Re: [PATCH v2 12/21] arm64: KVM: Implement fpsimd save/restore

[Christoffer Dall <christoffer.dall@linaro.org>]

On Fri, Nov 27, 2015 at 06:50:06PM +0000, Marc Zyngier wrote:
> Implement the fpsimd save restore, keeping the lazy part in
> assembler (as returning to C would be overkill).
> 
> Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
> ---
>  arch/arm64/kvm/hyp/Makefile    |  1 +
>  arch/arm64/kvm/hyp/entry.S     | 32 +++++++++++++++++++++++++++++++-
>  arch/arm64/kvm/hyp/fpsimd.S    | 33 +++++++++++++++++++++++++++++++++
>  arch/arm64/kvm/hyp/hyp.h       |  7 +++++++
>  arch/arm64/kvm/hyp/switch.c    |  8 ++++++++
>  arch/arm64/kvm/hyp/sysreg-sr.c |  2 +-
>  6 files changed, 81 insertions(+), 2 deletions(-)
>  create mode 100644 arch/arm64/kvm/hyp/fpsimd.S
> 
> diff --git a/arch/arm64/kvm/hyp/Makefile b/arch/arm64/kvm/hyp/Makefile
> index 9c11b0f..56238d0 100644
> --- a/arch/arm64/kvm/hyp/Makefile
> +++ b/arch/arm64/kvm/hyp/Makefile
> @@ -9,3 +9,4 @@ obj-$(CONFIG_KVM_ARM_HOST) += sysreg-sr.o
>  obj-$(CONFIG_KVM_ARM_HOST) += debug-sr.o
>  obj-$(CONFIG_KVM_ARM_HOST) += entry.o
>  obj-$(CONFIG_KVM_ARM_HOST) += switch.o
> +obj-$(CONFIG_KVM_ARM_HOST) += fpsimd.o
> diff --git a/arch/arm64/kvm/hyp/entry.S b/arch/arm64/kvm/hyp/entry.S
> index 2c4449a..7552922 100644
> --- a/arch/arm64/kvm/hyp/entry.S
> +++ b/arch/arm64/kvm/hyp/entry.S
> @@ -27,6 +27,7 @@
>  
>  #define CPU_GP_REG_OFFSET(x)	(CPU_GP_REGS + x)
>  #define CPU_XREG_OFFSET(x)	CPU_GP_REG_OFFSET(CPU_USER_PT_REGS + 8*x)
> +#define CPU_SYSREG_OFFSET(x)	(CPU_SYSREGS + 8*x)
>  
>  	.text
>  	.pushsection	.hyp.text, "ax"
> @@ -152,4 +153,33 @@ ENTRY(__guest_exit)
>  	ret
>  ENDPROC(__guest_exit)
>  
> -	/* Insert fault handling here */
> +ENTRY(__fpsimd_guest_restore)
> +	push	x4, lr
> +
> +	mrs	x2, cptr_el2
> +	bic	x2, x2, #CPTR_EL2_TFP
> +	msr	cptr_el2, x2
> +	isb
> +
> +	mrs	x3, tpidr_el2
> +
> +	ldr	x0, [x3, #VCPU_HOST_CONTEXT]
> +	kern_hyp_va x0
> +	add	x0, x0, #CPU_GP_REG_OFFSET(CPU_FP_REGS)
> +	bl	__fpsimd_save_state
> +
> +	add	x2, x3, #VCPU_CONTEXT
> +	add	x0, x2, #CPU_GP_REG_OFFSET(CPU_FP_REGS)
> +	bl	__fpsimd_restore_state
> +
> +	mrs	x1, hcr_el2
> +	tbnz	x1, #HCR_RW_SHIFT, 1f

nit: Add a comment along the lines of:
// Skip restoring fpexc32 for AArch64 guests

> +	ldr	x4, [x2, #CPU_SYSREG_OFFSET(FPEXC32_EL2)]
> +	msr	fpexc32_el2, x4
> +1:
> +	pop	x4, lr
> +	pop	x2, x3
> +	pop	x0, x1
> +
> +	eret
> +ENDPROC(__fpsimd_guest_restore)
> diff --git a/arch/arm64/kvm/hyp/fpsimd.S b/arch/arm64/kvm/hyp/fpsimd.S
> new file mode 100644
> index 0000000..da3f22c
> --- /dev/null
> +++ b/arch/arm64/kvm/hyp/fpsimd.S
> @@ -0,0 +1,33 @@
> +/*
> + * Copyright (C) 2015 - ARM Ltd
> + * Author: Marc Zyngier <marc.zyngier@arm.com>
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License version 2 as
> + * published by the Free Software Foundation.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> + * GNU General Public License for more details.
> + *
> + * You should have received a copy of the GNU General Public License
> + * along with this program.  If not, see <http://www.gnu.org/licenses/>.
> + */
> +
> +#include <linux/linkage.h>
> +
> +#include <asm/fpsimdmacros.h>
> +
> +	.text
> +	.pushsection	.hyp.text, "ax"
> +
> +ENTRY(__fpsimd_save_state)
> +	fpsimd_save	x0, 1
> +	ret
> +ENDPROC(__fpsimd_save_state)
> +
> +ENTRY(__fpsimd_restore_state)
> +	fpsimd_restore	x0, 1
> +	ret
> +ENDPROC(__fpsimd_restore_state)
> diff --git a/arch/arm64/kvm/hyp/hyp.h b/arch/arm64/kvm/hyp/hyp.h
> index f0427ee..18365dd 100644
> --- a/arch/arm64/kvm/hyp/hyp.h
> +++ b/arch/arm64/kvm/hyp/hyp.h
> @@ -66,6 +66,13 @@ void __debug_restore_state(struct kvm_vcpu *vcpu,
>  void __debug_cond_save_host_state(struct kvm_vcpu *vcpu);
>  void __debug_cond_restore_host_state(struct kvm_vcpu *vcpu);
>  
> +void __fpsimd_save_state(struct user_fpsimd_state *fp_regs);
> +void __fpsimd_restore_state(struct user_fpsimd_state *fp_regs);
> +static inline bool __fpsimd_enabled(void)
> +{
> +	return !(read_sysreg(cptr_el2) & CPTR_EL2_TFP);
> +}
> +
>  u64 __guest_enter(struct kvm_vcpu *vcpu, struct kvm_cpu_context *host_ctxt);
>  
>  #endif /* __ARM64_KVM_HYP_H__ */
> diff --git a/arch/arm64/kvm/hyp/switch.c b/arch/arm64/kvm/hyp/switch.c
> index d67ed9e..8affc19 100644
> --- a/arch/arm64/kvm/hyp/switch.c
> +++ b/arch/arm64/kvm/hyp/switch.c
> @@ -88,6 +88,7 @@ int __hyp_text __guest_run(struct kvm_vcpu *vcpu)
>  {
>  	struct kvm_cpu_context *host_ctxt;
>  	struct kvm_cpu_context *guest_ctxt;
> +	bool fp_enabled;
>  	u64 exit_code;
>  
>  	vcpu = kern_hyp_va(vcpu);
> @@ -117,6 +118,8 @@ int __hyp_text __guest_run(struct kvm_vcpu *vcpu)
>  	exit_code = __guest_enter(vcpu, host_ctxt);
>  	/* And we're baaack! */
>  
> +	fp_enabled = __fpsimd_enabled();
> +

what does 'enabled' really mean here?  Isn't it really
__fpsimd_is_dirty() or __fpsimd_is_guest() or something like that (I
suck at naming too).

>  	__sysreg_save_state(guest_ctxt);
>  	__sysreg32_save_state(vcpu);
>  	__timer_save_state(vcpu);
> @@ -127,6 +130,11 @@ int __hyp_text __guest_run(struct kvm_vcpu *vcpu)
>  
>  	__sysreg_restore_state(host_ctxt);
>  
> +	if (fp_enabled) {
> +		__fpsimd_save_state(&guest_ctxt->gp_regs.fp_regs);
> +		__fpsimd_restore_state(&host_ctxt->gp_regs.fp_regs);
> +	}
> +
>  	__debug_save_state(vcpu, kern_hyp_va(vcpu->arch.debug_ptr), guest_ctxt);
>  	__debug_cond_restore_host_state(vcpu);
>  
> diff --git a/arch/arm64/kvm/hyp/sysreg-sr.c b/arch/arm64/kvm/hyp/sysreg-sr.c
> index 3f81a4d..41b9d30 100644
> --- a/arch/arm64/kvm/hyp/sysreg-sr.c
> +++ b/arch/arm64/kvm/hyp/sysreg-sr.c
> @@ -103,7 +103,7 @@ void __hyp_text __sysreg32_save_state(struct kvm_vcpu *vcpu)
>  		sysreg[DACR32_EL2] = read_sysreg(dacr32_el2);
>  		sysreg[IFSR32_EL2] = read_sysreg(ifsr32_el2);
>  
> -		if (!(read_sysreg(cptr_el2) & CPTR_EL2_TFP))
> +		if (__fpsimd_enabled())
>  			sysreg[FPEXC32_EL2] = read_sysreg(fpexc32_el2);
>  
>  		if (vcpu->arch.debug_flags & KVM_ARM64_DEBUG_DIRTY)
> -- 
> 2.1.4
> 

Otherwise:

Reviewed-by: Christoffer Dall <christoffer.dall@linaro.org>