Subject: Re: [PATCH v5 67/69] KVM: arm64: nv: Enable ARMv8.4-NV support

From: Marc Zyngier <[email-masked]>
Date: Thu, 27 Jan 2022 11:48:05 +0000

On Tue, 18 Jan 2022 11:50:18 +0000,
Ganapatrao Kulkarni <[email-masked]> wrote:
> 
> 
> 
> On 30-11-2021 01:31 am, Marc Zyngier wrote:
> > As all the VNCR-capable system registers are nicely separated
> > from the rest of the crowd, let's set HCR_EL2.NV2 on and let
> > the ball rolling.
> > 
> > Signed-off-by: Marc Zyngier <[email-masked]>
> > ---
> >   arch/arm64/include/asm/kvm_arm.h     |  1 +
> >   arch/arm64/include/asm/kvm_emulate.h | 23 +++++++++++++----------
> >   arch/arm64/include/asm/sysreg.h      |  1 +
> >   arch/arm64/kvm/hyp/vhe/switch.c      | 14 +++++++++++++-
> >   4 files changed, 28 insertions(+), 11 deletions(-)
> > 
> > diff --git a/arch/arm64/include/asm/kvm_arm.h b/arch/arm64/include/asm/kvm_arm.h
> > index b603466803d2..18c35446249f 100644
> > --- a/arch/arm64/include/asm/kvm_arm.h
> > +++ b/arch/arm64/include/asm/kvm_arm.h
> > @@ -20,6 +20,7 @@
> >   #define HCR_AMVOFFEN	(UL(1) << 51)
> >   #define HCR_FIEN	(UL(1) << 47)
> >   #define HCR_FWB		(UL(1) << 46)
> > +#define HCR_NV2		(UL(1) << 45)
> >   #define HCR_AT		(UL(1) << 44)
> >   #define HCR_NV1		(UL(1) << 43)
> >   #define HCR_NV		(UL(1) << 42)
> > diff --git a/arch/arm64/include/asm/kvm_emulate.h b/arch/arm64/include/asm/kvm_emulate.h
> > index 1664430be698..f282997e4a4c 100644
> > --- a/arch/arm64/include/asm/kvm_emulate.h
> > +++ b/arch/arm64/include/asm/kvm_emulate.h
> > @@ -245,21 +245,24 @@ static inline bool is_hyp_ctxt(const struct kvm_vcpu *vcpu)
> >     static inline u64 __fixup_spsr_el2_write(struct kvm_cpu_context
> > *ctxt, u64 val)
> >   {
> > -	if (!__vcpu_el2_e2h_is_set(ctxt)) {
> > -		/*
> > -		 * Clear the .M field when writing SPSR to the CPU, so that we
> > -		 * can detect when the CPU clobbered our SPSR copy during a
> > -		 * local exception.
> > -		 */
> > -		val &= ~0xc;
> > -	}
> > +	struct kvm_vcpu *vcpu = container_of(ctxt, struct kvm_vcpu, arch.ctxt);
> > +
> > +	if (enhanced_nested_virt_in_use(vcpu) || __vcpu_el2_e2h_is_set(ctxt))
> > +		return val;
> >   -	return val;
> > +	/*
> > +	 * Clear the .M field when writing SPSR to the CPU, so that we
> > +	 * can detect when the CPU clobbered our SPSR copy during a
> > +	 * local exception.
> > +	 */
> > +	return val &= ~0xc;
> >   }
> >     static inline u64 __fixup_spsr_el2_read(const struct
> > kvm_cpu_context *ctxt, u64 val)
> >   {
> > -	if (__vcpu_el2_e2h_is_set(ctxt))
> > +	struct kvm_vcpu *vcpu = container_of(ctxt, struct kvm_vcpu, arch.ctxt);
> > +
> > +	if (enhanced_nested_virt_in_use(vcpu) || __vcpu_el2_e2h_is_set(ctxt))
> >   		return val;
> >     	/*
> > diff --git a/arch/arm64/include/asm/sysreg.h b/arch/arm64/include/asm/sysreg.h
> > index 71e6a0410e7c..5de90138d0a4 100644
> > --- a/arch/arm64/include/asm/sysreg.h
> > +++ b/arch/arm64/include/asm/sysreg.h
> > @@ -550,6 +550,7 @@
> >   #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_ZCR_EL2			sys_reg(3, 4, 1, 2, 0)
> >   #define SYS_TRFCR_EL2			sys_reg(3, 4, 1, 2, 1)
> > diff --git a/arch/arm64/kvm/hyp/vhe/switch.c b/arch/arm64/kvm/hyp/vhe/switch.c
> > index ef4488db6dc1..5cadda79089a 100644
> > --- a/arch/arm64/kvm/hyp/vhe/switch.c
> > +++ b/arch/arm64/kvm/hyp/vhe/switch.c
> > @@ -45,7 +45,13 @@ static void __activate_traps(struct kvm_vcpu *vcpu)
> >   			 * the EL1 virtual memory control register accesses
> >   			 * as well as the AT S1 operations.
> >   			 */
> > -			hcr |= HCR_TVM | HCR_TRVM | HCR_AT | HCR_TTLB | HCR_NV1;
> > +			if (enhanced_nested_virt_in_use(vcpu)) {
> > +				hcr &= ~HCR_TVM;
> 
> I think, we should clear TRVM also?
> 				hcr &= ~(HCR_TVM | HCR_TRVM);

Hmmm. But TRVM is never set the first place, is it? It is only here
that we augment the host HCR_EL2 with various trap configurations
depending on whether the host is NV2 capable or not, whether the
guest is VHE or not, and whether the guest as set of additional flags
of its own.

Given that, I don't think there is a need to clear this bit.

Thanks,
	M.

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

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