Re: [PATCH v4 33/40] KVM: arm64: Configure c15, PMU, and debug register traps on cpu load/put for VHE

From: Marc Zyngier <marc.zyngier@arm.com>
To: Christoffer Dall <christoffer.dall@linaro.org>
Cc: kvm@vger.kernel.org, kvmarm@lists.cs.columbia.edu,
	Yury Norov <ynorov@caviumnetworks.com>,
	linux-arm-kernel@lists.infradead.org,
	Dave Martin <Dave.Martin@arm.com>,
	Shih-Wei Li <shihwei@cs.columbia.edu>
Subject: Re: [PATCH v4 33/40] KVM: arm64: Configure c15, PMU, and debug register traps on cpu load/put for VHE
Date: Wed, 21 Feb 2018 18:20:54 +0000	[thread overview]
Message-ID: <86woz6jjax.wl-marc.zyngier@arm.com> (raw)
In-Reply-To: <20180215210332.8648-34-christoffer.dall@linaro.org>

On Thu, 15 Feb 2018 21:03:25 +0000,
Christoffer Dall wrote:
> 
> We do not have to change the c15 trap setting on each switch to/from the
> guest on VHE systems, because this setting only affects EL0.

Did you mean EL1 instead?

> 
> The PMU and debug trap configuration can also be done on vcpu load/put
> instead, because they don't affect how the host kernel can access the
> debug registers while executing KVM kernel code.
> 
> Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>
> ---
>  arch/arm64/include/asm/kvm_hyp.h |  3 +++
>  arch/arm64/kvm/hyp/switch.c      | 31 ++++++++++++++++++++++---------
>  arch/arm64/kvm/hyp/sysreg-sr.c   |  4 ++++
>  3 files changed, 29 insertions(+), 9 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/kvm_hyp.h b/arch/arm64/include/asm/kvm_hyp.h
> index 2b1fda90dde4..949f2e77ae58 100644
> --- a/arch/arm64/include/asm/kvm_hyp.h
> +++ b/arch/arm64/include/asm/kvm_hyp.h
> @@ -147,6 +147,9 @@ void __fpsimd_save_state(struct user_fpsimd_state *fp_regs);
>  void __fpsimd_restore_state(struct user_fpsimd_state *fp_regs);
>  bool __fpsimd_enabled(void);
>  
> +void activate_traps_vhe_load(struct kvm_vcpu *vcpu);
> +void deactivate_traps_vhe_put(void);
> +
>  u64 __guest_enter(struct kvm_vcpu *vcpu, struct kvm_cpu_context *host_ctxt);
>  void __noreturn __hyp_do_panic(unsigned long, ...);
>  
> diff --git a/arch/arm64/kvm/hyp/switch.c b/arch/arm64/kvm/hyp/switch.c
> index 9c40e203bd09..5e94955b89ea 100644
> --- a/arch/arm64/kvm/hyp/switch.c
> +++ b/arch/arm64/kvm/hyp/switch.c
> @@ -101,6 +101,8 @@ static void __hyp_text __activate_traps_nvhe(struct kvm_vcpu *vcpu)
>  {
>  	u64 val;
>  
> +	__activate_traps_common(vcpu);
> +
>  	val = CPTR_EL2_DEFAULT;
>  	val |= CPTR_EL2_TTA | CPTR_EL2_TFP | CPTR_EL2_TZ;
>  	write_sysreg(val, cptr_el2);
> @@ -120,20 +122,12 @@ static void __hyp_text __activate_traps(struct kvm_vcpu *vcpu)
>  		write_sysreg_s(vcpu->arch.vsesr_el2, SYS_VSESR_EL2);
>  
>  	__activate_traps_fpsimd32(vcpu);
> -	__activate_traps_common(vcpu);
>  	__activate_traps_arch()(vcpu);
>  }
>  
>  static void __hyp_text __deactivate_traps_vhe(void)
>  {
>  	extern char vectors[];	/* kernel exception vectors */
> -	u64 mdcr_el2 = read_sysreg(mdcr_el2);
> -
> -	mdcr_el2 &= MDCR_EL2_HPMN_MASK |
> -		    MDCR_EL2_E2PB_MASK << MDCR_EL2_E2PB_SHIFT |
> -		    MDCR_EL2_TPMS;
> -
> -	write_sysreg(mdcr_el2, mdcr_el2);
>  	write_sysreg(HCR_HOST_VHE_FLAGS, hcr_el2);
>  	write_sysreg(CPACR_EL1_DEFAULT, cpacr_el1);
>  	write_sysreg(vectors, vbar_el1);
> @@ -143,6 +137,8 @@ static void __hyp_text __deactivate_traps_nvhe(void)
>  {
>  	u64 mdcr_el2 = read_sysreg(mdcr_el2);
>  
> +	__deactivate_traps_common();
> +
>  	mdcr_el2 &= MDCR_EL2_HPMN_MASK;
>  	mdcr_el2 |= MDCR_EL2_E2PB_MASK << MDCR_EL2_E2PB_SHIFT;
>  
> @@ -166,10 +162,27 @@ static void __hyp_text __deactivate_traps(struct kvm_vcpu *vcpu)
>  	if (vcpu->arch.hcr_el2 & HCR_VSE)
>  		vcpu->arch.hcr_el2 = read_sysreg(hcr_el2);
>  
> -	__deactivate_traps_common();
>  	__deactivate_traps_arch()();
>  }
>  
> +void activate_traps_vhe_load(struct kvm_vcpu *vcpu)
> +{
> +	__activate_traps_common(vcpu);
> +}
> +
> +void deactivate_traps_vhe_put(void)
> +{
> +	u64 mdcr_el2 = read_sysreg(mdcr_el2);
> +
> +	mdcr_el2 &= MDCR_EL2_HPMN_MASK |
> +		    MDCR_EL2_E2PB_MASK << MDCR_EL2_E2PB_SHIFT |
> +		    MDCR_EL2_TPMS;
> +
> +	write_sysreg(mdcr_el2, mdcr_el2);
> +
> +	__deactivate_traps_common();
> +}
> +
>  static void __hyp_text __activate_vm(struct kvm *kvm)
>  {
>  	write_sysreg(kvm->arch.vttbr, vttbr_el2);
> diff --git a/arch/arm64/kvm/hyp/sysreg-sr.c b/arch/arm64/kvm/hyp/sysreg-sr.c
> index aacba4636871..b3894df6bf1a 100644
> --- a/arch/arm64/kvm/hyp/sysreg-sr.c
> +++ b/arch/arm64/kvm/hyp/sysreg-sr.c
> @@ -254,6 +254,8 @@ void kvm_vcpu_load_sysregs(struct kvm_vcpu *vcpu)
>  	__sysreg_restore_el1_state(guest_ctxt);
>  
>  	vcpu->arch.sysregs_loaded_on_cpu = true;
> +
> +	activate_traps_vhe_load(vcpu);
>  }
>  
>  /**
> @@ -275,6 +277,8 @@ void kvm_vcpu_put_sysregs(struct kvm_vcpu *vcpu)
>  	if (!has_vhe())
>  		return;
>  
> +	deactivate_traps_vhe_put();
> +
>  	__sysreg_save_el1_state(guest_ctxt);
>  	__sysreg_save_user_state(guest_ctxt);
>  	__sysreg32_save_state(vcpu);
> -- 
> 2.14.2
> 

I must admit that I find these two layers of trap configuration mildly
confusing. I can see why it is done like this (there is hardly any
other way), but still...

Reviewed-by: Marc Zyngier <marc.zyngier@arm.com>

	M.

-- 
Jazz is not dead, it just smell funny.