpu_sysreg reg)
> > +{
> > +     if (!is_nvhe_hyp_code())
> > +             vcpu_write_sys_reg(vcpu, val, reg);
> > +     else
> > +             __vcpu_assign_sys_reg(vcpu, reg, val);
> > +}
> > +
> >  static inline void kvm_vcpu_set_be(struct kvm_vcpu *vcpu)
> >  {
> >       if (vcpu_mode_is_32bit(vcpu)) {
> > @@ -516,9 +532,9 @@ static inline void kvm_vcpu_set_be(struct kvm_vcpu *vcpu)
> >
> >               r = vcpu_has_nv(vcpu) ? SCTLR_EL2 : SCTLR_EL1;
> >
> > -             sctlr = vcpu_read_sys_reg(vcpu, r);
> > +             sctlr = _vcpu_read_sys_reg(vcpu, r);
> >               sctlr |= SCTLR_ELx_EE;
> > -             vcpu_write_sys_reg(vcpu, sctlr, r);
> > +             _vcpu_write_sys_reg(vcpu, sctlr, r);
> >       }
> >  }
> >
> > @@ -533,7 +549,7 @@ static inline bool kvm_vcpu_is_be(struct kvm_vcpu *vcpu)
> >       r = is_hyp_ctxt(vcpu) ? SCTLR_EL2 : SCTLR_EL1;
> >       bit = vcpu_mode_priv(vcpu) ? SCTLR_ELx_EE : SCTLR_EL1_E0E;
> >
> > -     return vcpu_read_sys_reg(vcpu, r) & bit;
> > +     return _vcpu_read_sys_reg(vcpu, r) & bit;
> >  }
> >
> >  static inline unsigned long vcpu_data_guest_to_host(struct kvm_vcpu *vcpu,
> > --
> > 2.54.0.1136.gdb2ca164c4-goog
> >