Subject: [PATCH v5 3/3] KVM/arm/arm64: enable enhanced armv8 fp/simd lazy switch

From: [email-masked] (Mario Smarduch)
Date: Fri, 18 Dec 2015 17:17:00 -0800

On 12/18/2015 5:54 AM, Christoffer Dall wrote:
> On Sun, Dec 06, 2015 at 05:07:14PM -0800, Mario Smarduch wrote:
>> This patch tracks armv7 and armv8 fp/simd hardware state with cptr_el2 register.
>> On vcpu_load for 32 bit guests enable FP access, and enable fp/simd
>> trapping for 32 and 64 bit guests. On first fp/simd access trap to handler 
>> to save host and restore guest context, and clear trapping bits to enable vcpu 
>> lazy mode. On vcpu_put if trap bits are clear save guest and restore host 
>> context and also save 32 bit guest fpexc register.
>>
>> Signed-off-by: Mario Smarduch <[email-masked]>
>> ---
>>  arch/arm/include/asm/kvm_emulate.h   |   5 ++
>>  arch/arm/include/asm/kvm_host.h      |   2 +
>>  arch/arm/kvm/arm.c                   |  20 +++++--
>>  arch/arm64/include/asm/kvm_asm.h     |   2 +
>>  arch/arm64/include/asm/kvm_emulate.h |  15 +++--
>>  arch/arm64/include/asm/kvm_host.h    |  16 +++++-
>>  arch/arm64/kernel/asm-offsets.c      |   1 +
>>  arch/arm64/kvm/Makefile              |   3 +-
>>  arch/arm64/kvm/fpsimd_switch.S       |  38 ++++++++++++
>>  arch/arm64/kvm/hyp.S                 | 108 +++++++++++++----------------------
>>  arch/arm64/kvm/hyp_head.S            |  48 ++++++++++++++++
>>  11 files changed, 181 insertions(+), 77 deletions(-)
>>  create mode 100644 arch/arm64/kvm/fpsimd_switch.S
>>  create mode 100644 arch/arm64/kvm/hyp_head.S
>>
>> diff --git a/arch/arm/include/asm/kvm_emulate.h b/arch/arm/include/asm/kvm_emulate.h
>> index 3de11a2..13feed5 100644
>> --- a/arch/arm/include/asm/kvm_emulate.h
>> +++ b/arch/arm/include/asm/kvm_emulate.h
>> @@ -243,6 +243,11 @@ static inline unsigned long vcpu_data_host_to_guest(struct kvm_vcpu *vcpu,
>>  	}
>>  }
>>  
>> +static inline bool kvm_guest_vcpu_is_32bit(struct kvm_vcpu *vcpu)
>> +{
>> +	return true;
>> +}
>> +
>>  #ifdef CONFIG_VFPv3
>>  /* Called from vcpu_load - save fpexc and enable guest access to fp/simd unit */
>>  static inline void kvm_enable_vcpu_fpexc(struct kvm_vcpu *vcpu)
>> diff --git a/arch/arm/include/asm/kvm_host.h b/arch/arm/include/asm/kvm_host.h
>> index ecc883a..720ae51 100644
>> --- a/arch/arm/include/asm/kvm_host.h
>> +++ b/arch/arm/include/asm/kvm_host.h
>> @@ -227,6 +227,8 @@ int kvm_perf_teardown(void);
>>  void kvm_mmu_wp_memory_region(struct kvm *kvm, int slot);
>>  
>>  struct kvm_vcpu *kvm_mpidr_to_vcpu(struct kvm *kvm, unsigned long mpidr);
>> +
>> +static inline void kvm_save_guest_vcpu_fpexc(struct kvm_vcpu *vcpu) {}
>>  void kvm_restore_host_vfp_state(struct kvm_vcpu *);
>>  
>>  static inline void kvm_arch_hardware_disable(void) {}
>> diff --git a/arch/arm/kvm/arm.c b/arch/arm/kvm/arm.c
>> index 1de07ab..dd59f8a 100644
>> --- a/arch/arm/kvm/arm.c
>> +++ b/arch/arm/kvm/arm.c
>> @@ -292,8 +292,12 @@ void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
>>  
>>  	kvm_arm_set_running_vcpu(vcpu);
>>  
>> -	/*  Save and enable FPEXC before we load guest context */
>> -	kvm_enable_vcpu_fpexc(vcpu);
>> +	/*
>> +	 * For 32bit guest executing on arm64, enable fp/simd access in
>> +	 * EL2. On arm32 save host fpexc and then enable fp/simd access.
>> +	 */
>> +	if (kvm_guest_vcpu_is_32bit(vcpu))
>> +		kvm_enable_vcpu_fpexc(vcpu);
>>  
>>  	/* reset hyp cptr register to trap on tracing and vfp/simd access*/
>>  	vcpu_reset_cptr(vcpu);
>> @@ -302,10 +306,18 @@ void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
>>  void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu)
>>  {
>>  	/* If the fp/simd registers are dirty save guest, restore host. */
>> -	if (kvm_vcpu_vfp_isdirty(vcpu))
>> +	if (kvm_vcpu_vfp_isdirty(vcpu)) {
>>  		kvm_restore_host_vfp_state(vcpu);
>>  
>> -	/* Restore host FPEXC trashed in vcpu_load */
>> +		/*
>> +		 * For 32bit guest on arm64 save the guest fpexc register
>> +		 * in EL2 mode.
>> +		 */
>> +		if (kvm_guest_vcpu_is_32bit(vcpu))
>> +			kvm_save_guest_vcpu_fpexc(vcpu);
>> +	}
>> +
>> +	/* For arm32 restore host FPEXC trashed in vcpu_load. */
>>  	kvm_restore_host_fpexc(vcpu);
>>  
>>  	/*
>> diff --git a/arch/arm64/include/asm/kvm_asm.h b/arch/arm64/include/asm/kvm_asm.h
>> index 5e37710..d53d069 100644
>> --- a/arch/arm64/include/asm/kvm_asm.h
>> +++ b/arch/arm64/include/asm/kvm_asm.h
>> @@ -117,6 +117,8 @@ extern char __kvm_hyp_vector[];
>>  extern void __kvm_flush_vm_context(void);
>>  extern void __kvm_tlb_flush_vmid_ipa(struct kvm *kvm, phys_addr_t ipa);
>>  extern void __kvm_tlb_flush_vmid(struct kvm *kvm);
>> +extern void __kvm_vcpu_enable_fpexc32(void);
>> +extern void __kvm_vcpu_save_fpexc32(struct kvm_vcpu *vcpu);
>>  
>>  extern int __kvm_vcpu_run(struct kvm_vcpu *vcpu);
>>  
>> diff --git a/arch/arm64/include/asm/kvm_emulate.h b/arch/arm64/include/asm/kvm_emulate.h
>> index 8dccbd7..bbbee9d 100644
>> --- a/arch/arm64/include/asm/kvm_emulate.h
>> +++ b/arch/arm64/include/asm/kvm_emulate.h
>> @@ -290,13 +290,20 @@ static inline unsigned long vcpu_data_host_to_guest(struct kvm_vcpu *vcpu,
>>  	return data;		/* Leave LE untouched */
>>  }
>>  
>> -static inline void kvm_enable_vcpu_fpexc(struct kvm_vcpu *vcpu) {}
>> -static inline void kvm_restore_host_fpexc(struct kvm_vcpu *vcpu) {}
>> -static inline void vcpu_reset_cptr(struct kvm_vcpu *vcpu) {}
>> +static inline bool kvm_guest_vcpu_is_32bit(struct kvm_vcpu *vcpu)
>> +{
>> +	 return !(vcpu->arch.hcr_el2 & HCR_RW);
>> +}
>> +
>> +static inline void vcpu_reset_cptr(struct kvm_vcpu *vcpu)
>> +{
>> +	vcpu->arch.cptr_el2 = CPTR_EL2_TTA | CPTR_EL2_TFP;
>> +}
>> +
>>  
>>  static inline bool kvm_vcpu_vfp_isdirty(struct kvm_vcpu *vcpu)
>>  {
>> -	return false;
>> +	return !!(~vcpu->arch.cptr_el2 & CPTR_EL2_TFP);
>>  }
>>  
>>  #endif /* __ARM64_KVM_EMULATE_H__ */
>> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
>> index e16fd39..0c65393 100644
>> --- a/arch/arm64/include/asm/kvm_host.h
>> +++ b/arch/arm64/include/asm/kvm_host.h
>> @@ -100,6 +100,7 @@ struct kvm_vcpu_arch {
>>  	/* HYP configuration */
>>  	u64 hcr_el2;
>>  	u32 mdcr_el2;
>> +	u32 cptr_el2;
>>  
>>  	/* Exception Information */
>>  	struct kvm_vcpu_fault_info fault;
>> @@ -248,7 +249,20 @@ static inline void kvm_arch_hardware_unsetup(void) {}
>>  static inline void kvm_arch_sync_events(struct kvm *kvm) {}
>>  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_restore_host_vfp_state(struct kvm_vcpu *vcpu) {}
>> +
>> +static inline void kvm_enable_vcpu_fpexc(struct kvm_vcpu *vcpu)
>> +{
>> +	/* Enable FP/SIMD access from EL2 mode*/
>> +	kvm_call_hyp(__kvm_vcpu_enable_fpexc32);
>> +}
>> +
>> +static inline void kvm_save_guest_vcpu_fpexc(struct kvm_vcpu *vcpu)
>> +{
>> +	/* Save FPEXEC32_EL2 in EL2 mode */
>> +	kvm_call_hyp(__kvm_vcpu_save_fpexc32, vcpu);
>> +}
>> +static inline void kvm_restore_host_fpexc(struct kvm_vcpu *vcpu) {}
>> +void kvm_restore_host_vfp_state(struct kvm_vcpu *vcpu);
>>  
>>  void kvm_arm_init_debug(void);
>>  void kvm_arm_setup_debug(struct kvm_vcpu *vcpu);
>> diff --git a/arch/arm64/kernel/asm-offsets.c b/arch/arm64/kernel/asm-offsets.c
>> index 8d89cf8..3c8d836 100644
>> --- a/arch/arm64/kernel/asm-offsets.c
>> +++ b/arch/arm64/kernel/asm-offsets.c
>> @@ -123,6 +123,7 @@ int main(void)
>>    DEFINE(DEBUG_WVR, 		offsetof(struct kvm_guest_debug_arch, dbg_wvr));
>>    DEFINE(VCPU_HCR_EL2,		offsetof(struct kvm_vcpu, arch.hcr_el2));
>>    DEFINE(VCPU_MDCR_EL2,	offsetof(struct kvm_vcpu, arch.mdcr_el2));
>> +  DEFINE(VCPU_CPTR_EL2,		offsetof(struct kvm_vcpu, arch.cptr_el2));
>>    DEFINE(VCPU_IRQ_LINES,	offsetof(struct kvm_vcpu, arch.irq_lines));
>>    DEFINE(VCPU_HOST_CONTEXT,	offsetof(struct kvm_vcpu, arch.host_cpu_context));
>>    DEFINE(VCPU_HOST_DEBUG_STATE, offsetof(struct kvm_vcpu, arch.host_debug_state));
>> diff --git a/arch/arm64/kvm/Makefile b/arch/arm64/kvm/Makefile
>> index 1949fe5..262b9a5 100644
>> --- a/arch/arm64/kvm/Makefile
>> +++ b/arch/arm64/kvm/Makefile
>> @@ -17,7 +17,8 @@ kvm-$(CONFIG_KVM_ARM_HOST) += $(ARM)/psci.o $(ARM)/perf.o
>>  
>>  kvm-$(CONFIG_KVM_ARM_HOST) += emulate.o inject_fault.o regmap.o
>>  kvm-$(CONFIG_KVM_ARM_HOST) += hyp.o hyp-init.o handle_exit.o
>> -kvm-$(CONFIG_KVM_ARM_HOST) += guest.o debug.o reset.o sys_regs.o sys_regs_generic_v8.o
>> +kvm-$(CONFIG_KVM_ARM_HOST) += guest.o debug.o reset.o sys_regs.o
>> +kvm-$(CONFIG_KVM_ARM_HOST) += sys_regs_generic_v8.o fpsimd_switch.o
>>  
>>  kvm-$(CONFIG_KVM_ARM_HOST) += $(KVM)/arm/vgic.o
>>  kvm-$(CONFIG_KVM_ARM_HOST) += $(KVM)/arm/vgic-v2.o
>> diff --git a/arch/arm64/kvm/fpsimd_switch.S b/arch/arm64/kvm/fpsimd_switch.S
>> new file mode 100644
>> index 0000000..5295512
>> --- /dev/null
>> +++ b/arch/arm64/kvm/fpsimd_switch.S
>> @@ -0,0 +1,38 @@
>> +/*
>> + * Copyright (C) 2012,2013 - ARM Ltd
>> + * Author: Marc Zyngier <[email-masked]>
>> + *
> 
> Is this copied code or new code?

It's mostly refactored copied code.
> 
>> + * 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 "hyp_head.S"
>> +
>> +	.text
>> +/**
>> + * void kvm_restore_host_vfp_state(struct vcpu *vcpu) -
>> + *     This function saves the guest, restores host, called from host.
>> + */
>> +ENTRY(kvm_restore_host_vfp_state)
>> +	push	xzr, lr
>> +
>> +	add	x2, x0, #VCPU_CONTEXT
>> +	bl __save_fpsimd
>> +
>> +	ldr	x2, [x0, #VCPU_HOST_CONTEXT]
>> +	bl __restore_fpsimd
>> +
>> +	pop	xzr, lr
>> +	ret
>> +ENDPROC(kvm_restore_host_vfp_state)
>> diff --git a/arch/arm64/kvm/hyp.S b/arch/arm64/kvm/hyp.S
>> index e583613..b8b1afb 100644
>> --- a/arch/arm64/kvm/hyp.S
>> +++ b/arch/arm64/kvm/hyp.S
>> @@ -17,23 +17,7 @@
>>  
>>  #include <linux/linkage.h>
>>  
>> -#include <asm/alternative.h>
>> -#include <asm/asm-offsets.h>
>> -#include <asm/assembler.h>
>> -#include <asm/cpufeature.h>
>> -#include <asm/debug-monitors.h>
>> -#include <asm/esr.h>
>> -#include <asm/fpsimdmacros.h>
>> -#include <asm/kvm.h>
>> -#include <asm/kvm_arm.h>
>> -#include <asm/kvm_asm.h>
>> -#include <asm/kvm_mmu.h>
>> -#include <asm/memory.h>
>> -
>> -#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_SPSR_OFFSET(x)	CPU_GP_REG_OFFSET(CPU_SPSR + 8*x)
>> -#define CPU_SYSREG_OFFSET(x)	(CPU_SYSREGS + 8*x)
>> +#include "hyp_head.S"
>>  
>>  	.text
>>  	.pushsection	.hyp.text, "ax"
>> @@ -104,20 +88,6 @@
>>  	restore_common_regs
>>  .endm
>>  
>> -.macro save_fpsimd
>> -	// x2: cpu context address
>> -	// x3, x4: tmp regs
>> -	add	x3, x2, #CPU_GP_REG_OFFSET(CPU_FP_REGS)
>> -	fpsimd_save x3, 4
>> -.endm
>> -
>> -.macro restore_fpsimd
>> -	// x2: cpu context address
>> -	// x3, x4: tmp regs
>> -	add	x3, x2, #CPU_GP_REG_OFFSET(CPU_FP_REGS)
>> -	fpsimd_restore x3, 4
>> -.endm
>> -
>>  .macro save_guest_regs
>>  	// x0 is the vcpu address
>>  	// x1 is the return code, do not corrupt!
>> @@ -385,14 +355,6 @@
>>  	tbz	\tmp, #KVM_ARM64_DEBUG_DIRTY_SHIFT, \target
>>  .endm
>>  
>> -/*
>> - * Branch to target if CPTR_EL2.TFP bit is set (VFP/SIMD trapping enabled)
>> - */
>> -.macro skip_fpsimd_state tmp, target
>> -	mrs	\tmp, cptr_el2
>> -	tbnz	\tmp, #CPTR_EL2_TFP_SHIFT, \target
>> -.endm
>> -
>>  .macro compute_debug_state target
>>  	// Compute debug state: If any of KDE, MDE or KVM_ARM64_DEBUG_DIRTY
>>  	// is set, we do a full save/restore cycle and disable trapping.
>> @@ -433,10 +395,6 @@
>>  	mrs	x5, ifsr32_el2
>>  	stp	x4, x5, [x3]
>>  
>> -	skip_fpsimd_state x8, 2f
>> -	mrs	x6, fpexc32_el2
>> -	str	x6, [x3, #16]
>> -2:
>>  	skip_debug_state x8, 1f
>>  	mrs	x7, dbgvcr32_el2
>>  	str	x7, [x3, #24]
>> @@ -467,22 +425,9 @@
>>  
>>  .macro activate_traps
>>  	ldr     x2, [x0, #VCPU_HCR_EL2]
>> -
>> -	/*
>> -	 * We are about to set CPTR_EL2.TFP to trap all floating point
>> -	 * register accesses to EL2, however, the ARM ARM clearly states that
>> -	 * traps are only taken to EL2 if the operation would not otherwise
>> -	 * trap to EL1.  Therefore, always make sure that for 32-bit guests,
>> -	 * we set FPEXC.EN to prevent traps to EL1, when setting the TFP bit.
>> -	 */
>> -	tbnz	x2, #HCR_RW_SHIFT, 99f // open code skip_32bit_state
>> -	mov	x3, #(1 << 30)
>> -	msr	fpexc32_el2, x3
>> -	isb
>> -99:
>>  	msr     hcr_el2, x2
>> -	mov	x2, #CPTR_EL2_TTA
>> -	orr     x2, x2, #CPTR_EL2_TFP
>> +
>> +	ldr     w2, [x0, VCPU_CPTR_EL2]
>>  	msr	cptr_el2, x2
>>  
>>  	mov	x2, #(1 << 15)	// Trap CP15 Cr=15
>> @@ -668,15 +613,15 @@ __restore_debug:
>>  
>>  	ret
>>  
>> -__save_fpsimd:
>> -	skip_fpsimd_state x3, 1f
>> +ENTRY(__save_fpsimd)
>>  	save_fpsimd
>> -1:	ret
>> +	ret
>> +ENDPROC(__save_fpsimd)
>>  
>> -__restore_fpsimd:
>> -	skip_fpsimd_state x3, 1f
>> +ENTRY(__restore_fpsimd)
>>  	restore_fpsimd
>> -1:	ret
>> +	ret
>> +ENDPROC(__restore_fpsimd)
>>  
>>  switch_to_guest_fpsimd:
>>  	push	x4, lr
>> @@ -763,7 +708,6 @@ __kvm_vcpu_return:
>>  	add	x2, x0, #VCPU_CONTEXT
>>  
>>  	save_guest_regs
>> -	bl __save_fpsimd
>>  	bl __save_sysregs
>>  
>>  	skip_debug_state x3, 1f
>> @@ -784,8 +728,10 @@ __kvm_vcpu_return:
>>  	kern_hyp_va x2
>>  
>>  	bl __restore_sysregs
>> -	bl __restore_fpsimd
>> -	/* Clear FPSIMD and Trace trapping */
>> +
>> +	/* Save CPTR_EL2 between exits and clear FPSIMD and Trace trapping */
>> +	mrs     x3, cptr_el2
>> +	str     w3, [x0, VCPU_CPTR_EL2]
>>  	msr     cptr_el2, xzr
>>  
>>  	skip_debug_state x3, 1f
>> @@ -863,6 +809,34 @@ ENTRY(__kvm_flush_vm_context)
>>  	ret
>>  ENDPROC(__kvm_flush_vm_context)
>>  
>> +/**
>> +  * void __kvm_enable_fpexc32(void) -
>> +  *	We may be entering the guest and set CPTR_EL2.TFP to trap all floating
>> +  *	point register accesses to EL2, however, the ARM manual clearly states
>> +  *	that traps are only taken to EL2 if the operation would not otherwise
>> +  *	trap to EL1.  Therefore, always make sure that for 32-bit guests,
>> +  *	we set FPEXC.EN to prevent traps to EL1, when setting the TFP bit.
>> +  */
>> +ENTRY(__kvm_vcpu_enable_fpexc32)
>> +	mov	x3, #(1 << 30)
>> +	msr	fpexc32_el2, x3
>> +	isb
> 
> this is only called via a hypercall so do you really need the ISB?

Same comment as in 2nd patch for the isb.

> 
>> +	ret
>> +ENDPROC(__kvm_vcpu_enable_fpexc32)
>> +
>> +/**
>> + * void __kvm_save_fpexc32(void) -
>> + *	This function restores guest FPEXC to its vcpu context, we call this
>> + *	function from vcpu_put.
>> + */
>> +ENTRY(__kvm_vcpu_save_fpexc32)
>> +	kern_hyp_va x0
>> +	add     x2, x0, #VCPU_CONTEXT
>> +	mrs     x1, fpexc32_el2
>> +	str     x1, [x2, #CPU_SYSREG_OFFSET(FPEXC32_EL2)]
>> +	ret
>> +ENDPROC(__kvm_vcpu_save_fpexc32)
>> +
>>  __kvm_hyp_panic:
>>  	// Guess the context by looking at VTTBR:
>>  	// If zero, then we're already a host.
>> diff --git a/arch/arm64/kvm/hyp_head.S b/arch/arm64/kvm/hyp_head.S
>> new file mode 100644
>> index 0000000..bb32824
>> --- /dev/null
>> +++ b/arch/arm64/kvm/hyp_head.S
>> @@ -0,0 +1,48 @@
>> +/*
>> + * Copyright (C) 2012,2013 - ARM Ltd
>> + * Author: Marc Zyngier <[email-masked]>
>> + *
>> + * 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 <asm/alternative.h>
>> +#include <asm/asm-offsets.h>
>> +#include <asm/assembler.h>
>> +#include <asm/cpufeature.h>
>> +#include <asm/debug-monitors.h>
>> +#include <asm/esr.h>
>> +#include <asm/fpsimdmacros.h>
>> +#include <asm/kvm.h>
>> +#include <asm/kvm_arm.h>
>> +#include <asm/kvm_asm.h>
>> +#include <asm/kvm_mmu.h>
>> +#include <asm/memory.h>
>> +
>> +#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_SPSR_OFFSET(x)      CPU_GP_REG_OFFSET(CPU_SPSR + 8*x)
>> +#define CPU_SYSREG_OFFSET(x)    (CPU_SYSREGS + 8*x)
>> +
>> +.macro save_fpsimd
>> +	// x2: cpu context address
>> +	// x3, x4: tmp regs
>> +	add x3, x2, #CPU_GP_REG_OFFSET(CPU_FP_REGS)
>> +	fpsimd_save x3, 4
>> +.endm
>> +
>> +.macro restore_fpsimd
>> +	// x2: cpu context address
>> +	// x3, x4: tmp regs
>> +	add x3, x2, #CPU_GP_REG_OFFSET(CPU_FP_REGS)
>> +	fpsimd_restore x3, 4
>> +.endm
>> -- 
>> 1.9.1
>>
> 
> I'm not going to review the details of this, since we have to rebase it
> on the world-switch in C, sorry.
That fine.
> 
> The good news is that it should be much simpler to write in C-code.
> 
> Let me know if you don't have the bandwidth to rebase this, in that case
> I'll be happy to help.

Let me see where I'm at by the end of Monday, if there is a rush to get it into
next release by all means.

> Thanks,
> -Christoffer