Date:   Fri, 5 Apr 2019 12:02:37 +0100
From:   Dave Martin <Dave.Martin@....com>
To:     Amit Daniel Kachhap <amit.kachhap@....com>
Cc:     linux-arm-kernel@...ts.infradead.org,
        Marc Zyngier <marc.zyngier@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Kristina Martsenko <kristina.martsenko@....com>,
        kvmarm@...ts.cs.columbia.edu,
        Ramana Radhakrishnan <ramana.radhakrishnan@....com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v8 5/9] KVM: arm/arm64: preserve host MDCR_EL2 value

On Tue, Apr 02, 2019 at 07:57:13AM +0530, Amit Daniel Kachhap wrote:
> Save host MDCR_EL2 value during kvm HYP initialisation and restore
> after every switch from host to guest. There should not be any
> change in functionality due to this.
> 
> The value of mdcr_el2 is now stored in struct kvm_cpu_context as
> both host and guest can now use this field in a common way.
> 
> Signed-off-by: Amit Daniel Kachhap <amit.kachhap@....com>
> Acked-by: Mark Rutland <mark.rutland@....com>
> Cc: Marc Zyngier <marc.zyngier@....com>
> Cc: Mark Rutland <mark.rutland@....com>
> Cc: Christoffer Dall <christoffer.dall@....com>
> Cc: kvmarm@...ts.cs.columbia.edu
> ---
> 
> Changes since v7:
> * Removed unused function __kvm_get_mdcr_el2 [Kristina].
> 
>  arch/arm/include/asm/kvm_host.h   |  1 -
>  arch/arm64/include/asm/kvm_asm.h  |  2 --
>  arch/arm64/include/asm/kvm_host.h |  6 ++----
>  arch/arm64/include/asm/kvm_hyp.h  |  2 +-
>  arch/arm64/kvm/debug.c            | 28 ++++++----------------------
>  arch/arm64/kvm/hyp/debug-sr.c     |  5 -----
>  arch/arm64/kvm/hyp/switch.c       | 18 +++++-------------
>  arch/arm64/kvm/hyp/sysreg-sr.c    |  8 +++++++-
>  virt/kvm/arm/arm.c                |  1 -
>  9 files changed, 21 insertions(+), 50 deletions(-)
> 
> diff --git a/arch/arm/include/asm/kvm_host.h b/arch/arm/include/asm/kvm_host.h
> index 6d0aac4..a928565 100644
> --- a/arch/arm/include/asm/kvm_host.h
> +++ b/arch/arm/include/asm/kvm_host.h
> @@ -343,7 +343,6 @@ static inline void kvm_arch_vcpu_uninit(struct kvm_vcpu *vcpu) {}
>  static inline void kvm_arch_sched_in(struct kvm_vcpu *vcpu, int cpu) {}
>  static inline void kvm_arch_vcpu_block_finish(struct kvm_vcpu *vcpu) {}
>  
> -static inline void kvm_arm_init_debug(void) {}
>  static inline void kvm_arm_setup_debug(struct kvm_vcpu *vcpu) {}
>  static inline void kvm_arm_clear_debug(struct kvm_vcpu *vcpu) {}
>  static inline void kvm_arm_reset_debug_ptr(struct kvm_vcpu *vcpu) {}
> diff --git a/arch/arm64/include/asm/kvm_asm.h b/arch/arm64/include/asm/kvm_asm.h
> index a68205c..a15ba55 100644
> --- a/arch/arm64/include/asm/kvm_asm.h
> +++ b/arch/arm64/include/asm/kvm_asm.h
> @@ -78,8 +78,6 @@ extern u64 __vgic_v3_read_vmcr(void);
>  extern void __vgic_v3_write_vmcr(u32 vmcr);
>  extern void __vgic_v3_init_lrs(void);
>  
> -extern u32 __kvm_get_mdcr_el2(void);
> -
>  extern void __kvm_populate_host_regs(void);
>  
>  /*
> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index 3b09fd0..e3ccd7b 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -211,6 +211,8 @@ struct kvm_cpu_context {
>  
>  	/* HYP host/guest configuration */
>  	u64 hcr_el2;
> +	u32 mdcr_el2;
> +
>  	struct kvm_vcpu *__hyp_running_vcpu;
>  };
>  
> @@ -226,9 +228,6 @@ struct vcpu_reset_state {
>  struct kvm_vcpu_arch {
>  	struct kvm_cpu_context ctxt;
>  
> -	/* HYP configuration */
> -	u32 mdcr_el2;
> -
>  	/* Exception Information */
>  	struct kvm_vcpu_fault_info fault;
>  
> @@ -498,7 +497,6 @@ static inline void kvm_arch_vcpu_uninit(struct kvm_vcpu *vcpu) {}
>  static inline void kvm_arch_sched_in(struct kvm_vcpu *vcpu, int cpu) {}
>  static inline void kvm_arch_vcpu_block_finish(struct kvm_vcpu *vcpu) {}
>  
> -void kvm_arm_init_debug(void);
>  void kvm_arm_setup_debug(struct kvm_vcpu *vcpu);
>  void kvm_arm_clear_debug(struct kvm_vcpu *vcpu);
>  void kvm_arm_reset_debug_ptr(struct kvm_vcpu *vcpu);
> diff --git a/arch/arm64/include/asm/kvm_hyp.h b/arch/arm64/include/asm/kvm_hyp.h
> index 4da765f..7fcde8a 100644
> --- a/arch/arm64/include/asm/kvm_hyp.h
> +++ b/arch/arm64/include/asm/kvm_hyp.h
> @@ -152,7 +152,7 @@ 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);
> +void deactivate_traps_vhe_put(struct kvm_vcpu *vcpu);
>  
>  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/debug.c b/arch/arm64/kvm/debug.c
> index fd917d6..99dc0a4 100644
> --- a/arch/arm64/kvm/debug.c
> +++ b/arch/arm64/kvm/debug.c
> @@ -32,8 +32,6 @@
>  				DBG_MDSCR_KDE | \
>  				DBG_MDSCR_MDE)
>  
> -static DEFINE_PER_CPU(u32, mdcr_el2);
> -
>  /**
>   * save/restore_guest_debug_regs
>   *
> @@ -65,21 +63,6 @@ static void restore_guest_debug_regs(struct kvm_vcpu *vcpu)
>  }
>  
>  /**
> - * kvm_arm_init_debug - grab what we need for debug
> - *
> - * Currently the sole task of this function is to retrieve the initial
> - * value of mdcr_el2 so we can preserve MDCR_EL2.HPMN which has
> - * presumably been set-up by some knowledgeable bootcode.
> - *
> - * It is called once per-cpu during CPU hyp initialisation.
> - */
> -
> -void kvm_arm_init_debug(void)
> -{
> -	__this_cpu_write(mdcr_el2, kvm_call_hyp_ret(__kvm_get_mdcr_el2));
> -}
> -
> -/**
>   * kvm_arm_reset_debug_ptr - reset the debug ptr to point to the vcpu state
>   */
>  
> @@ -111,6 +94,7 @@ void kvm_arm_reset_debug_ptr(struct kvm_vcpu *vcpu)
>  
>  void kvm_arm_setup_debug(struct kvm_vcpu *vcpu)
>  {
> +	kvm_cpu_context_t *host_cxt = this_cpu_ptr(&kvm_host_cpu_state);
>  	bool trap_debug = !(vcpu->arch.flags & KVM_ARM64_DEBUG_DIRTY);
>  	unsigned long mdscr;
>  
> @@ -120,8 +104,8 @@ void kvm_arm_setup_debug(struct kvm_vcpu *vcpu)
>  	 * This also clears MDCR_EL2_E2PB_MASK to disable guest access
>  	 * to the profiling buffer.
>  	 */
> -	vcpu->arch.mdcr_el2 = __this_cpu_read(mdcr_el2) & MDCR_EL2_HPMN_MASK;
> -	vcpu->arch.mdcr_el2 |= (MDCR_EL2_TPM |
> +	vcpu->arch.ctxt.mdcr_el2 = host_cxt->mdcr_el2 & MDCR_EL2_HPMN_MASK;
> +	vcpu->arch.ctxt.mdcr_el2 |= (MDCR_EL2_TPM |
>  				MDCR_EL2_TPMS |
>  				MDCR_EL2_TPMCR |
>  				MDCR_EL2_TDRA |
> @@ -130,7 +114,7 @@ void kvm_arm_setup_debug(struct kvm_vcpu *vcpu)
>  	/* Is Guest debugging in effect? */
>  	if (vcpu->guest_debug) {
>  		/* Route all software debug exceptions to EL2 */
> -		vcpu->arch.mdcr_el2 |= MDCR_EL2_TDE;
> +		vcpu->arch.ctxt.mdcr_el2 |= MDCR_EL2_TDE;
>  
>  		/* Save guest debug state */
>  		save_guest_debug_regs(vcpu);
> @@ -202,13 +186,13 @@ void kvm_arm_setup_debug(struct kvm_vcpu *vcpu)
>  
>  	/* Trap debug register access */
>  	if (trap_debug)
> -		vcpu->arch.mdcr_el2 |= MDCR_EL2_TDA;
> +		vcpu->arch.ctxt.mdcr_el2 |= MDCR_EL2_TDA;
>  
>  	/* If KDE or MDE are set, perform a full save/restore cycle. */
>  	if (vcpu_read_sys_reg(vcpu, MDSCR_EL1) & (DBG_MDSCR_KDE | DBG_MDSCR_MDE))
>  		vcpu->arch.flags |= KVM_ARM64_DEBUG_DIRTY;
>  
> -	trace_kvm_arm_set_dreg32("MDCR_EL2", vcpu->arch.mdcr_el2);
> +	trace_kvm_arm_set_dreg32("MDCR_EL2", vcpu->arch.ctxt.mdcr_el2);
>  	trace_kvm_arm_set_dreg32("MDSCR_EL1", vcpu_read_sys_reg(vcpu, MDSCR_EL1));
>  }
>  
> diff --git a/arch/arm64/kvm/hyp/debug-sr.c b/arch/arm64/kvm/hyp/debug-sr.c
> index 5000976..f49a3f7 100644
> --- a/arch/arm64/kvm/hyp/debug-sr.c
> +++ b/arch/arm64/kvm/hyp/debug-sr.c
> @@ -198,8 +198,3 @@ void __hyp_text __debug_switch_to_host(struct kvm_vcpu *vcpu)
>  
>  	vcpu->arch.flags &= ~KVM_ARM64_DEBUG_DIRTY;
>  }
> -
> -u32 __hyp_text __kvm_get_mdcr_el2(void)
> -{
> -	return read_sysreg(mdcr_el2);
> -}
> diff --git a/arch/arm64/kvm/hyp/switch.c b/arch/arm64/kvm/hyp/switch.c
> index f5cefa1..fe76e24 100644
> --- a/arch/arm64/kvm/hyp/switch.c
> +++ b/arch/arm64/kvm/hyp/switch.c
> @@ -84,7 +84,7 @@ static void __hyp_text __activate_traps_common(struct kvm_vcpu *vcpu)
>  	 */
>  	write_sysreg(0, pmselr_el0);
>  	write_sysreg(ARMV8_PMU_USERENR_MASK, pmuserenr_el0);
> -	write_sysreg(vcpu->arch.mdcr_el2, mdcr_el2);
> +	write_sysreg(vcpu->arch.ctxt.mdcr_el2, mdcr_el2);
>  }
>  
>  static void __hyp_text __deactivate_traps_common(void)
> @@ -161,15 +161,11 @@ NOKPROBE_SYMBOL(deactivate_traps_vhe);
>  
>  static void __hyp_text __deactivate_traps_nvhe(struct kvm_cpu_context *host_ctxt)
>  {
> -	u64 mdcr_el2 = read_sysreg(mdcr_el2);
>  	struct kvm_cpu_context *hyp_host_ctxt = kern_hyp_va(host_ctxt);
>  
>  	__deactivate_traps_common();
>  
> -	mdcr_el2 &= MDCR_EL2_HPMN_MASK;
> -	mdcr_el2 |= MDCR_EL2_E2PB_MASK << MDCR_EL2_E2PB_SHIFT;
> -
> -	write_sysreg(mdcr_el2, mdcr_el2);
> +	write_sysreg(hyp_host_ctxt->mdcr_el2, mdcr_el2);
>  	write_sysreg(hyp_host_ctxt->hcr_el2, hcr_el2);
>  	write_sysreg(CPTR_EL2_DEFAULT, cptr_el2);
>  }
> @@ -199,15 +195,11 @@ void activate_traps_vhe_load(struct kvm_vcpu *vcpu)
>  	__activate_traps_common(vcpu);
>  }
>  
> -void deactivate_traps_vhe_put(void)
> +void deactivate_traps_vhe_put(struct kvm_vcpu *vcpu)
>  {
> -	u64 mdcr_el2 = read_sysreg(mdcr_el2);
> -
> -	mdcr_el2 &= MDCR_EL2_HPMN_MASK |
> -		    MDCR_EL2_E2PB_MASK << MDCR_EL2_E2PB_SHIFT |
> -		    MDCR_EL2_TPMS;
> +	struct kvm_cpu_context *host_ctxt = vcpu->arch.host_cpu_context;
>  
> -	write_sysreg(mdcr_el2, mdcr_el2);
> +	write_sysreg(host_ctxt->mdcr_el2, mdcr_el2);
>  
>  	__deactivate_traps_common();
>  }
> diff --git a/arch/arm64/kvm/hyp/sysreg-sr.c b/arch/arm64/kvm/hyp/sysreg-sr.c
> index 277f82b..6afd309 100644
> --- a/arch/arm64/kvm/hyp/sysreg-sr.c
> +++ b/arch/arm64/kvm/hyp/sysreg-sr.c
> @@ -298,7 +298,7 @@ void kvm_vcpu_put_sysregs(struct kvm_vcpu *vcpu)
>  	if (!has_vhe())
>  		return;
>  
> -	deactivate_traps_vhe_put();
> +	deactivate_traps_vhe_put(vcpu);
>  
>  	__sysreg_save_el1_state(guest_ctxt);
>  	__sysreg_save_user_state(guest_ctxt);
> @@ -333,4 +333,10 @@ void __hyp_text __kvm_populate_host_regs(void)
>  
>  	host_ctxt = __hyp_this_cpu_ptr(kvm_host_cpu_state);
>  	host_ctxt->hcr_el2 = read_sysreg(hcr_el2);
> +	/*
> +	 * Retrieve the initial value of mdcr_el2 so we can preserve
> +	 * MDCR_EL2.HPMN which has presumably been set-up by some
> +	 * knowledgeable bootcode.
> +	 */
> +	host_ctxt->mdcr_el2 = read_sysreg(mdcr_el2);
>  }
> diff --git a/virt/kvm/arm/arm.c b/virt/kvm/arm/arm.c
> index e8c2ee6..58de0ca 100644
> --- a/virt/kvm/arm/arm.c
> +++ b/virt/kvm/arm/arm.c
> @@ -1322,7 +1322,6 @@ static void cpu_hyp_reinit(void)
>  	else
>  		cpu_init_hyp_mode(NULL);
>  
> -	kvm_arm_init_debug();
>  	cpu_init_host_ctxt();
>  
>  	if (vgic_present)

Looks reasonable overall.

I was wondering whether it would make sense to move some masking into
__kvm_populate_host_regs(), but probably not.

Reviewed-by: Dave Martin <Dave.Martin@....com>

Cheers
---Dave


> -- 
> 2.7.4
> 
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