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

From: [email-masked] (Christoffer Dall)
Date: Fri, 18 Dec 2015 14:54:03 +0100

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?

> + * 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?

> +	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.

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.

Thanks,
-Christoffer