Date:	Wed, 08 Jul 2015 18:29:52 -0700
From:	Mario Smarduch <m.smarduch@...sung.com>
To:	Marc Zyngier <marc.zyngier@....com>
Cc:	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	Christoffer Dall <christoffer.dall@...aro.org>,
	kvmarm@...ts.cs.columbia.edu, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, kvm@...r.kernel.org
Subject: Re: [PATCH 09/13] arm64: KVM: VHE: Add alternatives for VHE-enabled
 world-switch

On 07/08/2015 09:19 AM, Marc Zyngier wrote:
> In order to switch between host and guest, a VHE-enabled kernel
> must use different accessors for certain system registers.
> 
> This patch uses runtime patching to use the right instruction
> when required...
> 
> Signed-off-by: Marc Zyngier <marc.zyngier@....com>
> ---
>  arch/arm64/include/asm/kvm_asm.h |  40 ++++++--
>  arch/arm64/kvm/hyp.S             | 210 ++++++++++++++++++++++++++-------------
>  arch/arm64/kvm/vhe-macros.h      |  18 ++++
>  3 files changed, 191 insertions(+), 77 deletions(-)
> 
[....]
>   * Author: Marc Zyngier <marc.zyngier@....com>
>   *
>   * This program is free software; you can redistribute it and/or modify
> @@ -67,40 +67,52 @@
>  	stp	x29, lr, [x3, #80]
>  
>  	mrs	x19, sp_el0
> -	mrs	x20, elr_el2		// pc before entering el2
> -	mrs	x21, spsr_el2		// pstate before entering el2
> +	str	x19, [x3, #96]
> +.endm
>  
> -	stp	x19, x20, [x3, #96]
> -	str	x21, [x3, #112]

Hi Marc,

  trying to make a little sense out of this :)

In the case of VHE kernel the two 'mrs_hyp()' and 'mrs_el1()'
calls would  be accessing same registers - namely EL1 variants?
For non VHE EL2, EL1?

The mrs_s and sysreg_EL12 are new, not sure what these mean.

- Mario

> +.macro save_el1_state
> +	mrs_hyp(x20, ELR)		// pc before entering el2
> +	mrs_hyp(x21, SPSR)		// pstate before entering el2
>  
>  	mrs	x22, sp_el1
> -	mrs	x23, elr_el1
> -	mrs	x24, spsr_el1
> +
> +	mrs_el1(x23, elr)
> +	mrs_el1(x24, spsr)
> +
> +	add	x3, x2, #CPU_XREG_OFFSET(31)	// SP_EL0
> +	stp	x20, x21, [x3, #8]	// HACK: Store to the regs after SP_EL0
>  
>  	str	x22, [x2, #CPU_GP_REG_OFFSET(CPU_SP_EL1)]
>  	str	x23, [x2, #CPU_GP_REG_OFFSET(CPU_ELR_EL1)]
>  	str	x24, [x2, #CPU_SPSR_OFFSET(KVM_SPSR_EL1)]
>  .endm
>  
> -.macro restore_common_regs
> +.macro restore_el1_state
>  	// x2: base address for cpu context
>  	// x3: tmp register
>  
> +	add	x3, x2, #CPU_XREG_OFFSET(31)    // SP_EL0
> +	ldp	x20, x21, [x3, #8] // Same hack again, get guest PC and pstate
> +
>  	ldr	x22, [x2, #CPU_GP_REG_OFFSET(CPU_SP_EL1)]
>  	ldr	x23, [x2, #CPU_GP_REG_OFFSET(CPU_ELR_EL1)]
>  	ldr	x24, [x2, #CPU_SPSR_OFFSET(KVM_SPSR_EL1)]
>  
> +	msr_hyp(ELR, x20) 		// pc on return from el2
> +	msr_hyp(SPSR, x21) 		// pstate on return from el2
> +
>  	msr	sp_el1, x22
> -	msr	elr_el1, x23
> -	msr	spsr_el1, x24
>  
> -	add	x3, x2, #CPU_XREG_OFFSET(31)    // SP_EL0
> -	ldp	x19, x20, [x3]
> -	ldr	x21, [x3, #16]
> +	msr_el1(elr, x23)
> +	msr_el1(spsr, x24)
> +.endm
>  
> +.macro restore_common_regs
> +	// x2: base address for cpu context
> +	// x3: tmp register
> +
> +	ldr	x19, [x2, #CPU_XREG_OFFSET(31)] // SP_EL0
>  	msr	sp_el0, x19
> -	msr	elr_el2, x20 		// pc on return from el2
> -	msr	spsr_el2, x21 		// pstate on return from el2
>  
>  	add	x3, x2, #CPU_XREG_OFFSET(19)
>  	ldp	x19, x20, [x3]
> @@ -113,9 +125,15 @@
>  
>  .macro save_host_regs
>  	save_common_regs
> +ifnvhe	nop,					"b	skip_el1_save"
> +	save_el1_state
> +skip_el1_save:
>  .endm
>  
>  .macro restore_host_regs
> +ifnvhe	nop,					"b	skip_el1_restore"
> +	restore_el1_state
> +skip_el1_restore:
>  	restore_common_regs
>  .endm
>  
> @@ -159,6 +177,7 @@
>  	stp	x6, x7, [x3, #16]
>  
>  	save_common_regs
> +	save_el1_state
>  .endm
>  
>  .macro restore_guest_regs
> @@ -184,6 +203,7 @@
>  	ldr	x18, [x3, #144]
>  
>  	// x19-x29, lr, sp*, elr*, spsr*
> +	restore_el1_state
>  	restore_common_regs
>  
>  	// Last bits of the 64bit state
> @@ -203,6 +223,38 @@
>   * In other words, don't touch any of these unless you know what
>   * you are doing.
>   */
> +
> +.macro save_shared_sysregs
> +	// x2: base address for cpu context
> +	// x3: tmp register
> +
> +	add	x3, x2, #CPU_SYSREG_OFFSET(TPIDR_EL0)
> +
> +	mrs	x4, tpidr_el0
> +	mrs	x5, tpidrro_el0
> +	mrs	x6, tpidr_el1
> +	mrs	x7, actlr_el1
> +
> +	stp	x4, x5, [x3]
> +	stp	x6, x7, [x3, #16]
> +.endm
> +
> +.macro restore_shared_sysregs
> +	// x2: base address for cpu context
> +	// x3: tmp register
> +
> +	add	x3, x2, #CPU_SYSREG_OFFSET(TPIDR_EL0)
> +
> +	ldp	x4, x5, [x3]
> +	ldp	x6, x7, [x3, #16]
> +
> +	msr	tpidr_el0,      x4
> +	msr	tpidrro_el0,    x5
> +	msr	tpidr_el1,      x6
> +	msr	actlr_el1,      x7
> +.endm
> +
> +
>  .macro save_sysregs
>  	// x2: base address for cpu context
>  	// x3: tmp register
> @@ -211,26 +263,27 @@
>  
>  	mrs	x4,	vmpidr_el2
>  	mrs	x5,	csselr_el1
> -	mrs	x6,	sctlr_el1
> -	mrs	x7,	actlr_el1
> -	mrs	x8,	cpacr_el1
> -	mrs	x9,	ttbr0_el1
> -	mrs	x10,	ttbr1_el1
> -	mrs	x11,	tcr_el1
> -	mrs	x12,	esr_el1
> -	mrs	x13, 	afsr0_el1
> -	mrs	x14,	afsr1_el1
> -	mrs	x15,	far_el1
> -	mrs	x16,	mair_el1
> -	mrs	x17,	vbar_el1
> -	mrs	x18,	contextidr_el1
> -	mrs	x19,	tpidr_el0
> -	mrs	x20,	tpidrro_el0
> -	mrs	x21,	tpidr_el1
> -	mrs	x22, 	amair_el1
> -	mrs	x23, 	cntkctl_el1
> -	mrs	x24,	par_el1
> -	mrs	x25,	mdscr_el1
> +	mrs_el1(x6,	sctlr)
> +	mrs_el1(x7, 	amair)
> +	mrs_el1(x8,	cpacr)
> +	mrs_el1(x9,	ttbr0)
> +	mrs_el1(x10,	ttbr1)
> +	mrs_el1(x11,	tcr)
> +	mrs_el1(x12,	esr)
> +	mrs_el1(x13, 	afsr0)
> +	mrs_el1(x14,	afsr1)
> +	mrs_el1(x15,	far)
> +	mrs_el1(x16,	mair)
> +	mrs_el1(x17,	vbar)
> +	mrs_el1(x18,	contextidr)
> +	mrs_el1(x19, 	cntkctl)
> +	mrs	x20,	par_el1
> +	mrs	x21,	mdscr_el1
> +
> +	mrs	x22,	tpidr_el0
> +	mrs	x23,	tpidrro_el0
> +	mrs	x24,	tpidr_el1
> +	mrs	x25,	actlr_el1
>  
>  	stp	x4, x5, [x3]
>  	stp	x6, x7, [x3, #16]
> @@ -460,26 +513,27 @@
>  
>  	msr	vmpidr_el2,	x4
>  	msr	csselr_el1,	x5
> -	msr	sctlr_el1,	x6
> -	msr	actlr_el1,	x7
> -	msr	cpacr_el1,	x8
> -	msr	ttbr0_el1,	x9
> -	msr	ttbr1_el1,	x10
> -	msr	tcr_el1,	x11
> -	msr	esr_el1,	x12
> -	msr	afsr0_el1,	x13
> -	msr	afsr1_el1,	x14
> -	msr	far_el1,	x15
> -	msr	mair_el1,	x16
> -	msr	vbar_el1,	x17
> -	msr	contextidr_el1,	x18
> -	msr	tpidr_el0,	x19
> -	msr	tpidrro_el0,	x20
> -	msr	tpidr_el1,	x21
> -	msr	amair_el1,	x22
> -	msr	cntkctl_el1,	x23
> -	msr	par_el1,	x24
> -	msr	mdscr_el1,	x25
> +	msr_el1(sctlr,		x6)
> +	msr_el1(amair,		x7)
> +	msr_el1(cpacr,		x8)
> +	msr_el1(ttbr0,		x9)
> +	msr_el1(ttbr1,		x10)
> +	msr_el1(tcr,		x11)
> +	msr_el1(esr,		x12)
> +	msr_el1(afsr0,		x13)
> +	msr_el1(afsr1,		x14)
> +	msr_el1(far,		x15)
> +	msr_el1(mair,		x16)
> +	msr_el1(vbar,		x17)
> +	msr_el1(contextidr,	x18)
> +	msr_el1(cntkctl,	x19)
> +	msr	par_el1,	x20
> +	msr	mdscr_el1,	x21
> +
> +	msr	tpidr_el0,	x22
> +	msr	tpidrro_el0,	x23
> +	msr	tpidr_el1,	x24
> +	msr	actlr_el1,	x25
>  .endm
>  
>  .macro restore_debug
> @@ -779,8 +833,11 @@
>  .macro activate_traps
>  	ldr     x2, [x0, #VCPU_HCR_EL2]
>  	msr     hcr_el2, x2
> -	mov	x2, #CPTR_EL2_TTA
> -	msr	cptr_el2, x2
> +	adr	x3, __kvm_hyp_vector
> +ifnvhe	nop,					"msr	vbar_el1, x3"
> +ifnvhe	nop,					"mrs	x2, cpacr_el1"
> +ifnvhe _S_(ldr	x2, =(CPTR_EL2_TTA)),		"orr x2, x2, #(1 << 28)"
> +ifnvhe "msr	cptr_el2, x2",			"msr	cpacr_el1, x2"
>  
>  	mov	x2, #(1 << 15)	// Trap CP15 Cr=15
>  	msr	hstr_el2, x2
> @@ -803,12 +860,20 @@
>  ifnvhe _S_(mov	x2, #HCR_RW),			_S_(mov	x2, #HCR_RW|HCR_TGE)
>  ifnvhe 	nop,					_S_(orr	x2, x2, #HCR_E2H)
>  	msr	hcr_el2, x2
> -	msr	cptr_el2, xzr
> +
> +ifnvhe	nop,					"mrs	x2, cpacr_el1"
> +ifnvhe	nop,					"movn	x3, #(1 << 12), lsl #16"
> +ifnvhe	nop,					"and	x2, x2, x3"
> +ifnvhe "msr	cptr_el2, xzr",			"msr	cpacr_el1, x2"
>  	msr	hstr_el2, xzr
>  
>  	mrs	x2, mdcr_el2
>  	and	x2, x2, #MDCR_EL2_HPMN_MASK
>  	msr	mdcr_el2, x2
> +
> +	adrp	x2, vectors
> +	add	x2, x2, #:lo12:vectors
> +ifnvhe	nop,					"msr	vbar_el1, x2"
>  .endm
>  
>  .macro activate_vm
> @@ -853,15 +918,15 @@ ifnvhe 	nop,					_S_(orr	x2, x2, #HCR_E2H)
>  	ldr	w3, [x2, #KVM_TIMER_ENABLED]
>  	cbz	w3, 1f
>  
> -	mrs	x3, cntv_ctl_el0
> +	mrs_el0(x3, cntv_ctl)
>  	and	x3, x3, #3
>  	str	w3, [x0, #VCPU_TIMER_CNTV_CTL]
>  	bic	x3, x3, #1		// Clear Enable
> -	msr	cntv_ctl_el0, x3
> +	msr_el0(cntv_ctl, x3)
>  
>  	isb
>  
> -	mrs	x3, cntv_cval_el0
> +	mrs_el0(x3, cntv_cval)
>  	str	x3, [x0, #VCPU_TIMER_CNTV_CVAL]
>  
>  1:
> @@ -871,7 +936,7 @@ ifnvhe 	nop,					_S_(orr	x2, x2, #HCR_E2H)
>  	msr	cnthctl_el2, x2
>  
>  	// Clear cntvoff for the host
> -	msr	cntvoff_el2, xzr
> +ifnvhe "msr	cntvoff_el2, xzr",		nop
>  .endm
>  
>  .macro restore_timer_state
> @@ -891,12 +956,12 @@ ifnvhe 	nop,					_S_(orr	x2, x2, #HCR_E2H)
>  	ldr	x3, [x2, #KVM_TIMER_CNTVOFF]
>  	msr	cntvoff_el2, x3
>  	ldr	x2, [x0, #VCPU_TIMER_CNTV_CVAL]
> -	msr	cntv_cval_el0, x2
> +	msr_el0(cntv_cval, x2)
>  	isb
>  
>  	ldr	w2, [x0, #VCPU_TIMER_CNTV_CTL]
>  	and	x2, x2, #3
> -	msr	cntv_ctl_el0, x2
> +	msr_el0(cntv_ctl, x2)
>  1:
>  .endm
>  
> @@ -945,8 +1010,10 @@ ENTRY(__kvm_vcpu_run)
>  
>  	save_host_regs
>  	bl __save_fpsimd
> -	bl __save_sysregs
> -
> +ifnvhe "bl	__save_sysregs",		nop
> +ifnvhe "b	1f",				nop
> +	save_shared_sysregs
> +1:
>  	compute_debug_state 1f
>  	bl	__save_debug
>  1:
> @@ -997,7 +1064,10 @@ __kvm_vcpu_return:
>  	ldr	x2, [x0, #VCPU_HOST_CONTEXT]
>  	kern_hyp_va x2
>  
> -	bl __restore_sysregs
> +ifnvhe "bl	__restore_sysregs",		nop
> +ifnvhe "b	1f",				nop
> +	restore_shared_sysregs
> +1:
>  	bl __restore_fpsimd
>  
>  	skip_debug_state x3, 1f
> @@ -1104,6 +1174,8 @@ __kvm_hyp_panic:
>  	mrs	x6, par_el1
>  	mrs	x7, tpidr_el2
>  
> +ifnvhe	nop,					"b	panic"
> +
>  	mov	lr, #(PSR_F_BIT | PSR_I_BIT | PSR_A_BIT | PSR_D_BIT |\
>  		      PSR_MODE_EL1h)
>  	msr	spsr_el2, lr
> @@ -1248,7 +1320,7 @@ el1_trap:
>  	 * As such, we can use the EL1 translation regime, and don't have
>  	 * to distinguish between EL0 and EL1 access.
>  	 */
> -	mrs	x2, far_el2
> +ifnvhe "mrs	x2, far_el2",			"mrs	x2, far_el1"
>  	at	s1e1r, x2
>  	isb
>  
> @@ -1262,7 +1334,7 @@ el1_trap:
>  	b	2f
>  
>  1:	mrs	x3, hpfar_el2
> -	mrs	x2, far_el2
> +ifnvhe "mrs	x2, far_el2",			"mrs	x2, far_el1"
>  
>  2:	mrs	x0, tpidr_el2
>  	str	w1, [x0, #VCPU_ESR_EL2]
> diff --git a/arch/arm64/kvm/vhe-macros.h b/arch/arm64/kvm/vhe-macros.h
> index da7f9da..1e94235 100644
> --- a/arch/arm64/kvm/vhe-macros.h
> +++ b/arch/arm64/kvm/vhe-macros.h
> @@ -31,6 +31,24 @@
>  	alternative_insn	"\nonvhe", "\vhe", ARM64_HAS_VIRT_HOST_EXTN
>  .endm
>  
> +#define mrs_el0(reg, sysreg)	\
> +	ifnvhe  _S_(mrs reg, sysreg##_EL0), _S_(mrs_s reg, sysreg##_EL02)
> +
> +#define msr_el0(sysreg, reg)	\
> +	ifnvhe  _S_(msr sysreg##_EL0, reg), _S_(msr_s sysreg##_EL02, reg)
> +
> +#define mrs_el1(reg, sysreg)	\
> +	ifnvhe  _S_(mrs reg, sysreg##_EL1), _S_(mrs_s reg, sysreg##_EL12)
> +
> +#define msr_el1(sysreg, reg)	\
> +	ifnvhe  _S_(msr sysreg##_EL1, reg), _S_(msr_s sysreg##_EL12, reg)
> +
> +#define mrs_hyp(reg, sysreg)	\
> +	ifnvhe  _S_(mrs reg, sysreg##_EL2), _S_(mrs reg, sysreg##_EL1)
> +
> +#define msr_hyp(sysreg, reg)	\
> +	ifnvhe  _S_(msr sysreg##_EL2, reg), _S_(msr sysreg##_EL1, reg)
> +
>  #endif
>  
>  #endif	/*__ARM64_VHE_MACROS_H__  */
> 

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