linux-kernel - Re: [PATCH v2 09/18] arm64: KVM: enable conditional save/restore full SPE profiling buffer controls

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Message-ID: <20191220180657.GD25258@lakrids.cambridge.arm.com>
Date:   Fri, 20 Dec 2019 18:06:58 +0000
From:   Mark Rutland <mark.rutland@....com>
To:     Andrew Murray <andrew.murray@....com>
Cc:     Marc Zyngier <marc.zyngier@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Sudeep Holla <sudeep.holla@....com>,
        kvmarm@...ts.cs.columbia.edu, linux-arm-kernel@...ts.infradead.org,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 09/18] arm64: KVM: enable conditional save/restore
 full SPE profiling buffer controls

On Fri, Dec 20, 2019 at 02:30:16PM +0000, Andrew Murray wrote:
> From: Sudeep Holla <sudeep.holla@....com>
> 
> Now that we can save/restore the full SPE controls, we can enable it
> if SPE is setup and ready to use in KVM. It's supported in KVM only if
> all the CPUs in the system supports SPE.
> 
> However to support heterogenous systems, we need to move the check if
> host supports SPE and do a partial save/restore.

I don't think that it makes sense to support this for heterogeneous
systems, given their SPE capabilities and IMP DEF details will differ.

Is there some way we can limit this to homogeneous systems?

Thanks,
Mark.

> 
> Signed-off-by: Sudeep Holla <sudeep.holla@....com>
> Signed-off-by: Andrew Murray <andrew.murray@....com>
> ---
>  arch/arm64/kvm/hyp/debug-sr.c | 33 ++++++++++++++++-----------------
>  include/kvm/arm_spe.h         |  6 ++++++
>  2 files changed, 22 insertions(+), 17 deletions(-)
> 
> diff --git a/arch/arm64/kvm/hyp/debug-sr.c b/arch/arm64/kvm/hyp/debug-sr.c
> index 12429b212a3a..d8d857067e6d 100644
> --- a/arch/arm64/kvm/hyp/debug-sr.c
> +++ b/arch/arm64/kvm/hyp/debug-sr.c
> @@ -86,18 +86,13 @@
>  	}
>  
>  static void __hyp_text
> -__debug_save_spe_nvhe(struct kvm_cpu_context *ctxt, bool full_ctxt)
> +__debug_save_spe_context(struct kvm_cpu_context *ctxt, bool full_ctxt)
>  {
>  	u64 reg;
>  
>  	/* Clear pmscr in case of early return */
>  	ctxt->sys_regs[PMSCR_EL1] = 0;
>  
> -	/* SPE present on this CPU? */
> -	if (!cpuid_feature_extract_unsigned_field(read_sysreg(id_aa64dfr0_el1),
> -						  ID_AA64DFR0_PMSVER_SHIFT))
> -		return;
> -
>  	/* Yes; is it owned by higher EL? */
>  	reg = read_sysreg_s(SYS_PMBIDR_EL1);
>  	if (reg & BIT(SYS_PMBIDR_EL1_P_SHIFT))
> @@ -142,7 +137,7 @@ __debug_save_spe_nvhe(struct kvm_cpu_context *ctxt, bool full_ctxt)
>  }
>  
>  static void __hyp_text
> -__debug_restore_spe_nvhe(struct kvm_cpu_context *ctxt, bool full_ctxt)
> +__debug_restore_spe_context(struct kvm_cpu_context *ctxt, bool full_ctxt)
>  {
>  	if (!ctxt->sys_regs[PMSCR_EL1])
>  		return;
> @@ -210,11 +205,14 @@ void __hyp_text __debug_restore_guest_context(struct kvm_vcpu *vcpu)
>  	struct kvm_guest_debug_arch *host_dbg;
>  	struct kvm_guest_debug_arch *guest_dbg;
>  
> +	host_ctxt = kern_hyp_va(vcpu->arch.host_cpu_context);
> +	guest_ctxt = &vcpu->arch.ctxt;
> +
> +	__debug_restore_spe_context(guest_ctxt, kvm_arm_spe_v1_ready(vcpu));
> +
>  	if (!(vcpu->arch.flags & KVM_ARM64_DEBUG_DIRTY))
>  		return;
>  
> -	host_ctxt = kern_hyp_va(vcpu->arch.host_cpu_context);
> -	guest_ctxt = &vcpu->arch.ctxt;
>  	host_dbg = &vcpu->arch.host_debug_state.regs;
>  	guest_dbg = kern_hyp_va(vcpu->arch.debug_ptr);
>  
> @@ -232,8 +230,7 @@ void __hyp_text __debug_restore_host_context(struct kvm_vcpu *vcpu)
>  	host_ctxt = kern_hyp_va(vcpu->arch.host_cpu_context);
>  	guest_ctxt = &vcpu->arch.ctxt;
>  
> -	if (!has_vhe())
> -		__debug_restore_spe_nvhe(host_ctxt, false);
> +	__debug_restore_spe_context(host_ctxt, kvm_arm_spe_v1_ready(vcpu));
>  
>  	if (!(vcpu->arch.flags & KVM_ARM64_DEBUG_DIRTY))
>  		return;
> @@ -249,19 +246,21 @@ void __hyp_text __debug_restore_host_context(struct kvm_vcpu *vcpu)
>  
>  void __hyp_text __debug_save_host_context(struct kvm_vcpu *vcpu)
>  {
> -	/*
> -	 * Non-VHE: Disable and flush SPE data generation
> -	 * VHE: The vcpu can run, but it can't hide.
> -	 */
>  	struct kvm_cpu_context *host_ctxt;
>  
>  	host_ctxt = kern_hyp_va(vcpu->arch.host_cpu_context);
> -	if (!has_vhe())
> -		__debug_save_spe_nvhe(host_ctxt, false);
> +	if (cpuid_feature_extract_unsigned_field(read_sysreg(id_aa64dfr0_el1),
> +						 ID_AA64DFR0_PMSVER_SHIFT))
> +		__debug_save_spe_context(host_ctxt, kvm_arm_spe_v1_ready(vcpu));
>  }
>  
>  void __hyp_text __debug_save_guest_context(struct kvm_vcpu *vcpu)
>  {
> +	bool kvm_spe_ready = kvm_arm_spe_v1_ready(vcpu);
> +
> +	/* SPE present on this vCPU? */
> +	if (kvm_spe_ready)
> +		__debug_save_spe_context(&vcpu->arch.ctxt, kvm_spe_ready);
>  }
>  
>  u32 __hyp_text __kvm_get_mdcr_el2(void)
> diff --git a/include/kvm/arm_spe.h b/include/kvm/arm_spe.h
> index 48d118fdb174..30c40b1bc385 100644
> --- a/include/kvm/arm_spe.h
> +++ b/include/kvm/arm_spe.h
> @@ -16,4 +16,10 @@ struct kvm_spe {
>  	bool irq_level;
>  };
>  
> +#ifdef CONFIG_KVM_ARM_SPE
> +#define kvm_arm_spe_v1_ready(v)		((v)->arch.spe.ready)
> +#else
> +#define kvm_arm_spe_v1_ready(v)		(false)
> +#endif /* CONFIG_KVM_ARM_SPE */
> +
>  #endif /* __ASM_ARM_KVM_SPE_H */
> -- 
> 2.21.0
>