[RFC PATCH 8/8] KVM: arm64: Remove eager host SVE state saving

[Christoffer Dall]

On Fri, Apr 20, 2018 at 05:46:42PM +0100, Dave Martin wrote:
> Now that the host SVE context can be saved on demand from Hyp,
> there is no longer any need to save this state in advance before
> entering the guest.
> 
> This patch removes the relevant call to
> kvm_fpsimd_flush_cpu_state().
> 
> Since the problem that function was intended to solve now no longer
> exists, the function and its dependencies are also deleted.
> 
> Signed-off-by: Dave Martin <Dave.Martin at arm.com>
> ---
>  arch/arm/include/asm/kvm_host.h   |  3 ---
>  arch/arm64/include/asm/kvm_host.h | 10 ----------
>  arch/arm64/kernel/fpsimd.c        | 21 ---------------------
>  virt/kvm/arm/arm.c                |  3 ---
>  4 files changed, 37 deletions(-)
> 
> diff --git a/arch/arm/include/asm/kvm_host.h b/arch/arm/include/asm/kvm_host.h
> index 3fe01c7..cf268cb 100644
> --- a/arch/arm/include/asm/kvm_host.h
> +++ b/arch/arm/include/asm/kvm_host.h
> @@ -308,9 +308,6 @@ static inline void kvm_arch_vcpu_load_fp(struct kvm_vcpu *vcpu) {}
>  static inline void kvm_arch_vcpu_park_fp(struct kvm_vcpu *vcpu) {}
>  static inline void kvm_arch_vcpu_put_fp(struct kvm_vcpu *vcpu) {}
>  
> -/* All host FP/SIMD state is restored on guest exit, so nothing to save: */
> -static inline void kvm_fpsimd_flush_cpu_state(void) {}
> -
>  static inline void kvm_arm_vhe_guest_enter(void) {}
>  static inline void kvm_arm_vhe_guest_exit(void) {}
>  
> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index 2fbfbda..df52254 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -435,16 +435,6 @@ static inline int kvm_arch_vcpu_run_pid_change(struct kvm_vcpu *vcpu)
>  	return kvm_arch_vcpu_run_map_fp(vcpu);
>  }
>  
> -/*
> - * All host FP/SIMD state is restored on guest exit, so nothing needs
> - * doing here except in the SVE case:
> -*/
> -static inline void kvm_fpsimd_flush_cpu_state(void)
> -{
> -	if (system_supports_sve())
> -		sve_flush_cpu_state();
> -}
> -
>  static inline void kvm_arm_vhe_guest_enter(void)
>  {
>  	local_daif_mask();
> diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c
> index fa4f6e2..cdfbcf7 100644
> --- a/arch/arm64/kernel/fpsimd.c
> +++ b/arch/arm64/kernel/fpsimd.c
> @@ -120,7 +120,6 @@
>   */
>  struct fpsimd_last_state_struct {
>  	struct user_fpsimd_state *st;
> -	bool sve_in_use;
>  };
>  
>  static DEFINE_PER_CPU(struct fpsimd_last_state_struct, fpsimd_last_state);
> @@ -1025,7 +1024,6 @@ static void fpsimd_bind_to_cpu(void)
>  		this_cpu_ptr(&fpsimd_last_state);
>  
>  	last->st = &current->thread.uw.fpsimd_state;
> -	last->sve_in_use = test_thread_flag(TIF_SVE);
>  	current->thread.fpsimd_cpu = smp_processor_id();
>  }
>  
> @@ -1037,7 +1035,6 @@ void fpsimd_bind_state_to_cpu(struct user_fpsimd_state *st)
>  	WARN_ON(!in_softirq() && !irqs_disabled());
>  
>  	last->st = st;
> -	last->sve_in_use = false;
>  }
>  
>  /*
> @@ -1097,24 +1094,6 @@ void fpsimd_flush_cpu_state(void)
>  	__this_cpu_write(fpsimd_last_state.st, NULL);
>  }
>  
> -/*
> - * Invalidate any task SVE state currently held in this CPU's regs.
> - *
> - * This is used to prevent the kernel from trying to reuse SVE register data
> - * that is detroyed by KVM guest enter/exit.  This function should go away when
> - * KVM SVE support is implemented.  Don't use it for anything else.
> - */
> -#ifdef CONFIG_ARM64_SVE
> -void sve_flush_cpu_state(void)
> -{
> -	struct fpsimd_last_state_struct const *last =
> -		this_cpu_ptr(&fpsimd_last_state);
> -
> -	if (last->st && last->sve_in_use)
> -		fpsimd_flush_cpu_state();
> -}
> -#endif /* CONFIG_ARM64_SVE */
> -
>  #ifdef CONFIG_KERNEL_MODE_NEON
>  
>  DEFINE_PER_CPU(bool, kernel_neon_busy);
> diff --git a/virt/kvm/arm/arm.c b/virt/kvm/arm/arm.c
> index 147d9d9..501cacb 100644
> --- a/virt/kvm/arm/arm.c
> +++ b/virt/kvm/arm/arm.c
> @@ -693,9 +693,6 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *run)
>  		 */
>  		preempt_disable();
>  
> -		/* Flush FP/SIMD state that can't survive guest entry/exit */
> -		kvm_fpsimd_flush_cpu_state();
> -
>  		kvm_pmu_flush_hwstate(vcpu);
>  
>  		local_irq_disable();
> -- 
> 2.1.4
> 
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Acked-by: Christoffer Dall <christoffer.dall at arm.com>