Subject: Re: [PATCH] kvm: arm/arm64: fold VHE entry/exit work into kvm_vcpu_run_vhe()

From: Marc Zyngier <[email-masked]>
Date: Mon, 17 Feb 2020 14:41:40 +0000

Hi Mark,

On 2020-02-10 11:47, Mark Rutland wrote:
> With VHE, running a vCPU always requires the sequence:
> 
> 1. kvm_arm_vhe_guest_enter();
> 2. kvm_vcpu_run_vhe();
> 3. kvm_arm_vhe_guest_exit()
> 
> ... and as we invoke this from the shared arm/arm64 KVM code, 32-bit 
> arm
> has to provide stubs for all three functions.
> 
> To simplify the common code, and make it easier to make further
> modifications to the arm64-specific portions in the near future, let's
> fold kvm_arm_vhe_guest_enter() and kvm_arm_vhe_guest_exit() into
> kvm_vcpu_run_vhe().
> 
> The 32-bit stubs for kvm_arm_vhe_guest_enter() and
> kvm_arm_vhe_guest_exit() are removed, as they are no longer used. The
> 32-bit stub for kvm_vcpu_run_vhe() is left as-is.
> 
> There should be no functional change as a result of this patch.
> 
> Signed-off-by: Mark Rutland <[email-masked]>
> Cc: Catalin Marinas <[email-masked]>
> Cc: James Morse <[email-masked]>
> Cc: Julien Thierry <[email-masked]>
> Cc: Marc Zyngier <[email-masked]>
> Cc: Suzuki K Poulose <[email-masked]>
> Cc: Will Deacon <[email-masked]>
> Cc: [email-masked]
> ---
>  arch/arm/include/asm/kvm_host.h   |  3 ---
>  arch/arm64/include/asm/kvm_host.h | 32 
> --------------------------------
>  arch/arm64/kvm/hyp/switch.c       | 39 
> +++++++++++++++++++++++++++++++++++++--
>  virt/kvm/arm/arm.c                |  2 --
>  4 files changed, 37 insertions(+), 39 deletions(-)
> 
> Hi Marc,
> 
> This is a preparatory patch for the arm64 entry rework I'm doing: I 
> need to
> move the DAIF manipulation into the same function so that I can replace 
> that
> with a common DAIF+PMR save/restore sequence.
> 
> If it's possible to queue this patch for v5.6-rc*, it would help to 
> minimize
> conflict in the v5.7 merge window, and would be much appreciated.
> 
> I've tested this on a ThunderX2 machine atop v5.6-rc1 defconfig, 
> booting the
> host and running a test VM.
> 
> Thanks,
> Mark.
> 
> diff --git a/arch/arm/include/asm/kvm_host.h 
> b/arch/arm/include/asm/kvm_host.h
> index c3314b286a61..a827b4d60d38 100644
> --- a/arch/arm/include/asm/kvm_host.h
> +++ b/arch/arm/include/asm/kvm_host.h
> @@ -392,9 +392,6 @@ static inline void kvm_arch_vcpu_put_fp(struct
> kvm_vcpu *vcpu) {}
>  static inline void kvm_vcpu_pmu_restore_guest(struct kvm_vcpu *vcpu) 
> {}
>  static inline void kvm_vcpu_pmu_restore_host(struct kvm_vcpu *vcpu) {}
> 
> -static inline void kvm_arm_vhe_guest_enter(void) {}
> -static inline void kvm_arm_vhe_guest_exit(void) {}
> -
>  #define KVM_BP_HARDEN_UNKNOWN		-1
>  #define KVM_BP_HARDEN_WA_NEEDED		0
>  #define KVM_BP_HARDEN_NOT_REQUIRED	1
> diff --git a/arch/arm64/include/asm/kvm_host.h
> b/arch/arm64/include/asm/kvm_host.h
> index d87aa609d2b6..57fd46acd058 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -626,38 +626,6 @@ static inline void kvm_set_pmu_events(u32 set,
> struct perf_event_attr *attr) {}
>  static inline void kvm_clr_pmu_events(u32 clr) {}
>  #endif
> 
> -static inline void kvm_arm_vhe_guest_enter(void)
> -{
> -	local_daif_mask();
> -
> -	/*
> -	 * Having IRQs masked via PMR when entering the guest means the GIC
> -	 * will not signal the CPU of interrupts of lower priority, and the
> -	 * only way to get out will be via guest exceptions.
> -	 * Naturally, we want to avoid this.
> -	 *
> -	 * local_daif_mask() already sets GIC_PRIO_PSR_I_SET, we just need a
> -	 * dsb to ensure the redistributor is forwards EL2 IRQs to the CPU.
> -	 */
> -	pmr_sync();
> -}
> -
> -static inline void kvm_arm_vhe_guest_exit(void)
> -{
> -	/*
> -	 * local_daif_restore() takes care to properly restore PSTATE.DAIF
> -	 * and the GIC PMR if the host is using IRQ priorities.
> -	 */
> -	local_daif_restore(DAIF_PROCCTX_NOIRQ);
> -
> -	/*
> -	 * When we exit from the guest we change a number of CPU 
> configuration
> -	 * parameters, such as traps.  Make sure these changes take effect
> -	 * before running the host or additional guests.
> -	 */
> -	isb();
> -}
> -
>  #define KVM_BP_HARDEN_UNKNOWN		-1
>  #define KVM_BP_HARDEN_WA_NEEDED		0
>  #define KVM_BP_HARDEN_NOT_REQUIRED	1
> diff --git a/arch/arm64/kvm/hyp/switch.c b/arch/arm64/kvm/hyp/switch.c
> index dfe8dd172512..925086b46136 100644
> --- a/arch/arm64/kvm/hyp/switch.c
> +++ b/arch/arm64/kvm/hyp/switch.c
> @@ -625,7 +625,7 @@ static void __hyp_text __pmu_switch_to_host(struct
> kvm_cpu_context *host_ctxt)
>  }
> 
>  /* Switch to the guest for VHE systems running in EL2 */
> -int kvm_vcpu_run_vhe(struct kvm_vcpu *vcpu)
> +static int __kvm_vcpu_run_vhe(struct kvm_vcpu *vcpu)
>  {
>  	struct kvm_cpu_context *host_ctxt;
>  	struct kvm_cpu_context *guest_ctxt;
> @@ -678,7 +678,42 @@ int kvm_vcpu_run_vhe(struct kvm_vcpu *vcpu)
> 
>  	return exit_code;
>  }
> -NOKPROBE_SYMBOL(kvm_vcpu_run_vhe);
> +NOKPROBE_SYMBOL(__kvm_vcpu_run_vhe);
> +
> +int kvm_vcpu_run_vhe(struct kvm_vcpu *vcpu)
> +{
> +	int ret;
> +
> +	local_daif_mask();
> +
> +	/*
> +	 * Having IRQs masked via PMR when entering the guest means the GIC
> +	 * will not signal the CPU of interrupts of lower priority, and the
> +	 * only way to get out will be via guest exceptions.
> +	 * Naturally, we want to avoid this.
> +	 *
> +	 * local_daif_mask() already sets GIC_PRIO_PSR_I_SET, we just need a
> +	 * dsb to ensure the redistributor is forwards EL2 IRQs to the CPU.
> +	 */
> +	pmr_sync();
> +
> +	ret = __kvm_vcpu_run_vhe(vcpu);
> +
> +	/*
> +	 * local_daif_restore() takes care to properly restore PSTATE.DAIF
> +	 * and the GIC PMR if the host is using IRQ priorities.
> +	 */
> +	local_daif_restore(DAIF_PROCCTX_NOIRQ);
> +
> +	/*
> +	 * When we exit from the guest we change a number of CPU 
> configuration
> +	 * parameters, such as traps.  Make sure these changes take effect
> +	 * before running the host or additional guests.
> +	 */
> +	isb();
> +
> +	return ret;
> +}
> 
>  /* Switch to the guest for legacy non-VHE systems */
>  int __hyp_text __kvm_vcpu_run_nvhe(struct kvm_vcpu *vcpu)
> diff --git a/virt/kvm/arm/arm.c b/virt/kvm/arm/arm.c
> index d65a0faa46d8..eda7b624eab8 100644
> --- a/virt/kvm/arm/arm.c
> +++ b/virt/kvm/arm/arm.c
> @@ -742,9 +742,7 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu,
> struct kvm_run *run)
>  		guest_enter_irqoff();
> 
>  		if (has_vhe()) {
> -			kvm_arm_vhe_guest_enter();
>  			ret = kvm_vcpu_run_vhe(vcpu);
> -			kvm_arm_vhe_guest_exit();
>  		} else {
>  			ret = kvm_call_hyp_ret(__kvm_vcpu_run_nvhe, vcpu);
>  		}

Looks good to me, I've taken it as part of the (very small) set of fixes
queued for -rc3.

Thanks,

         M.
-- 
Jazz is not dead. It just smells funny...

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