Re: [PATCH 04/13] KVM: arm64: nv: Configure HCR_EL2 for FEAT_NV2

[Marc Zyngier <maz@kernel.org>]

On Tue, 20 Feb 2024 15:16:00 +0000,
Joey Gouly <joey.gouly@arm.com> wrote:
> 
> Hi,
> 
> On Mon, Feb 19, 2024 at 09:20:05AM +0000, Marc Zyngier wrote:
> > Add the HCR_EL2 configuration for FEAT_NV2, adding the required
> > bits for running a guest hypervisor, and overall merging the
> > allowed bits provided by the guest.
> > 
> > This heavily replies on unavaliable features being sanitised
> > when the HCR_EL2 shadow register is accessed, and only a couple
> > of bits must be explicitly disabled.
> > 
> > Non-NV guests are completely unaffected by any of this.
> > 
> > Signed-off-by: Marc Zyngier <maz@kernel.org>
> > ---
> >  arch/arm64/include/asm/sysreg.h         |  1 +
> >  arch/arm64/kvm/hyp/include/hyp/switch.h |  4 +--
> >  arch/arm64/kvm/hyp/nvhe/switch.c        |  2 +-
> >  arch/arm64/kvm/hyp/vhe/switch.c         | 34 ++++++++++++++++++++++++-
> >  4 files changed, 36 insertions(+), 5 deletions(-)
> > 
> > diff --git a/arch/arm64/include/asm/sysreg.h b/arch/arm64/include/asm/sysreg.h
> > index 9e8999592f3a..a5361d9032a4 100644
> > --- a/arch/arm64/include/asm/sysreg.h
> > +++ b/arch/arm64/include/asm/sysreg.h
> > @@ -498,6 +498,7 @@
> >  #define SYS_TCR_EL2			sys_reg(3, 4, 2, 0, 2)
> >  #define SYS_VTTBR_EL2			sys_reg(3, 4, 2, 1, 0)
> >  #define SYS_VTCR_EL2			sys_reg(3, 4, 2, 1, 2)
> > +#define SYS_VNCR_EL2			sys_reg(3, 4, 2, 2, 0)
> >  
> >  #define SYS_TRFCR_EL2			sys_reg(3, 4, 1, 2, 1)
> >  #define SYS_VNCR_EL2			sys_reg(3, 4, 2, 2, 0)
> 
> I'm seeing double! (SYS_VNCR_EL2 is already defined a few lines
> down)

Ah, it got added by Miguel and my rebase didn't weed it out. It also
doesn't help that SYS_TRFCR_EL2 is out of sequence... Anyway, I'll
drop this, thanks for spotting it.

> 
> > diff --git a/arch/arm64/kvm/hyp/include/hyp/switch.h b/arch/arm64/kvm/hyp/include/hyp/switch.h
> > index e3fcf8c4d5b4..f5f701f309a9 100644
> > --- a/arch/arm64/kvm/hyp/include/hyp/switch.h
> > +++ b/arch/arm64/kvm/hyp/include/hyp/switch.h
> > @@ -271,10 +271,8 @@ static inline void __deactivate_traps_common(struct kvm_vcpu *vcpu)
> >  	__deactivate_traps_hfgxtr(vcpu);
> >  }
> >  
> > -static inline void ___activate_traps(struct kvm_vcpu *vcpu)
> > +static inline void ___activate_traps(struct kvm_vcpu *vcpu, u64 hcr)
> >  {
> > -	u64 hcr = vcpu->arch.hcr_el2;
> > -
> >  	if (cpus_have_final_cap(ARM64_WORKAROUND_CAVIUM_TX2_219_TVM))
> >  		hcr |= HCR_TVM;
> >  
> > diff --git a/arch/arm64/kvm/hyp/nvhe/switch.c b/arch/arm64/kvm/hyp/nvhe/switch.c
> > index c50f8459e4fc..4103625e46c5 100644
> > --- a/arch/arm64/kvm/hyp/nvhe/switch.c
> > +++ b/arch/arm64/kvm/hyp/nvhe/switch.c
> > @@ -40,7 +40,7 @@ static void __activate_traps(struct kvm_vcpu *vcpu)
> >  {
> >  	u64 val;
> >  
> > -	___activate_traps(vcpu);
> > +	___activate_traps(vcpu, vcpu->arch.hcr_el2);
> >  	__activate_traps_common(vcpu);
> >  
> >  	val = vcpu->arch.cptr_el2;
> > diff --git a/arch/arm64/kvm/hyp/vhe/switch.c b/arch/arm64/kvm/hyp/vhe/switch.c
> > index 58415783fd53..29f59c374f7a 100644
> > --- a/arch/arm64/kvm/hyp/vhe/switch.c
> > +++ b/arch/arm64/kvm/hyp/vhe/switch.c
> > @@ -33,11 +33,43 @@ DEFINE_PER_CPU(struct kvm_host_data, kvm_host_data);
> >  DEFINE_PER_CPU(struct kvm_cpu_context, kvm_hyp_ctxt);
> >  DEFINE_PER_CPU(unsigned long, kvm_hyp_vector);
> >  
> > +/*
> > + * HCR_EL2 bits that the NV guest can freely change (no RES0/RES1
> > + * semantics, irrespective of the configuration), but that cannot be
> > + * applied to the actual HW as things would otherwise break badly.
> > + *
> > + * - TGE: we want to use EL1, which is incompatible with it being set
> 
> Can you make this a bit clearer:
> 
> 	we want the guest to use EL1
> 
> Assuming I've understood correctly. I first read it as 'we' == kvm.

Sure thing, happy to update that.

>> > + *
> > + * - API/APK: for hysterical raisins, we enable PAuth lazily, which
> > + *   means that the guest's bits cannot be directly applied (we really
> > + *   want to see the traps). Revisit this at some point.
> > + */
> > +#define NV_HCR_GUEST_EXCLUDE	(HCR_TGE | HCR_API | HCR_APK)
> > +
> > +static u64 __compute_hcr(struct kvm_vcpu *vcpu)
> > +{
> > +	u64 hcr = vcpu->arch.hcr_el2;
> > +
> > +	if (!vcpu_has_nv(vcpu))
> > +		return hcr;
> > +
> > +	if (is_hyp_ctxt(vcpu)) {
> > +		hcr |= HCR_NV | HCR_NV2 | HCR_AT | HCR_TTLB;
> > +
> > +		if (!vcpu_el2_e2h_is_set(vcpu))
> > +			hcr |= HCR_NV1;
> > +
> > +		write_sysreg_s(vcpu->arch.ctxt.vncr_array, SYS_VNCR_EL2);
> > +	}
> > +
> > +	return hcr | (__vcpu_sys_reg(vcpu, HCR_EL2) & ~NV_HCR_GUEST_EXCLUDE);
> > +}
> > +
> >  static void __activate_traps(struct kvm_vcpu *vcpu)
> >  {
> >  	u64 val;
> >  
> > -	___activate_traps(vcpu);
> > +	___activate_traps(vcpu, __compute_hcr(vcpu));
> >  
> >  	if (has_cntpoff()) {
> >  		struct timer_map map;
> 
> Otherwise,
> 
> Reviewed-by: Joey Gouly <joey.gouly@arm.com>

Thanks!

	M.

-- 
Without deviation from the norm, progress is not possible.