[PATCH v2 20/36] KVM: arm64: Don't save the host ELR_EL2 and SPSR_EL2 on VHE systems

[Christoffer Dall]

On Mon, Dec 11, 2017 at 10:44:59AM +0000, Marc Zyngier wrote:
> On 07/12/17 17:06, Christoffer Dall wrote:
> > On non-VHE systems we need to save the ELR_EL2 and SPSR_EL2 so that we
> > can return to the host in EL1 in the same state and location where we
> > issued a hypercall to EL2, but these registers don't contain anything
> > important on VHE, because all of the host runs in EL2.  Therefore,
> 
> If I may refine the rational: ELR_EL2 and SPSR_EL2 are not useful here
> because we never enter a guest as a result of an exception entry that
> would be directly handled by KVM. The kernel entry code already saves
> ELR_EL1/SPSR_EL1 on exception entry, which is enough.
> 

Indeed, I was being a bit loosey-goosey here.

> > factor out these registers into separate save/restore functions, making
> > it easy to exclude them from the VHE world-switch path later on.
> > 
> > Signed-off-by: Christoffer Dall <christoffer.dall at linaro.org>
> > ---
> >  arch/arm64/kvm/hyp/sysreg-sr.c | 13 +++++++++++++
> >  1 file changed, 13 insertions(+)
> > 
> > diff --git a/arch/arm64/kvm/hyp/sysreg-sr.c b/arch/arm64/kvm/hyp/sysreg-sr.c
> > index a12112494f75..479de0f0dd07 100644
> > --- a/arch/arm64/kvm/hyp/sysreg-sr.c
> > +++ b/arch/arm64/kvm/hyp/sysreg-sr.c
> > @@ -71,6 +71,10 @@ static void __hyp_text __sysreg_save_el1_state(struct kvm_cpu_context *ctxt)
> >  	ctxt->gp_regs.sp_el1		= read_sysreg(sp_el1);
> >  	ctxt->gp_regs.elr_el1		= read_sysreg_el1(elr);
> >  	ctxt->gp_regs.spsr[KVM_SPSR_EL1]= read_sysreg_el1(spsr);
> > +}
> > +
> > +static void __hyp_text __sysreg_save_el2_return_state(struct kvm_cpu_context *ctxt)
> > +{
> >  	ctxt->gp_regs.regs.pc		= read_sysreg_el2(elr);
> >  	ctxt->gp_regs.regs.pstate	= read_sysreg_el2(spsr);
> >  }
> > @@ -80,6 +84,7 @@ void __hyp_text __sysreg_save_state_nvhe(struct kvm_cpu_context *ctxt)
> >  	__sysreg_save_el1_state(ctxt);
> >  	__sysreg_save_common_state(ctxt);
> >  	__sysreg_save_user_state(ctxt);
> > +	__sysreg_save_el2_return_state(ctxt);
> >  }
> >  
> >  void sysreg_save_host_state_vhe(struct kvm_cpu_context *ctxt)
> > @@ -93,6 +98,7 @@ void sysreg_save_guest_state_vhe(struct kvm_cpu_context *ctxt)
> >  	__sysreg_save_el1_state(ctxt);
> >  	__sysreg_save_common_state(ctxt);
> >  	__sysreg_save_user_state(ctxt);
> > +	__sysreg_save_el2_return_state(ctxt);
> >  }
> >  
> >  static void __hyp_text __sysreg_restore_common_state(struct kvm_cpu_context *ctxt)
> > @@ -137,6 +143,11 @@ static void __hyp_text __sysreg_restore_el1_state(struct kvm_cpu_context *ctxt)
> >  	write_sysreg(ctxt->gp_regs.sp_el1,		sp_el1);
> >  	write_sysreg_el1(ctxt->gp_regs.elr_el1,		elr);
> >  	write_sysreg_el1(ctxt->gp_regs.spsr[KVM_SPSR_EL1],spsr);
> > +}
> > +
> > +static void __hyp_text
> > +__sysreg_restore_el2_return_state(struct kvm_cpu_context *ctxt)
> > +{
> >  	write_sysreg_el2(ctxt->gp_regs.regs.pc,		elr);
> >  	write_sysreg_el2(ctxt->gp_regs.regs.pstate,	spsr);
> >  }
> > @@ -146,6 +157,7 @@ void __hyp_text __sysreg_restore_state_nvhe(struct kvm_cpu_context *ctxt)
> >  	__sysreg_restore_el1_state(ctxt);
> >  	__sysreg_restore_common_state(ctxt);
> >  	__sysreg_restore_user_state(ctxt);
> > +	__sysreg_restore_el2_return_state(ctxt);
> >  }
> >  
> >  void sysreg_restore_host_state_vhe(struct kvm_cpu_context *ctxt)
> > @@ -159,6 +171,7 @@ void sysreg_restore_guest_state_vhe(struct kvm_cpu_context *ctxt)
> >  	__sysreg_restore_el1_state(ctxt);
> >  	__sysreg_restore_common_state(ctxt);
> >  	__sysreg_restore_user_state(ctxt);
> > +	__sysreg_restore_el2_return_state(ctxt);
> >  }
> >  
> >  static void __hyp_text __fpsimd32_save_state(struct kvm_cpu_context *ctxt)
> > 
> 
> Otherwise:
> 
> Reviewed-by: Marc Zyngier <marc.zyngier at arm.com>
> 

Thanks,
-Christoffer