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* [PATCH v2] arm64: KVM: Save four instructions in __guest_enter/exit()
@ 2016-08-30  3:51 ` Shanker Donthineni
  0 siblings, 0 replies; 10+ messages in thread
From: Shanker Donthineni @ 2016-08-30  3:51 UTC (permalink / raw)
  To: Marc Zyngier, Christoffer Dall, linux-kernel, linux-arm-kernel, kvmarm
  Cc: Paolo Bonzini, Will Deacon, Catalin Marinas, James Morse,
	Shanker Donthineni

We are doing an unnecessary stack push/pop operation when restoring
the guest registers x0-x18 in __guest_enter(). This patch saves the
two instructions by using x18 as a base register. No need to store
the vcpu context pointer in stack because it is redundant, the same
information is available in tpidr_el2. The function __guest_exit()
prototype is simplified and caller pushes the regs x0-x1 to stack
instead of regs x0-x3.

Signed-off-by: Shanker Donthineni <shankerd@codeaurora.org>
---
Changes since v1:
  Incorporated Cristoffer suggestions.
  __guest_exit prototype is changed to 'void __guest_exit(u64 reason, struct kvm_vcpu *vcpu)'.

 arch/arm64/kvm/hyp/entry.S     | 101 +++++++++++++++++++++--------------------
 arch/arm64/kvm/hyp/hyp-entry.S |  11 +++--
 2 files changed, 57 insertions(+), 55 deletions(-)

diff --git a/arch/arm64/kvm/hyp/entry.S b/arch/arm64/kvm/hyp/entry.S
index ce9e5e5..f70489a 100644
--- a/arch/arm64/kvm/hyp/entry.S
+++ b/arch/arm64/kvm/hyp/entry.S
@@ -55,75 +55,76 @@
  */
 ENTRY(__guest_enter)
 	// x0: vcpu
-	// x1: host/guest context
-	// x2-x18: clobbered by macros
+	// x1: host context
+	// x2-x17: clobbered by macros
+	// x18: guest context
 
 	// Store the host regs
 	save_callee_saved_regs x1
 
-	// Preserve vcpu & host_ctxt for use at exit time
-	stp	x0, x1, [sp, #-16]!
+	// Store the host_ctxt for use at exit time
+	str	x1, [sp, #-16]!
 
-	add	x1, x0, #VCPU_CONTEXT
+	add	x18, x0, #VCPU_CONTEXT
 
-	// Prepare x0-x1 for later restore by pushing them onto the stack
-	ldp	x2, x3, [x1, #CPU_XREG_OFFSET(0)]
-	stp	x2, x3, [sp, #-16]!
+	// Restore guest regs x0-x17
+	ldp	x0, x1,   [x18, #CPU_XREG_OFFSET(0)]
+	ldp	x2, x3,   [x18, #CPU_XREG_OFFSET(2)]
+	ldp	x4, x5,   [x18, #CPU_XREG_OFFSET(4)]
+	ldp	x6, x7,   [x18, #CPU_XREG_OFFSET(6)]
+	ldp	x8, x9,   [x18, #CPU_XREG_OFFSET(8)]
+	ldp	x10, x11, [x18, #CPU_XREG_OFFSET(10)]
+	ldp	x12, x13, [x18, #CPU_XREG_OFFSET(12)]
+	ldp	x14, x15, [x18, #CPU_XREG_OFFSET(14)]
+	ldp	x16, x17, [x18, #CPU_XREG_OFFSET(16)]
 
-	// x2-x18
-	ldp	x2, x3,   [x1, #CPU_XREG_OFFSET(2)]
-	ldp	x4, x5,   [x1, #CPU_XREG_OFFSET(4)]
-	ldp	x6, x7,   [x1, #CPU_XREG_OFFSET(6)]
-	ldp	x8, x9,   [x1, #CPU_XREG_OFFSET(8)]
-	ldp	x10, x11, [x1, #CPU_XREG_OFFSET(10)]
-	ldp	x12, x13, [x1, #CPU_XREG_OFFSET(12)]
-	ldp	x14, x15, [x1, #CPU_XREG_OFFSET(14)]
-	ldp	x16, x17, [x1, #CPU_XREG_OFFSET(16)]
-	ldr	x18,      [x1, #CPU_XREG_OFFSET(18)]
+	// Restore guest regs x19-x29, lr
+	restore_callee_saved_regs x18
 
-	// x19-x29, lr
-	restore_callee_saved_regs x1
-
-	// Last bits of the 64bit state
-	ldp	x0, x1, [sp], #16
+	// Restore guest reg x18
+	ldr	x18,      [x18, #CPU_XREG_OFFSET(18)]
 
 	// Do not touch any register after this!
 	eret
 ENDPROC(__guest_enter)
 
+/*
+ * void __guest_exit(u64 exit_reason, struct kvm_vcpu *vcpu);
+ */
 ENTRY(__guest_exit)
-	// x0: vcpu
-	// x1: return code
-	// x2-x3: free
-	// x4-x29,lr: vcpu regs
-	// vcpu x0-x3 on the stack
-
-	add	x2, x0, #VCPU_CONTEXT
-
-	stp	x4, x5,   [x2, #CPU_XREG_OFFSET(4)]
-	stp	x6, x7,   [x2, #CPU_XREG_OFFSET(6)]
-	stp	x8, x9,   [x2, #CPU_XREG_OFFSET(8)]
-	stp	x10, x11, [x2, #CPU_XREG_OFFSET(10)]
-	stp	x12, x13, [x2, #CPU_XREG_OFFSET(12)]
-	stp	x14, x15, [x2, #CPU_XREG_OFFSET(14)]
-	stp	x16, x17, [x2, #CPU_XREG_OFFSET(16)]
-	str	x18,      [x2, #CPU_XREG_OFFSET(18)]
-
-	ldp	x6, x7, [sp], #16	// x2, x3
-	ldp	x4, x5, [sp], #16	// x0, x1
-
-	stp	x4, x5, [x2, #CPU_XREG_OFFSET(0)]
-	stp	x6, x7, [x2, #CPU_XREG_OFFSET(2)]
+	// x0: return code
+	// x1: vcpu
+	// x2-x29,lr: vcpu regs
+	// vcpu x0-x1 on the stack
+
+	add	x1, x1, #VCPU_CONTEXT
+
+	// Store the guest regs x2 and x3
+	stp	x2, x3,   [x1, #CPU_XREG_OFFSET(2)]
+
+	// Retrieve the guest regs x0-x1 from the stack
+	ldp	x2, x3, [sp], #16	// x0, x1
+
+	// Store the guest regs x0-x1 and x4-x18
+	stp	x2, x3,   [x1, #CPU_XREG_OFFSET(0)]
+	stp	x4, x5,   [x1, #CPU_XREG_OFFSET(4)]
+	stp	x6, x7,   [x1, #CPU_XREG_OFFSET(6)]
+	stp	x8, x9,   [x1, #CPU_XREG_OFFSET(8)]
+	stp	x10, x11, [x1, #CPU_XREG_OFFSET(10)]
+	stp	x12, x13, [x1, #CPU_XREG_OFFSET(12)]
+	stp	x14, x15, [x1, #CPU_XREG_OFFSET(14)]
+	stp	x16, x17, [x1, #CPU_XREG_OFFSET(16)]
+	str	x18,      [x1, #CPU_XREG_OFFSET(18)]
+
+	// Store the guest regs x19-x29, lr
+	save_callee_saved_regs x1
 
-	save_callee_saved_regs x2
+	// Restore the host_ctxt from the stack
+	ldr	x2, [sp], #16
 
-	// Restore vcpu & host_ctxt from the stack
-	// (preserving return code in x1)
-	ldp	x0, x2, [sp], #16
 	// Now restore the host regs
 	restore_callee_saved_regs x2
 
-	mov	x0, x1
 	ret
 ENDPROC(__guest_exit)
 
diff --git a/arch/arm64/kvm/hyp/hyp-entry.S b/arch/arm64/kvm/hyp/hyp-entry.S
index f6d9694..06e8b3b 100644
--- a/arch/arm64/kvm/hyp/hyp-entry.S
+++ b/arch/arm64/kvm/hyp/hyp-entry.S
@@ -121,14 +121,15 @@ el1_trap:
 	cmp	x2, #ESR_ELx_EC_FP_ASIMD
 	b.eq	__fpsimd_guest_restore
 
-	mrs	x0, tpidr_el2
-	mov	x1, #ARM_EXCEPTION_TRAP
+	ldp     x2, x3, [sp], #16
+	mrs	x1, tpidr_el2
+	mov	x0, #ARM_EXCEPTION_TRAP
 	b	__guest_exit
 
 el1_irq:
-	save_x0_to_x3
-	mrs	x0, tpidr_el2
-	mov	x1, #ARM_EXCEPTION_IRQ
+	stp     x0, x1, [sp, #-16]!
+	mrs	x1, tpidr_el2
+	mov	x0, #ARM_EXCEPTION_IRQ
 	b	__guest_exit
 
 ENTRY(__hyp_do_panic)
-- 
Qualcomm Datacenter Technologies, Inc. on behalf of the Qualcomm Technologies, Inc.
Qualcomm Technologies, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project.

^ permalink raw reply related	[flat|nested] 10+ messages in thread

* [PATCH v2] arm64: KVM: Save four instructions in __guest_enter/exit()
@ 2016-08-30  3:51 ` Shanker Donthineni
  0 siblings, 0 replies; 10+ messages in thread
From: Shanker Donthineni @ 2016-08-30  3:51 UTC (permalink / raw)
  To: linux-arm-kernel

We are doing an unnecessary stack push/pop operation when restoring
the guest registers x0-x18 in __guest_enter(). This patch saves the
two instructions by using x18 as a base register. No need to store
the vcpu context pointer in stack because it is redundant, the same
information is available in tpidr_el2. The function __guest_exit()
prototype is simplified and caller pushes the regs x0-x1 to stack
instead of regs x0-x3.

Signed-off-by: Shanker Donthineni <shankerd@codeaurora.org>
---
Changes since v1:
  Incorporated Cristoffer suggestions.
  __guest_exit prototype is changed to 'void __guest_exit(u64 reason, struct kvm_vcpu *vcpu)'.

 arch/arm64/kvm/hyp/entry.S     | 101 +++++++++++++++++++++--------------------
 arch/arm64/kvm/hyp/hyp-entry.S |  11 +++--
 2 files changed, 57 insertions(+), 55 deletions(-)

diff --git a/arch/arm64/kvm/hyp/entry.S b/arch/arm64/kvm/hyp/entry.S
index ce9e5e5..f70489a 100644
--- a/arch/arm64/kvm/hyp/entry.S
+++ b/arch/arm64/kvm/hyp/entry.S
@@ -55,75 +55,76 @@
  */
 ENTRY(__guest_enter)
 	// x0: vcpu
-	// x1: host/guest context
-	// x2-x18: clobbered by macros
+	// x1: host context
+	// x2-x17: clobbered by macros
+	// x18: guest context
 
 	// Store the host regs
 	save_callee_saved_regs x1
 
-	// Preserve vcpu & host_ctxt for use at exit time
-	stp	x0, x1, [sp, #-16]!
+	// Store the host_ctxt for use at exit time
+	str	x1, [sp, #-16]!
 
-	add	x1, x0, #VCPU_CONTEXT
+	add	x18, x0, #VCPU_CONTEXT
 
-	// Prepare x0-x1 for later restore by pushing them onto the stack
-	ldp	x2, x3, [x1, #CPU_XREG_OFFSET(0)]
-	stp	x2, x3, [sp, #-16]!
+	// Restore guest regs x0-x17
+	ldp	x0, x1,   [x18, #CPU_XREG_OFFSET(0)]
+	ldp	x2, x3,   [x18, #CPU_XREG_OFFSET(2)]
+	ldp	x4, x5,   [x18, #CPU_XREG_OFFSET(4)]
+	ldp	x6, x7,   [x18, #CPU_XREG_OFFSET(6)]
+	ldp	x8, x9,   [x18, #CPU_XREG_OFFSET(8)]
+	ldp	x10, x11, [x18, #CPU_XREG_OFFSET(10)]
+	ldp	x12, x13, [x18, #CPU_XREG_OFFSET(12)]
+	ldp	x14, x15, [x18, #CPU_XREG_OFFSET(14)]
+	ldp	x16, x17, [x18, #CPU_XREG_OFFSET(16)]
 
-	// x2-x18
-	ldp	x2, x3,   [x1, #CPU_XREG_OFFSET(2)]
-	ldp	x4, x5,   [x1, #CPU_XREG_OFFSET(4)]
-	ldp	x6, x7,   [x1, #CPU_XREG_OFFSET(6)]
-	ldp	x8, x9,   [x1, #CPU_XREG_OFFSET(8)]
-	ldp	x10, x11, [x1, #CPU_XREG_OFFSET(10)]
-	ldp	x12, x13, [x1, #CPU_XREG_OFFSET(12)]
-	ldp	x14, x15, [x1, #CPU_XREG_OFFSET(14)]
-	ldp	x16, x17, [x1, #CPU_XREG_OFFSET(16)]
-	ldr	x18,      [x1, #CPU_XREG_OFFSET(18)]
+	// Restore guest regs x19-x29, lr
+	restore_callee_saved_regs x18
 
-	// x19-x29, lr
-	restore_callee_saved_regs x1
-
-	// Last bits of the 64bit state
-	ldp	x0, x1, [sp], #16
+	// Restore guest reg x18
+	ldr	x18,      [x18, #CPU_XREG_OFFSET(18)]
 
 	// Do not touch any register after this!
 	eret
 ENDPROC(__guest_enter)
 
+/*
+ * void __guest_exit(u64 exit_reason, struct kvm_vcpu *vcpu);
+ */
 ENTRY(__guest_exit)
-	// x0: vcpu
-	// x1: return code
-	// x2-x3: free
-	// x4-x29,lr: vcpu regs
-	// vcpu x0-x3 on the stack
-
-	add	x2, x0, #VCPU_CONTEXT
-
-	stp	x4, x5,   [x2, #CPU_XREG_OFFSET(4)]
-	stp	x6, x7,   [x2, #CPU_XREG_OFFSET(6)]
-	stp	x8, x9,   [x2, #CPU_XREG_OFFSET(8)]
-	stp	x10, x11, [x2, #CPU_XREG_OFFSET(10)]
-	stp	x12, x13, [x2, #CPU_XREG_OFFSET(12)]
-	stp	x14, x15, [x2, #CPU_XREG_OFFSET(14)]
-	stp	x16, x17, [x2, #CPU_XREG_OFFSET(16)]
-	str	x18,      [x2, #CPU_XREG_OFFSET(18)]
-
-	ldp	x6, x7, [sp], #16	// x2, x3
-	ldp	x4, x5, [sp], #16	// x0, x1
-
-	stp	x4, x5, [x2, #CPU_XREG_OFFSET(0)]
-	stp	x6, x7, [x2, #CPU_XREG_OFFSET(2)]
+	// x0: return code
+	// x1: vcpu
+	// x2-x29,lr: vcpu regs
+	// vcpu x0-x1 on the stack
+
+	add	x1, x1, #VCPU_CONTEXT
+
+	// Store the guest regs x2 and x3
+	stp	x2, x3,   [x1, #CPU_XREG_OFFSET(2)]
+
+	// Retrieve the guest regs x0-x1 from the stack
+	ldp	x2, x3, [sp], #16	// x0, x1
+
+	// Store the guest regs x0-x1 and x4-x18
+	stp	x2, x3,   [x1, #CPU_XREG_OFFSET(0)]
+	stp	x4, x5,   [x1, #CPU_XREG_OFFSET(4)]
+	stp	x6, x7,   [x1, #CPU_XREG_OFFSET(6)]
+	stp	x8, x9,   [x1, #CPU_XREG_OFFSET(8)]
+	stp	x10, x11, [x1, #CPU_XREG_OFFSET(10)]
+	stp	x12, x13, [x1, #CPU_XREG_OFFSET(12)]
+	stp	x14, x15, [x1, #CPU_XREG_OFFSET(14)]
+	stp	x16, x17, [x1, #CPU_XREG_OFFSET(16)]
+	str	x18,      [x1, #CPU_XREG_OFFSET(18)]
+
+	// Store the guest regs x19-x29, lr
+	save_callee_saved_regs x1
 
-	save_callee_saved_regs x2
+	// Restore the host_ctxt from the stack
+	ldr	x2, [sp], #16
 
-	// Restore vcpu & host_ctxt from the stack
-	// (preserving return code in x1)
-	ldp	x0, x2, [sp], #16
 	// Now restore the host regs
 	restore_callee_saved_regs x2
 
-	mov	x0, x1
 	ret
 ENDPROC(__guest_exit)
 
diff --git a/arch/arm64/kvm/hyp/hyp-entry.S b/arch/arm64/kvm/hyp/hyp-entry.S
index f6d9694..06e8b3b 100644
--- a/arch/arm64/kvm/hyp/hyp-entry.S
+++ b/arch/arm64/kvm/hyp/hyp-entry.S
@@ -121,14 +121,15 @@ el1_trap:
 	cmp	x2, #ESR_ELx_EC_FP_ASIMD
 	b.eq	__fpsimd_guest_restore
 
-	mrs	x0, tpidr_el2
-	mov	x1, #ARM_EXCEPTION_TRAP
+	ldp     x2, x3, [sp], #16
+	mrs	x1, tpidr_el2
+	mov	x0, #ARM_EXCEPTION_TRAP
 	b	__guest_exit
 
 el1_irq:
-	save_x0_to_x3
-	mrs	x0, tpidr_el2
-	mov	x1, #ARM_EXCEPTION_IRQ
+	stp     x0, x1, [sp, #-16]!
+	mrs	x1, tpidr_el2
+	mov	x0, #ARM_EXCEPTION_IRQ
 	b	__guest_exit
 
 ENTRY(__hyp_do_panic)
-- 
Qualcomm Datacenter Technologies, Inc. on behalf of the Qualcomm Technologies, Inc.
Qualcomm Technologies, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project.

^ permalink raw reply related	[flat|nested] 10+ messages in thread

* Re: [PATCH v2] arm64: KVM: Save four instructions in __guest_enter/exit()
  2016-08-30  3:51 ` Shanker Donthineni
  (?)
@ 2016-08-30  9:55   ` Christoffer Dall
  -1 siblings, 0 replies; 10+ messages in thread
From: Christoffer Dall @ 2016-08-30  9:55 UTC (permalink / raw)
  To: Shanker Donthineni
  Cc: Marc Zyngier, linux-kernel, linux-arm-kernel, kvmarm,
	Paolo Bonzini, Will Deacon, Catalin Marinas, James Morse

On Mon, Aug 29, 2016 at 10:51:14PM -0500, Shanker Donthineni wrote:
> We are doing an unnecessary stack push/pop operation when restoring
> the guest registers x0-x18 in __guest_enter(). This patch saves the
> two instructions by using x18 as a base register. No need to store
> the vcpu context pointer in stack because it is redundant, the same
> information is available in tpidr_el2. The function __guest_exit()
> prototype is simplified and caller pushes the regs x0-x1 to stack
> instead of regs x0-x3.
> 
> Signed-off-by: Shanker Donthineni <shankerd@codeaurora.org>

This looks reasonable to me:

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

Unless Marc has any insight into this having a negative effect on ARM
CPUs, I'll go ahead an merge this.

-Christoffer

> ---
> Changes since v1:
>   Incorporated Cristoffer suggestions.
>   __guest_exit prototype is changed to 'void __guest_exit(u64 reason, struct kvm_vcpu *vcpu)'.
> 
>  arch/arm64/kvm/hyp/entry.S     | 101 +++++++++++++++++++++--------------------
>  arch/arm64/kvm/hyp/hyp-entry.S |  11 +++--
>  2 files changed, 57 insertions(+), 55 deletions(-)
> 
> diff --git a/arch/arm64/kvm/hyp/entry.S b/arch/arm64/kvm/hyp/entry.S
> index ce9e5e5..f70489a 100644
> --- a/arch/arm64/kvm/hyp/entry.S
> +++ b/arch/arm64/kvm/hyp/entry.S
> @@ -55,75 +55,76 @@
>   */
>  ENTRY(__guest_enter)
>  	// x0: vcpu
> -	// x1: host/guest context
> -	// x2-x18: clobbered by macros
> +	// x1: host context
> +	// x2-x17: clobbered by macros
> +	// x18: guest context
>  
>  	// Store the host regs
>  	save_callee_saved_regs x1
>  
> -	// Preserve vcpu & host_ctxt for use at exit time
> -	stp	x0, x1, [sp, #-16]!
> +	// Store the host_ctxt for use at exit time
> +	str	x1, [sp, #-16]!
>  
> -	add	x1, x0, #VCPU_CONTEXT
> +	add	x18, x0, #VCPU_CONTEXT
>  
> -	// Prepare x0-x1 for later restore by pushing them onto the stack
> -	ldp	x2, x3, [x1, #CPU_XREG_OFFSET(0)]
> -	stp	x2, x3, [sp, #-16]!
> +	// Restore guest regs x0-x17
> +	ldp	x0, x1,   [x18, #CPU_XREG_OFFSET(0)]
> +	ldp	x2, x3,   [x18, #CPU_XREG_OFFSET(2)]
> +	ldp	x4, x5,   [x18, #CPU_XREG_OFFSET(4)]
> +	ldp	x6, x7,   [x18, #CPU_XREG_OFFSET(6)]
> +	ldp	x8, x9,   [x18, #CPU_XREG_OFFSET(8)]
> +	ldp	x10, x11, [x18, #CPU_XREG_OFFSET(10)]
> +	ldp	x12, x13, [x18, #CPU_XREG_OFFSET(12)]
> +	ldp	x14, x15, [x18, #CPU_XREG_OFFSET(14)]
> +	ldp	x16, x17, [x18, #CPU_XREG_OFFSET(16)]
>  
> -	// x2-x18
> -	ldp	x2, x3,   [x1, #CPU_XREG_OFFSET(2)]
> -	ldp	x4, x5,   [x1, #CPU_XREG_OFFSET(4)]
> -	ldp	x6, x7,   [x1, #CPU_XREG_OFFSET(6)]
> -	ldp	x8, x9,   [x1, #CPU_XREG_OFFSET(8)]
> -	ldp	x10, x11, [x1, #CPU_XREG_OFFSET(10)]
> -	ldp	x12, x13, [x1, #CPU_XREG_OFFSET(12)]
> -	ldp	x14, x15, [x1, #CPU_XREG_OFFSET(14)]
> -	ldp	x16, x17, [x1, #CPU_XREG_OFFSET(16)]
> -	ldr	x18,      [x1, #CPU_XREG_OFFSET(18)]
> +	// Restore guest regs x19-x29, lr
> +	restore_callee_saved_regs x18
>  
> -	// x19-x29, lr
> -	restore_callee_saved_regs x1
> -
> -	// Last bits of the 64bit state
> -	ldp	x0, x1, [sp], #16
> +	// Restore guest reg x18
> +	ldr	x18,      [x18, #CPU_XREG_OFFSET(18)]
>  
>  	// Do not touch any register after this!
>  	eret
>  ENDPROC(__guest_enter)
>  
> +/*
> + * void __guest_exit(u64 exit_reason, struct kvm_vcpu *vcpu);
> + */
>  ENTRY(__guest_exit)
> -	// x0: vcpu
> -	// x1: return code
> -	// x2-x3: free
> -	// x4-x29,lr: vcpu regs
> -	// vcpu x0-x3 on the stack
> -
> -	add	x2, x0, #VCPU_CONTEXT
> -
> -	stp	x4, x5,   [x2, #CPU_XREG_OFFSET(4)]
> -	stp	x6, x7,   [x2, #CPU_XREG_OFFSET(6)]
> -	stp	x8, x9,   [x2, #CPU_XREG_OFFSET(8)]
> -	stp	x10, x11, [x2, #CPU_XREG_OFFSET(10)]
> -	stp	x12, x13, [x2, #CPU_XREG_OFFSET(12)]
> -	stp	x14, x15, [x2, #CPU_XREG_OFFSET(14)]
> -	stp	x16, x17, [x2, #CPU_XREG_OFFSET(16)]
> -	str	x18,      [x2, #CPU_XREG_OFFSET(18)]
> -
> -	ldp	x6, x7, [sp], #16	// x2, x3
> -	ldp	x4, x5, [sp], #16	// x0, x1
> -
> -	stp	x4, x5, [x2, #CPU_XREG_OFFSET(0)]
> -	stp	x6, x7, [x2, #CPU_XREG_OFFSET(2)]
> +	// x0: return code
> +	// x1: vcpu
> +	// x2-x29,lr: vcpu regs
> +	// vcpu x0-x1 on the stack
> +
> +	add	x1, x1, #VCPU_CONTEXT
> +
> +	// Store the guest regs x2 and x3
> +	stp	x2, x3,   [x1, #CPU_XREG_OFFSET(2)]
> +
> +	// Retrieve the guest regs x0-x1 from the stack
> +	ldp	x2, x3, [sp], #16	// x0, x1
> +
> +	// Store the guest regs x0-x1 and x4-x18
> +	stp	x2, x3,   [x1, #CPU_XREG_OFFSET(0)]
> +	stp	x4, x5,   [x1, #CPU_XREG_OFFSET(4)]
> +	stp	x6, x7,   [x1, #CPU_XREG_OFFSET(6)]
> +	stp	x8, x9,   [x1, #CPU_XREG_OFFSET(8)]
> +	stp	x10, x11, [x1, #CPU_XREG_OFFSET(10)]
> +	stp	x12, x13, [x1, #CPU_XREG_OFFSET(12)]
> +	stp	x14, x15, [x1, #CPU_XREG_OFFSET(14)]
> +	stp	x16, x17, [x1, #CPU_XREG_OFFSET(16)]
> +	str	x18,      [x1, #CPU_XREG_OFFSET(18)]
> +
> +	// Store the guest regs x19-x29, lr
> +	save_callee_saved_regs x1
>  
> -	save_callee_saved_regs x2
> +	// Restore the host_ctxt from the stack
> +	ldr	x2, [sp], #16
>  
> -	// Restore vcpu & host_ctxt from the stack
> -	// (preserving return code in x1)
> -	ldp	x0, x2, [sp], #16
>  	// Now restore the host regs
>  	restore_callee_saved_regs x2
>  
> -	mov	x0, x1
>  	ret
>  ENDPROC(__guest_exit)
>  
> diff --git a/arch/arm64/kvm/hyp/hyp-entry.S b/arch/arm64/kvm/hyp/hyp-entry.S
> index f6d9694..06e8b3b 100644
> --- a/arch/arm64/kvm/hyp/hyp-entry.S
> +++ b/arch/arm64/kvm/hyp/hyp-entry.S
> @@ -121,14 +121,15 @@ el1_trap:
>  	cmp	x2, #ESR_ELx_EC_FP_ASIMD
>  	b.eq	__fpsimd_guest_restore
>  
> -	mrs	x0, tpidr_el2
> -	mov	x1, #ARM_EXCEPTION_TRAP
> +	ldp     x2, x3, [sp], #16
> +	mrs	x1, tpidr_el2
> +	mov	x0, #ARM_EXCEPTION_TRAP
>  	b	__guest_exit
>  
>  el1_irq:
> -	save_x0_to_x3
> -	mrs	x0, tpidr_el2
> -	mov	x1, #ARM_EXCEPTION_IRQ
> +	stp     x0, x1, [sp, #-16]!
> +	mrs	x1, tpidr_el2
> +	mov	x0, #ARM_EXCEPTION_IRQ
>  	b	__guest_exit
>  
>  ENTRY(__hyp_do_panic)
> -- 
> Qualcomm Datacenter Technologies, Inc. on behalf of the Qualcomm Technologies, Inc.
> Qualcomm Technologies, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project.
> 

^ permalink raw reply	[flat|nested] 10+ messages in thread

* Re: [PATCH v2] arm64: KVM: Save four instructions in __guest_enter/exit()
@ 2016-08-30  9:55   ` Christoffer Dall
  0 siblings, 0 replies; 10+ messages in thread
From: Christoffer Dall @ 2016-08-30  9:55 UTC (permalink / raw)
  To: Shanker Donthineni
  Cc: Marc Zyngier, Catalin Marinas, Will Deacon, linux-kernel,
	Paolo Bonzini, kvmarm, linux-arm-kernel

On Mon, Aug 29, 2016 at 10:51:14PM -0500, Shanker Donthineni wrote:
> We are doing an unnecessary stack push/pop operation when restoring
> the guest registers x0-x18 in __guest_enter(). This patch saves the
> two instructions by using x18 as a base register. No need to store
> the vcpu context pointer in stack because it is redundant, the same
> information is available in tpidr_el2. The function __guest_exit()
> prototype is simplified and caller pushes the regs x0-x1 to stack
> instead of regs x0-x3.
> 
> Signed-off-by: Shanker Donthineni <shankerd@codeaurora.org>

This looks reasonable to me:

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

Unless Marc has any insight into this having a negative effect on ARM
CPUs, I'll go ahead an merge this.

-Christoffer

> ---
> Changes since v1:
>   Incorporated Cristoffer suggestions.
>   __guest_exit prototype is changed to 'void __guest_exit(u64 reason, struct kvm_vcpu *vcpu)'.
> 
>  arch/arm64/kvm/hyp/entry.S     | 101 +++++++++++++++++++++--------------------
>  arch/arm64/kvm/hyp/hyp-entry.S |  11 +++--
>  2 files changed, 57 insertions(+), 55 deletions(-)
> 
> diff --git a/arch/arm64/kvm/hyp/entry.S b/arch/arm64/kvm/hyp/entry.S
> index ce9e5e5..f70489a 100644
> --- a/arch/arm64/kvm/hyp/entry.S
> +++ b/arch/arm64/kvm/hyp/entry.S
> @@ -55,75 +55,76 @@
>   */
>  ENTRY(__guest_enter)
>  	// x0: vcpu
> -	// x1: host/guest context
> -	// x2-x18: clobbered by macros
> +	// x1: host context
> +	// x2-x17: clobbered by macros
> +	// x18: guest context
>  
>  	// Store the host regs
>  	save_callee_saved_regs x1
>  
> -	// Preserve vcpu & host_ctxt for use at exit time
> -	stp	x0, x1, [sp, #-16]!
> +	// Store the host_ctxt for use at exit time
> +	str	x1, [sp, #-16]!
>  
> -	add	x1, x0, #VCPU_CONTEXT
> +	add	x18, x0, #VCPU_CONTEXT
>  
> -	// Prepare x0-x1 for later restore by pushing them onto the stack
> -	ldp	x2, x3, [x1, #CPU_XREG_OFFSET(0)]
> -	stp	x2, x3, [sp, #-16]!
> +	// Restore guest regs x0-x17
> +	ldp	x0, x1,   [x18, #CPU_XREG_OFFSET(0)]
> +	ldp	x2, x3,   [x18, #CPU_XREG_OFFSET(2)]
> +	ldp	x4, x5,   [x18, #CPU_XREG_OFFSET(4)]
> +	ldp	x6, x7,   [x18, #CPU_XREG_OFFSET(6)]
> +	ldp	x8, x9,   [x18, #CPU_XREG_OFFSET(8)]
> +	ldp	x10, x11, [x18, #CPU_XREG_OFFSET(10)]
> +	ldp	x12, x13, [x18, #CPU_XREG_OFFSET(12)]
> +	ldp	x14, x15, [x18, #CPU_XREG_OFFSET(14)]
> +	ldp	x16, x17, [x18, #CPU_XREG_OFFSET(16)]
>  
> -	// x2-x18
> -	ldp	x2, x3,   [x1, #CPU_XREG_OFFSET(2)]
> -	ldp	x4, x5,   [x1, #CPU_XREG_OFFSET(4)]
> -	ldp	x6, x7,   [x1, #CPU_XREG_OFFSET(6)]
> -	ldp	x8, x9,   [x1, #CPU_XREG_OFFSET(8)]
> -	ldp	x10, x11, [x1, #CPU_XREG_OFFSET(10)]
> -	ldp	x12, x13, [x1, #CPU_XREG_OFFSET(12)]
> -	ldp	x14, x15, [x1, #CPU_XREG_OFFSET(14)]
> -	ldp	x16, x17, [x1, #CPU_XREG_OFFSET(16)]
> -	ldr	x18,      [x1, #CPU_XREG_OFFSET(18)]
> +	// Restore guest regs x19-x29, lr
> +	restore_callee_saved_regs x18
>  
> -	// x19-x29, lr
> -	restore_callee_saved_regs x1
> -
> -	// Last bits of the 64bit state
> -	ldp	x0, x1, [sp], #16
> +	// Restore guest reg x18
> +	ldr	x18,      [x18, #CPU_XREG_OFFSET(18)]
>  
>  	// Do not touch any register after this!
>  	eret
>  ENDPROC(__guest_enter)
>  
> +/*
> + * void __guest_exit(u64 exit_reason, struct kvm_vcpu *vcpu);
> + */
>  ENTRY(__guest_exit)
> -	// x0: vcpu
> -	// x1: return code
> -	// x2-x3: free
> -	// x4-x29,lr: vcpu regs
> -	// vcpu x0-x3 on the stack
> -
> -	add	x2, x0, #VCPU_CONTEXT
> -
> -	stp	x4, x5,   [x2, #CPU_XREG_OFFSET(4)]
> -	stp	x6, x7,   [x2, #CPU_XREG_OFFSET(6)]
> -	stp	x8, x9,   [x2, #CPU_XREG_OFFSET(8)]
> -	stp	x10, x11, [x2, #CPU_XREG_OFFSET(10)]
> -	stp	x12, x13, [x2, #CPU_XREG_OFFSET(12)]
> -	stp	x14, x15, [x2, #CPU_XREG_OFFSET(14)]
> -	stp	x16, x17, [x2, #CPU_XREG_OFFSET(16)]
> -	str	x18,      [x2, #CPU_XREG_OFFSET(18)]
> -
> -	ldp	x6, x7, [sp], #16	// x2, x3
> -	ldp	x4, x5, [sp], #16	// x0, x1
> -
> -	stp	x4, x5, [x2, #CPU_XREG_OFFSET(0)]
> -	stp	x6, x7, [x2, #CPU_XREG_OFFSET(2)]
> +	// x0: return code
> +	// x1: vcpu
> +	// x2-x29,lr: vcpu regs
> +	// vcpu x0-x1 on the stack
> +
> +	add	x1, x1, #VCPU_CONTEXT
> +
> +	// Store the guest regs x2 and x3
> +	stp	x2, x3,   [x1, #CPU_XREG_OFFSET(2)]
> +
> +	// Retrieve the guest regs x0-x1 from the stack
> +	ldp	x2, x3, [sp], #16	// x0, x1
> +
> +	// Store the guest regs x0-x1 and x4-x18
> +	stp	x2, x3,   [x1, #CPU_XREG_OFFSET(0)]
> +	stp	x4, x5,   [x1, #CPU_XREG_OFFSET(4)]
> +	stp	x6, x7,   [x1, #CPU_XREG_OFFSET(6)]
> +	stp	x8, x9,   [x1, #CPU_XREG_OFFSET(8)]
> +	stp	x10, x11, [x1, #CPU_XREG_OFFSET(10)]
> +	stp	x12, x13, [x1, #CPU_XREG_OFFSET(12)]
> +	stp	x14, x15, [x1, #CPU_XREG_OFFSET(14)]
> +	stp	x16, x17, [x1, #CPU_XREG_OFFSET(16)]
> +	str	x18,      [x1, #CPU_XREG_OFFSET(18)]
> +
> +	// Store the guest regs x19-x29, lr
> +	save_callee_saved_regs x1
>  
> -	save_callee_saved_regs x2
> +	// Restore the host_ctxt from the stack
> +	ldr	x2, [sp], #16
>  
> -	// Restore vcpu & host_ctxt from the stack
> -	// (preserving return code in x1)
> -	ldp	x0, x2, [sp], #16
>  	// Now restore the host regs
>  	restore_callee_saved_regs x2
>  
> -	mov	x0, x1
>  	ret
>  ENDPROC(__guest_exit)
>  
> diff --git a/arch/arm64/kvm/hyp/hyp-entry.S b/arch/arm64/kvm/hyp/hyp-entry.S
> index f6d9694..06e8b3b 100644
> --- a/arch/arm64/kvm/hyp/hyp-entry.S
> +++ b/arch/arm64/kvm/hyp/hyp-entry.S
> @@ -121,14 +121,15 @@ el1_trap:
>  	cmp	x2, #ESR_ELx_EC_FP_ASIMD
>  	b.eq	__fpsimd_guest_restore
>  
> -	mrs	x0, tpidr_el2
> -	mov	x1, #ARM_EXCEPTION_TRAP
> +	ldp     x2, x3, [sp], #16
> +	mrs	x1, tpidr_el2
> +	mov	x0, #ARM_EXCEPTION_TRAP
>  	b	__guest_exit
>  
>  el1_irq:
> -	save_x0_to_x3
> -	mrs	x0, tpidr_el2
> -	mov	x1, #ARM_EXCEPTION_IRQ
> +	stp     x0, x1, [sp, #-16]!
> +	mrs	x1, tpidr_el2
> +	mov	x0, #ARM_EXCEPTION_IRQ
>  	b	__guest_exit
>  
>  ENTRY(__hyp_do_panic)
> -- 
> Qualcomm Datacenter Technologies, Inc. on behalf of the Qualcomm Technologies, Inc.
> Qualcomm Technologies, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project.
> 

^ permalink raw reply	[flat|nested] 10+ messages in thread

* [PATCH v2] arm64: KVM: Save four instructions in __guest_enter/exit()
@ 2016-08-30  9:55   ` Christoffer Dall
  0 siblings, 0 replies; 10+ messages in thread
From: Christoffer Dall @ 2016-08-30  9:55 UTC (permalink / raw)
  To: linux-arm-kernel

On Mon, Aug 29, 2016 at 10:51:14PM -0500, Shanker Donthineni wrote:
> We are doing an unnecessary stack push/pop operation when restoring
> the guest registers x0-x18 in __guest_enter(). This patch saves the
> two instructions by using x18 as a base register. No need to store
> the vcpu context pointer in stack because it is redundant, the same
> information is available in tpidr_el2. The function __guest_exit()
> prototype is simplified and caller pushes the regs x0-x1 to stack
> instead of regs x0-x3.
> 
> Signed-off-by: Shanker Donthineni <shankerd@codeaurora.org>

This looks reasonable to me:

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

Unless Marc has any insight into this having a negative effect on ARM
CPUs, I'll go ahead an merge this.

-Christoffer

> ---
> Changes since v1:
>   Incorporated Cristoffer suggestions.
>   __guest_exit prototype is changed to 'void __guest_exit(u64 reason, struct kvm_vcpu *vcpu)'.
> 
>  arch/arm64/kvm/hyp/entry.S     | 101 +++++++++++++++++++++--------------------
>  arch/arm64/kvm/hyp/hyp-entry.S |  11 +++--
>  2 files changed, 57 insertions(+), 55 deletions(-)
> 
> diff --git a/arch/arm64/kvm/hyp/entry.S b/arch/arm64/kvm/hyp/entry.S
> index ce9e5e5..f70489a 100644
> --- a/arch/arm64/kvm/hyp/entry.S
> +++ b/arch/arm64/kvm/hyp/entry.S
> @@ -55,75 +55,76 @@
>   */
>  ENTRY(__guest_enter)
>  	// x0: vcpu
> -	// x1: host/guest context
> -	// x2-x18: clobbered by macros
> +	// x1: host context
> +	// x2-x17: clobbered by macros
> +	// x18: guest context
>  
>  	// Store the host regs
>  	save_callee_saved_regs x1
>  
> -	// Preserve vcpu & host_ctxt for use at exit time
> -	stp	x0, x1, [sp, #-16]!
> +	// Store the host_ctxt for use at exit time
> +	str	x1, [sp, #-16]!
>  
> -	add	x1, x0, #VCPU_CONTEXT
> +	add	x18, x0, #VCPU_CONTEXT
>  
> -	// Prepare x0-x1 for later restore by pushing them onto the stack
> -	ldp	x2, x3, [x1, #CPU_XREG_OFFSET(0)]
> -	stp	x2, x3, [sp, #-16]!
> +	// Restore guest regs x0-x17
> +	ldp	x0, x1,   [x18, #CPU_XREG_OFFSET(0)]
> +	ldp	x2, x3,   [x18, #CPU_XREG_OFFSET(2)]
> +	ldp	x4, x5,   [x18, #CPU_XREG_OFFSET(4)]
> +	ldp	x6, x7,   [x18, #CPU_XREG_OFFSET(6)]
> +	ldp	x8, x9,   [x18, #CPU_XREG_OFFSET(8)]
> +	ldp	x10, x11, [x18, #CPU_XREG_OFFSET(10)]
> +	ldp	x12, x13, [x18, #CPU_XREG_OFFSET(12)]
> +	ldp	x14, x15, [x18, #CPU_XREG_OFFSET(14)]
> +	ldp	x16, x17, [x18, #CPU_XREG_OFFSET(16)]
>  
> -	// x2-x18
> -	ldp	x2, x3,   [x1, #CPU_XREG_OFFSET(2)]
> -	ldp	x4, x5,   [x1, #CPU_XREG_OFFSET(4)]
> -	ldp	x6, x7,   [x1, #CPU_XREG_OFFSET(6)]
> -	ldp	x8, x9,   [x1, #CPU_XREG_OFFSET(8)]
> -	ldp	x10, x11, [x1, #CPU_XREG_OFFSET(10)]
> -	ldp	x12, x13, [x1, #CPU_XREG_OFFSET(12)]
> -	ldp	x14, x15, [x1, #CPU_XREG_OFFSET(14)]
> -	ldp	x16, x17, [x1, #CPU_XREG_OFFSET(16)]
> -	ldr	x18,      [x1, #CPU_XREG_OFFSET(18)]
> +	// Restore guest regs x19-x29, lr
> +	restore_callee_saved_regs x18
>  
> -	// x19-x29, lr
> -	restore_callee_saved_regs x1
> -
> -	// Last bits of the 64bit state
> -	ldp	x0, x1, [sp], #16
> +	// Restore guest reg x18
> +	ldr	x18,      [x18, #CPU_XREG_OFFSET(18)]
>  
>  	// Do not touch any register after this!
>  	eret
>  ENDPROC(__guest_enter)
>  
> +/*
> + * void __guest_exit(u64 exit_reason, struct kvm_vcpu *vcpu);
> + */
>  ENTRY(__guest_exit)
> -	// x0: vcpu
> -	// x1: return code
> -	// x2-x3: free
> -	// x4-x29,lr: vcpu regs
> -	// vcpu x0-x3 on the stack
> -
> -	add	x2, x0, #VCPU_CONTEXT
> -
> -	stp	x4, x5,   [x2, #CPU_XREG_OFFSET(4)]
> -	stp	x6, x7,   [x2, #CPU_XREG_OFFSET(6)]
> -	stp	x8, x9,   [x2, #CPU_XREG_OFFSET(8)]
> -	stp	x10, x11, [x2, #CPU_XREG_OFFSET(10)]
> -	stp	x12, x13, [x2, #CPU_XREG_OFFSET(12)]
> -	stp	x14, x15, [x2, #CPU_XREG_OFFSET(14)]
> -	stp	x16, x17, [x2, #CPU_XREG_OFFSET(16)]
> -	str	x18,      [x2, #CPU_XREG_OFFSET(18)]
> -
> -	ldp	x6, x7, [sp], #16	// x2, x3
> -	ldp	x4, x5, [sp], #16	// x0, x1
> -
> -	stp	x4, x5, [x2, #CPU_XREG_OFFSET(0)]
> -	stp	x6, x7, [x2, #CPU_XREG_OFFSET(2)]
> +	// x0: return code
> +	// x1: vcpu
> +	// x2-x29,lr: vcpu regs
> +	// vcpu x0-x1 on the stack
> +
> +	add	x1, x1, #VCPU_CONTEXT
> +
> +	// Store the guest regs x2 and x3
> +	stp	x2, x3,   [x1, #CPU_XREG_OFFSET(2)]
> +
> +	// Retrieve the guest regs x0-x1 from the stack
> +	ldp	x2, x3, [sp], #16	// x0, x1
> +
> +	// Store the guest regs x0-x1 and x4-x18
> +	stp	x2, x3,   [x1, #CPU_XREG_OFFSET(0)]
> +	stp	x4, x5,   [x1, #CPU_XREG_OFFSET(4)]
> +	stp	x6, x7,   [x1, #CPU_XREG_OFFSET(6)]
> +	stp	x8, x9,   [x1, #CPU_XREG_OFFSET(8)]
> +	stp	x10, x11, [x1, #CPU_XREG_OFFSET(10)]
> +	stp	x12, x13, [x1, #CPU_XREG_OFFSET(12)]
> +	stp	x14, x15, [x1, #CPU_XREG_OFFSET(14)]
> +	stp	x16, x17, [x1, #CPU_XREG_OFFSET(16)]
> +	str	x18,      [x1, #CPU_XREG_OFFSET(18)]
> +
> +	// Store the guest regs x19-x29, lr
> +	save_callee_saved_regs x1
>  
> -	save_callee_saved_regs x2
> +	// Restore the host_ctxt from the stack
> +	ldr	x2, [sp], #16
>  
> -	// Restore vcpu & host_ctxt from the stack
> -	// (preserving return code in x1)
> -	ldp	x0, x2, [sp], #16
>  	// Now restore the host regs
>  	restore_callee_saved_regs x2
>  
> -	mov	x0, x1
>  	ret
>  ENDPROC(__guest_exit)
>  
> diff --git a/arch/arm64/kvm/hyp/hyp-entry.S b/arch/arm64/kvm/hyp/hyp-entry.S
> index f6d9694..06e8b3b 100644
> --- a/arch/arm64/kvm/hyp/hyp-entry.S
> +++ b/arch/arm64/kvm/hyp/hyp-entry.S
> @@ -121,14 +121,15 @@ el1_trap:
>  	cmp	x2, #ESR_ELx_EC_FP_ASIMD
>  	b.eq	__fpsimd_guest_restore
>  
> -	mrs	x0, tpidr_el2
> -	mov	x1, #ARM_EXCEPTION_TRAP
> +	ldp     x2, x3, [sp], #16
> +	mrs	x1, tpidr_el2
> +	mov	x0, #ARM_EXCEPTION_TRAP
>  	b	__guest_exit
>  
>  el1_irq:
> -	save_x0_to_x3
> -	mrs	x0, tpidr_el2
> -	mov	x1, #ARM_EXCEPTION_IRQ
> +	stp     x0, x1, [sp, #-16]!
> +	mrs	x1, tpidr_el2
> +	mov	x0, #ARM_EXCEPTION_IRQ
>  	b	__guest_exit
>  
>  ENTRY(__hyp_do_panic)
> -- 
> Qualcomm Datacenter Technologies, Inc. on behalf of the Qualcomm Technologies, Inc.
> Qualcomm Technologies, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project.
> 

^ permalink raw reply	[flat|nested] 10+ messages in thread

* Re: [PATCH v2] arm64: KVM: Save four instructions in __guest_enter/exit()
  2016-08-30  9:55   ` Christoffer Dall
@ 2016-08-30 10:54     ` Marc Zyngier
  -1 siblings, 0 replies; 10+ messages in thread
From: Marc Zyngier @ 2016-08-30 10:54 UTC (permalink / raw)
  To: Christoffer Dall, Shanker Donthineni
  Cc: linux-kernel, linux-arm-kernel, kvmarm, Paolo Bonzini,
	Will Deacon, Catalin Marinas, James Morse

On 30/08/16 10:55, Christoffer Dall wrote:
> On Mon, Aug 29, 2016 at 10:51:14PM -0500, Shanker Donthineni wrote:
>> We are doing an unnecessary stack push/pop operation when restoring
>> the guest registers x0-x18 in __guest_enter(). This patch saves the
>> two instructions by using x18 as a base register. No need to store
>> the vcpu context pointer in stack because it is redundant, the same
>> information is available in tpidr_el2. The function __guest_exit()
>> prototype is simplified and caller pushes the regs x0-x1 to stack
>> instead of regs x0-x3.
>>
>> Signed-off-by: Shanker Donthineni <shankerd@codeaurora.org>
> 
> This looks reasonable to me:
> 
> Reviewed-by: Christoffer Dall <christoffer.dall@linaro.org>
> 
> Unless Marc has any insight into this having a negative effect on ARM
> CPUs, I'll go ahead an merge this.

I've given it a go on Seattle, and couldn't observe any difference with
the original code, which is pretty good news!

I have some comments below, though:

> 
> -Christoffer
> 
>> ---
>> Changes since v1:
>>   Incorporated Cristoffer suggestions.
>>   __guest_exit prototype is changed to 'void __guest_exit(u64 reason, struct kvm_vcpu *vcpu)'.
>>
>>  arch/arm64/kvm/hyp/entry.S     | 101 +++++++++++++++++++++--------------------
>>  arch/arm64/kvm/hyp/hyp-entry.S |  11 +++--
>>  2 files changed, 57 insertions(+), 55 deletions(-)
>>
>> diff --git a/arch/arm64/kvm/hyp/entry.S b/arch/arm64/kvm/hyp/entry.S
>> index ce9e5e5..f70489a 100644
>> --- a/arch/arm64/kvm/hyp/entry.S
>> +++ b/arch/arm64/kvm/hyp/entry.S
>> @@ -55,75 +55,76 @@
>>   */
>>  ENTRY(__guest_enter)
>>  	// x0: vcpu
>> -	// x1: host/guest context
>> -	// x2-x18: clobbered by macros
>> +	// x1: host context
>> +	// x2-x17: clobbered by macros
>> +	// x18: guest context
>>  
>>  	// Store the host regs
>>  	save_callee_saved_regs x1
>>  
>> -	// Preserve vcpu & host_ctxt for use at exit time
>> -	stp	x0, x1, [sp, #-16]!
>> +	// Store the host_ctxt for use at exit time
>> +	str	x1, [sp, #-16]!
>>  
>> -	add	x1, x0, #VCPU_CONTEXT
>> +	add	x18, x0, #VCPU_CONTEXT
>>  
>> -	// Prepare x0-x1 for later restore by pushing them onto the stack
>> -	ldp	x2, x3, [x1, #CPU_XREG_OFFSET(0)]
>> -	stp	x2, x3, [sp, #-16]!
>> +	// Restore guest regs x0-x17
>> +	ldp	x0, x1,   [x18, #CPU_XREG_OFFSET(0)]
>> +	ldp	x2, x3,   [x18, #CPU_XREG_OFFSET(2)]
>> +	ldp	x4, x5,   [x18, #CPU_XREG_OFFSET(4)]
>> +	ldp	x6, x7,   [x18, #CPU_XREG_OFFSET(6)]
>> +	ldp	x8, x9,   [x18, #CPU_XREG_OFFSET(8)]
>> +	ldp	x10, x11, [x18, #CPU_XREG_OFFSET(10)]
>> +	ldp	x12, x13, [x18, #CPU_XREG_OFFSET(12)]
>> +	ldp	x14, x15, [x18, #CPU_XREG_OFFSET(14)]
>> +	ldp	x16, x17, [x18, #CPU_XREG_OFFSET(16)]
>>  
>> -	// x2-x18
>> -	ldp	x2, x3,   [x1, #CPU_XREG_OFFSET(2)]
>> -	ldp	x4, x5,   [x1, #CPU_XREG_OFFSET(4)]
>> -	ldp	x6, x7,   [x1, #CPU_XREG_OFFSET(6)]
>> -	ldp	x8, x9,   [x1, #CPU_XREG_OFFSET(8)]
>> -	ldp	x10, x11, [x1, #CPU_XREG_OFFSET(10)]
>> -	ldp	x12, x13, [x1, #CPU_XREG_OFFSET(12)]
>> -	ldp	x14, x15, [x1, #CPU_XREG_OFFSET(14)]
>> -	ldp	x16, x17, [x1, #CPU_XREG_OFFSET(16)]
>> -	ldr	x18,      [x1, #CPU_XREG_OFFSET(18)]
>> +	// Restore guest regs x19-x29, lr
>> +	restore_callee_saved_regs x18
>>  
>> -	// x19-x29, lr
>> -	restore_callee_saved_regs x1
>> -
>> -	// Last bits of the 64bit state
>> -	ldp	x0, x1, [sp], #16
>> +	// Restore guest reg x18
>> +	ldr	x18,      [x18, #CPU_XREG_OFFSET(18)]
>>  
>>  	// Do not touch any register after this!
>>  	eret
>>  ENDPROC(__guest_enter)
>>  
>> +/*
>> + * void __guest_exit(u64 exit_reason, struct kvm_vcpu *vcpu);
>> + */

I'm not sure this comment makes much sense as it stands. This is not a C
function by any stretch of the imagination, but the continuation of
__guest_enter. The calling convention is not the C one at all (see how
the stack is involved), and caller-saved registers are going to be
clobbered.

>>  ENTRY(__guest_exit)
>> -	// x0: vcpu
>> -	// x1: return code
>> -	// x2-x3: free
>> -	// x4-x29,lr: vcpu regs
>> -	// vcpu x0-x3 on the stack
>> -
>> -	add	x2, x0, #VCPU_CONTEXT
>> -
>> -	stp	x4, x5,   [x2, #CPU_XREG_OFFSET(4)]
>> -	stp	x6, x7,   [x2, #CPU_XREG_OFFSET(6)]
>> -	stp	x8, x9,   [x2, #CPU_XREG_OFFSET(8)]
>> -	stp	x10, x11, [x2, #CPU_XREG_OFFSET(10)]
>> -	stp	x12, x13, [x2, #CPU_XREG_OFFSET(12)]
>> -	stp	x14, x15, [x2, #CPU_XREG_OFFSET(14)]
>> -	stp	x16, x17, [x2, #CPU_XREG_OFFSET(16)]
>> -	str	x18,      [x2, #CPU_XREG_OFFSET(18)]
>> -
>> -	ldp	x6, x7, [sp], #16	// x2, x3
>> -	ldp	x4, x5, [sp], #16	// x0, x1
>> -
>> -	stp	x4, x5, [x2, #CPU_XREG_OFFSET(0)]
>> -	stp	x6, x7, [x2, #CPU_XREG_OFFSET(2)]
>> +	// x0: return code
>> +	// x1: vcpu
>> +	// x2-x29,lr: vcpu regs
>> +	// vcpu x0-x1 on the stack
>> +
>> +	add	x1, x1, #VCPU_CONTEXT
>> +
>> +	// Store the guest regs x2 and x3
>> +	stp	x2, x3,   [x1, #CPU_XREG_OFFSET(2)]
>> +
>> +	// Retrieve the guest regs x0-x1 from the stack
>> +	ldp	x2, x3, [sp], #16	// x0, x1
>> +
>> +	// Store the guest regs x0-x1 and x4-x18
>> +	stp	x2, x3,   [x1, #CPU_XREG_OFFSET(0)]
>> +	stp	x4, x5,   [x1, #CPU_XREG_OFFSET(4)]
>> +	stp	x6, x7,   [x1, #CPU_XREG_OFFSET(6)]
>> +	stp	x8, x9,   [x1, #CPU_XREG_OFFSET(8)]
>> +	stp	x10, x11, [x1, #CPU_XREG_OFFSET(10)]
>> +	stp	x12, x13, [x1, #CPU_XREG_OFFSET(12)]
>> +	stp	x14, x15, [x1, #CPU_XREG_OFFSET(14)]
>> +	stp	x16, x17, [x1, #CPU_XREG_OFFSET(16)]
>> +	str	x18,      [x1, #CPU_XREG_OFFSET(18)]
>> +
>> +	// Store the guest regs x19-x29, lr
>> +	save_callee_saved_regs x1
>>  
>> -	save_callee_saved_regs x2
>> +	// Restore the host_ctxt from the stack
>> +	ldr	x2, [sp], #16
>>  
>> -	// Restore vcpu & host_ctxt from the stack
>> -	// (preserving return code in x1)
>> -	ldp	x0, x2, [sp], #16
>>  	// Now restore the host regs
>>  	restore_callee_saved_regs x2
>>  
>> -	mov	x0, x1
>>  	ret
>>  ENDPROC(__guest_exit)
>>  
>> diff --git a/arch/arm64/kvm/hyp/hyp-entry.S b/arch/arm64/kvm/hyp/hyp-entry.S
>> index f6d9694..06e8b3b 100644
>> --- a/arch/arm64/kvm/hyp/hyp-entry.S
>> +++ b/arch/arm64/kvm/hyp/hyp-entry.S
>> @@ -121,14 +121,15 @@ el1_trap:
>>  	cmp	x2, #ESR_ELx_EC_FP_ASIMD
>>  	b.eq	__fpsimd_guest_restore
>>  
>> -	mrs	x0, tpidr_el2
>> -	mov	x1, #ARM_EXCEPTION_TRAP
>> +	ldp     x2, x3, [sp], #16
>> +	mrs	x1, tpidr_el2
>> +	mov	x0, #ARM_EXCEPTION_TRAP
>>  	b	__guest_exit
>>  
>>  el1_irq:
>> -	save_x0_to_x3

So the save_x0_to_x3 macro now only has one single user (and so does
restore_x0_to_x3).  Should we consider inline it?

>> -	mrs	x0, tpidr_el2
>> -	mov	x1, #ARM_EXCEPTION_IRQ
>> +	stp     x0, x1, [sp, #-16]!
>> +	mrs	x1, tpidr_el2
>> +	mov	x0, #ARM_EXCEPTION_IRQ
>>  	b	__guest_exit
>>  
>>  ENTRY(__hyp_do_panic)
>> -- 
>> Qualcomm Datacenter Technologies, Inc. on behalf of the Qualcomm Technologies, Inc.
>> Qualcomm Technologies, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project.
>>
> 

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...

^ permalink raw reply	[flat|nested] 10+ messages in thread

* [PATCH v2] arm64: KVM: Save four instructions in __guest_enter/exit()
@ 2016-08-30 10:54     ` Marc Zyngier
  0 siblings, 0 replies; 10+ messages in thread
From: Marc Zyngier @ 2016-08-30 10:54 UTC (permalink / raw)
  To: linux-arm-kernel

On 30/08/16 10:55, Christoffer Dall wrote:
> On Mon, Aug 29, 2016 at 10:51:14PM -0500, Shanker Donthineni wrote:
>> We are doing an unnecessary stack push/pop operation when restoring
>> the guest registers x0-x18 in __guest_enter(). This patch saves the
>> two instructions by using x18 as a base register. No need to store
>> the vcpu context pointer in stack because it is redundant, the same
>> information is available in tpidr_el2. The function __guest_exit()
>> prototype is simplified and caller pushes the regs x0-x1 to stack
>> instead of regs x0-x3.
>>
>> Signed-off-by: Shanker Donthineni <shankerd@codeaurora.org>
> 
> This looks reasonable to me:
> 
> Reviewed-by: Christoffer Dall <christoffer.dall@linaro.org>
> 
> Unless Marc has any insight into this having a negative effect on ARM
> CPUs, I'll go ahead an merge this.

I've given it a go on Seattle, and couldn't observe any difference with
the original code, which is pretty good news!

I have some comments below, though:

> 
> -Christoffer
> 
>> ---
>> Changes since v1:
>>   Incorporated Cristoffer suggestions.
>>   __guest_exit prototype is changed to 'void __guest_exit(u64 reason, struct kvm_vcpu *vcpu)'.
>>
>>  arch/arm64/kvm/hyp/entry.S     | 101 +++++++++++++++++++++--------------------
>>  arch/arm64/kvm/hyp/hyp-entry.S |  11 +++--
>>  2 files changed, 57 insertions(+), 55 deletions(-)
>>
>> diff --git a/arch/arm64/kvm/hyp/entry.S b/arch/arm64/kvm/hyp/entry.S
>> index ce9e5e5..f70489a 100644
>> --- a/arch/arm64/kvm/hyp/entry.S
>> +++ b/arch/arm64/kvm/hyp/entry.S
>> @@ -55,75 +55,76 @@
>>   */
>>  ENTRY(__guest_enter)
>>  	// x0: vcpu
>> -	// x1: host/guest context
>> -	// x2-x18: clobbered by macros
>> +	// x1: host context
>> +	// x2-x17: clobbered by macros
>> +	// x18: guest context
>>  
>>  	// Store the host regs
>>  	save_callee_saved_regs x1
>>  
>> -	// Preserve vcpu & host_ctxt for use at exit time
>> -	stp	x0, x1, [sp, #-16]!
>> +	// Store the host_ctxt for use at exit time
>> +	str	x1, [sp, #-16]!
>>  
>> -	add	x1, x0, #VCPU_CONTEXT
>> +	add	x18, x0, #VCPU_CONTEXT
>>  
>> -	// Prepare x0-x1 for later restore by pushing them onto the stack
>> -	ldp	x2, x3, [x1, #CPU_XREG_OFFSET(0)]
>> -	stp	x2, x3, [sp, #-16]!
>> +	// Restore guest regs x0-x17
>> +	ldp	x0, x1,   [x18, #CPU_XREG_OFFSET(0)]
>> +	ldp	x2, x3,   [x18, #CPU_XREG_OFFSET(2)]
>> +	ldp	x4, x5,   [x18, #CPU_XREG_OFFSET(4)]
>> +	ldp	x6, x7,   [x18, #CPU_XREG_OFFSET(6)]
>> +	ldp	x8, x9,   [x18, #CPU_XREG_OFFSET(8)]
>> +	ldp	x10, x11, [x18, #CPU_XREG_OFFSET(10)]
>> +	ldp	x12, x13, [x18, #CPU_XREG_OFFSET(12)]
>> +	ldp	x14, x15, [x18, #CPU_XREG_OFFSET(14)]
>> +	ldp	x16, x17, [x18, #CPU_XREG_OFFSET(16)]
>>  
>> -	// x2-x18
>> -	ldp	x2, x3,   [x1, #CPU_XREG_OFFSET(2)]
>> -	ldp	x4, x5,   [x1, #CPU_XREG_OFFSET(4)]
>> -	ldp	x6, x7,   [x1, #CPU_XREG_OFFSET(6)]
>> -	ldp	x8, x9,   [x1, #CPU_XREG_OFFSET(8)]
>> -	ldp	x10, x11, [x1, #CPU_XREG_OFFSET(10)]
>> -	ldp	x12, x13, [x1, #CPU_XREG_OFFSET(12)]
>> -	ldp	x14, x15, [x1, #CPU_XREG_OFFSET(14)]
>> -	ldp	x16, x17, [x1, #CPU_XREG_OFFSET(16)]
>> -	ldr	x18,      [x1, #CPU_XREG_OFFSET(18)]
>> +	// Restore guest regs x19-x29, lr
>> +	restore_callee_saved_regs x18
>>  
>> -	// x19-x29, lr
>> -	restore_callee_saved_regs x1
>> -
>> -	// Last bits of the 64bit state
>> -	ldp	x0, x1, [sp], #16
>> +	// Restore guest reg x18
>> +	ldr	x18,      [x18, #CPU_XREG_OFFSET(18)]
>>  
>>  	// Do not touch any register after this!
>>  	eret
>>  ENDPROC(__guest_enter)
>>  
>> +/*
>> + * void __guest_exit(u64 exit_reason, struct kvm_vcpu *vcpu);
>> + */

I'm not sure this comment makes much sense as it stands. This is not a C
function by any stretch of the imagination, but the continuation of
__guest_enter. The calling convention is not the C one at all (see how
the stack is involved), and caller-saved registers are going to be
clobbered.

>>  ENTRY(__guest_exit)
>> -	// x0: vcpu
>> -	// x1: return code
>> -	// x2-x3: free
>> -	// x4-x29,lr: vcpu regs
>> -	// vcpu x0-x3 on the stack
>> -
>> -	add	x2, x0, #VCPU_CONTEXT
>> -
>> -	stp	x4, x5,   [x2, #CPU_XREG_OFFSET(4)]
>> -	stp	x6, x7,   [x2, #CPU_XREG_OFFSET(6)]
>> -	stp	x8, x9,   [x2, #CPU_XREG_OFFSET(8)]
>> -	stp	x10, x11, [x2, #CPU_XREG_OFFSET(10)]
>> -	stp	x12, x13, [x2, #CPU_XREG_OFFSET(12)]
>> -	stp	x14, x15, [x2, #CPU_XREG_OFFSET(14)]
>> -	stp	x16, x17, [x2, #CPU_XREG_OFFSET(16)]
>> -	str	x18,      [x2, #CPU_XREG_OFFSET(18)]
>> -
>> -	ldp	x6, x7, [sp], #16	// x2, x3
>> -	ldp	x4, x5, [sp], #16	// x0, x1
>> -
>> -	stp	x4, x5, [x2, #CPU_XREG_OFFSET(0)]
>> -	stp	x6, x7, [x2, #CPU_XREG_OFFSET(2)]
>> +	// x0: return code
>> +	// x1: vcpu
>> +	// x2-x29,lr: vcpu regs
>> +	// vcpu x0-x1 on the stack
>> +
>> +	add	x1, x1, #VCPU_CONTEXT
>> +
>> +	// Store the guest regs x2 and x3
>> +	stp	x2, x3,   [x1, #CPU_XREG_OFFSET(2)]
>> +
>> +	// Retrieve the guest regs x0-x1 from the stack
>> +	ldp	x2, x3, [sp], #16	// x0, x1
>> +
>> +	// Store the guest regs x0-x1 and x4-x18
>> +	stp	x2, x3,   [x1, #CPU_XREG_OFFSET(0)]
>> +	stp	x4, x5,   [x1, #CPU_XREG_OFFSET(4)]
>> +	stp	x6, x7,   [x1, #CPU_XREG_OFFSET(6)]
>> +	stp	x8, x9,   [x1, #CPU_XREG_OFFSET(8)]
>> +	stp	x10, x11, [x1, #CPU_XREG_OFFSET(10)]
>> +	stp	x12, x13, [x1, #CPU_XREG_OFFSET(12)]
>> +	stp	x14, x15, [x1, #CPU_XREG_OFFSET(14)]
>> +	stp	x16, x17, [x1, #CPU_XREG_OFFSET(16)]
>> +	str	x18,      [x1, #CPU_XREG_OFFSET(18)]
>> +
>> +	// Store the guest regs x19-x29, lr
>> +	save_callee_saved_regs x1
>>  
>> -	save_callee_saved_regs x2
>> +	// Restore the host_ctxt from the stack
>> +	ldr	x2, [sp], #16
>>  
>> -	// Restore vcpu & host_ctxt from the stack
>> -	// (preserving return code in x1)
>> -	ldp	x0, x2, [sp], #16
>>  	// Now restore the host regs
>>  	restore_callee_saved_regs x2
>>  
>> -	mov	x0, x1
>>  	ret
>>  ENDPROC(__guest_exit)
>>  
>> diff --git a/arch/arm64/kvm/hyp/hyp-entry.S b/arch/arm64/kvm/hyp/hyp-entry.S
>> index f6d9694..06e8b3b 100644
>> --- a/arch/arm64/kvm/hyp/hyp-entry.S
>> +++ b/arch/arm64/kvm/hyp/hyp-entry.S
>> @@ -121,14 +121,15 @@ el1_trap:
>>  	cmp	x2, #ESR_ELx_EC_FP_ASIMD
>>  	b.eq	__fpsimd_guest_restore
>>  
>> -	mrs	x0, tpidr_el2
>> -	mov	x1, #ARM_EXCEPTION_TRAP
>> +	ldp     x2, x3, [sp], #16
>> +	mrs	x1, tpidr_el2
>> +	mov	x0, #ARM_EXCEPTION_TRAP
>>  	b	__guest_exit
>>  
>>  el1_irq:
>> -	save_x0_to_x3

So the save_x0_to_x3 macro now only has one single user (and so does
restore_x0_to_x3).  Should we consider inline it?

>> -	mrs	x0, tpidr_el2
>> -	mov	x1, #ARM_EXCEPTION_IRQ
>> +	stp     x0, x1, [sp, #-16]!
>> +	mrs	x1, tpidr_el2
>> +	mov	x0, #ARM_EXCEPTION_IRQ
>>  	b	__guest_exit
>>  
>>  ENTRY(__hyp_do_panic)
>> -- 
>> Qualcomm Datacenter Technologies, Inc. on behalf of the Qualcomm Technologies, Inc.
>> Qualcomm Technologies, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project.
>>
> 

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...

^ permalink raw reply	[flat|nested] 10+ messages in thread

* Re: [PATCH v2] arm64: KVM: Save four instructions in __guest_enter/exit()
  2016-08-30 10:54     ` Marc Zyngier
  (?)
@ 2016-08-30 12:22       ` Shanker Donthineni
  -1 siblings, 0 replies; 10+ messages in thread
From: Shanker Donthineni @ 2016-08-30 12:22 UTC (permalink / raw)
  To: Marc Zyngier, Christoffer Dall
  Cc: linux-kernel, linux-arm-kernel, kvmarm, Paolo Bonzini,
	Will Deacon, Catalin Marinas, James Morse

Hi Marc,


On 08/30/2016 05:54 AM, Marc Zyngier wrote:
> On 30/08/16 10:55, Christoffer Dall wrote:
>> On Mon, Aug 29, 2016 at 10:51:14PM -0500, Shanker Donthineni wrote:
>>> We are doing an unnecessary stack push/pop operation when restoring
>>> the guest registers x0-x18 in __guest_enter(). This patch saves the
>>> two instructions by using x18 as a base register. No need to store
>>> the vcpu context pointer in stack because it is redundant, the same
>>> information is available in tpidr_el2. The function __guest_exit()
>>> prototype is simplified and caller pushes the regs x0-x1 to stack
>>> instead of regs x0-x3.
>>>
>>> Signed-off-by: Shanker Donthineni <shankerd@codeaurora.org>
>> This looks reasonable to me:
>>
>> Reviewed-by: Christoffer Dall <christoffer.dall@linaro.org>
>>
>> Unless Marc has any insight into this having a negative effect on ARM
>> CPUs, I'll go ahead an merge this.
> I've given it a go on Seattle, and couldn't observe any difference with
> the original code, which is pretty good news!
>
> I have some comments below, though:
>
>> -Christoffer
>>
>>> ---
>>> Changes since v1:
>>>    Incorporated Cristoffer suggestions.
>>>    __guest_exit prototype is changed to 'void __guest_exit(u64 reason,
> struct kvm_vcpu *vcpu)'.
>>>   arch/arm64/kvm/hyp/entry.S     | 101
> +++++++++++++++++++++--------------------
>>>   arch/arm64/kvm/hyp/hyp-entry.S |  11 +++--
>>>   2 files changed, 57 insertions(+), 55 deletions(-)
>>>
>>> diff --git a/arch/arm64/kvm/hyp/entry.S b/arch/arm64/kvm/hyp/entry.S
>>> index ce9e5e5..f70489a 100644
>>> --- a/arch/arm64/kvm/hyp/entry.S
>>> +++ b/arch/arm64/kvm/hyp/entry.S
>>> @@ -55,75 +55,76 @@
>>>    */
>>>   ENTRY(__guest_enter)
>>>   	// x0: vcpu
>>> -	// x1: host/guest context
>>> -	// x2-x18: clobbered by macros
>>> +	// x1: host context
>>> +	// x2-x17: clobbered by macros
>>> +	// x18: guest context
>>>   
>>>   	// Store the host regs
>>>   	save_callee_saved_regs x1
>>>   
>>> -	// Preserve vcpu & host_ctxt for use at exit time
>>> -	stp	x0, x1, [sp, #-16]!
>>> +	// Store the host_ctxt for use at exit time
>>> +	str	x1, [sp, #-16]!
>>>   
>>> -	add	x1, x0, #VCPU_CONTEXT
>>> +	add	x18, x0, #VCPU_CONTEXT
>>>   
>>> -	// Prepare x0-x1 for later restore by pushing them onto the stack
>>> -	ldp	x2, x3, [x1, #CPU_XREG_OFFSET(0)]
>>> -	stp	x2, x3, [sp, #-16]!
>>> +	// Restore guest regs x0-x17
>>> +	ldp	x0, x1,   [x18, #CPU_XREG_OFFSET(0)]
>>> +	ldp	x2, x3,   [x18, #CPU_XREG_OFFSET(2)]
>>> +	ldp	x4, x5,   [x18, #CPU_XREG_OFFSET(4)]
>>> +	ldp	x6, x7,   [x18, #CPU_XREG_OFFSET(6)]
>>> +	ldp	x8, x9,   [x18, #CPU_XREG_OFFSET(8)]
>>> +	ldp	x10, x11, [x18, #CPU_XREG_OFFSET(10)]
>>> +	ldp	x12, x13, [x18, #CPU_XREG_OFFSET(12)]
>>> +	ldp	x14, x15, [x18, #CPU_XREG_OFFSET(14)]
>>> +	ldp	x16, x17, [x18, #CPU_XREG_OFFSET(16)]
>>>   
>>> -	// x2-x18
>>> -	ldp	x2, x3,   [x1, #CPU_XREG_OFFSET(2)]
>>> -	ldp	x4, x5,   [x1, #CPU_XREG_OFFSET(4)]
>>> -	ldp	x6, x7,   [x1, #CPU_XREG_OFFSET(6)]
>>> -	ldp	x8, x9,   [x1, #CPU_XREG_OFFSET(8)]
>>> -	ldp	x10, x11, [x1, #CPU_XREG_OFFSET(10)]
>>> -	ldp	x12, x13, [x1, #CPU_XREG_OFFSET(12)]
>>> -	ldp	x14, x15, [x1, #CPU_XREG_OFFSET(14)]
>>> -	ldp	x16, x17, [x1, #CPU_XREG_OFFSET(16)]
>>> -	ldr	x18,      [x1, #CPU_XREG_OFFSET(18)]
>>> +	// Restore guest regs x19-x29, lr
>>> +	restore_callee_saved_regs x18
>>>   
>>> -	// x19-x29, lr
>>> -	restore_callee_saved_regs x1
>>> -
>>> -	// Last bits of the 64bit state
>>> -	ldp	x0, x1, [sp], #16
>>> +	// Restore guest reg x18
>>> +	ldr	x18,      [x18, #CPU_XREG_OFFSET(18)]
>>>   
>>>   	// Do not touch any register after this!
>>>   	eret
>>>   ENDPROC(__guest_enter)
>>>   
>>> +/*
>>> + * void __guest_exit(u64 exit_reason, struct kvm_vcpu *vcpu);
>>> + */
> I'm not sure this comment makes much sense as it stands. This is not a C
> function by any stretch of the imagination, but the continuation of
> __guest_enter. The calling convention is not the C one at all (see how
> the stack is involved), and caller-saved registers are going to be
> clobbered.

I'll remove this confusing comments.

>>>   ENTRY(__guest_exit)
>>> -	// x0: vcpu
>>> -	// x1: return code
>>> -	// x2-x3: free
>>> -	// x4-x29,lr: vcpu regs
>>> -	// vcpu x0-x3 on the stack
>>> -
>>> -	add	x2, x0, #VCPU_CONTEXT
>>> -
>>> -	stp	x4, x5,   [x2, #CPU_XREG_OFFSET(4)]
>>> -	stp	x6, x7,   [x2, #CPU_XREG_OFFSET(6)]
>>> -	stp	x8, x9,   [x2, #CPU_XREG_OFFSET(8)]
>>> -	stp	x10, x11, [x2, #CPU_XREG_OFFSET(10)]
>>> -	stp	x12, x13, [x2, #CPU_XREG_OFFSET(12)]
>>> -	stp	x14, x15, [x2, #CPU_XREG_OFFSET(14)]
>>> -	stp	x16, x17, [x2, #CPU_XREG_OFFSET(16)]
>>> -	str	x18,      [x2, #CPU_XREG_OFFSET(18)]
>>> -
>>> -	ldp	x6, x7, [sp], #16	// x2, x3
>>> -	ldp	x4, x5, [sp], #16	// x0, x1
>>> -
>>> -	stp	x4, x5, [x2, #CPU_XREG_OFFSET(0)]
>>> -	stp	x6, x7, [x2, #CPU_XREG_OFFSET(2)]
>>> +	// x0: return code
>>> +	// x1: vcpu
>>> +	// x2-x29,lr: vcpu regs
>>> +	// vcpu x0-x1 on the stack
>>> +
>>> +	add	x1, x1, #VCPU_CONTEXT
>>> +
>>> +	// Store the guest regs x2 and x3
>>> +	stp	x2, x3,   [x1, #CPU_XREG_OFFSET(2)]
>>> +
>>> +	// Retrieve the guest regs x0-x1 from the stack
>>> +	ldp	x2, x3, [sp], #16	// x0, x1
>>> +
>>> +	// Store the guest regs x0-x1 and x4-x18
>>> +	stp	x2, x3,   [x1, #CPU_XREG_OFFSET(0)]
>>> +	stp	x4, x5,   [x1, #CPU_XREG_OFFSET(4)]
>>> +	stp	x6, x7,   [x1, #CPU_XREG_OFFSET(6)]
>>> +	stp	x8, x9,   [x1, #CPU_XREG_OFFSET(8)]
>>> +	stp	x10, x11, [x1, #CPU_XREG_OFFSET(10)]
>>> +	stp	x12, x13, [x1, #CPU_XREG_OFFSET(12)]
>>> +	stp	x14, x15, [x1, #CPU_XREG_OFFSET(14)]
>>> +	stp	x16, x17, [x1, #CPU_XREG_OFFSET(16)]
>>> +	str	x18,      [x1, #CPU_XREG_OFFSET(18)]
>>> +
>>> +	// Store the guest regs x19-x29, lr
>>> +	save_callee_saved_regs x1
>>>   
>>> -	save_callee_saved_regs x2
>>> +	// Restore the host_ctxt from the stack
>>> +	ldr	x2, [sp], #16
>>>   
>>> -	// Restore vcpu & host_ctxt from the stack
>>> -	// (preserving return code in x1)
>>> -	ldp	x0, x2, [sp], #16
>>>   	// Now restore the host regs
>>>   	restore_callee_saved_regs x2
>>>   
>>> -	mov	x0, x1
>>>   	ret
>>>   ENDPROC(__guest_exit)
>>>   
>>> diff --git a/arch/arm64/kvm/hyp/hyp-entry.S
> b/arch/arm64/kvm/hyp/hyp-entry.S
>>> index f6d9694..06e8b3b 100644
>>> --- a/arch/arm64/kvm/hyp/hyp-entry.S
>>> +++ b/arch/arm64/kvm/hyp/hyp-entry.S
>>> @@ -121,14 +121,15 @@ el1_trap:
>>>   	cmp	x2, #ESR_ELx_EC_FP_ASIMD
>>>   	b.eq	__fpsimd_guest_restore
>>>   
>>> -	mrs	x0, tpidr_el2
>>> -	mov	x1, #ARM_EXCEPTION_TRAP
>>> +	ldp     x2, x3, [sp], #16
>>> +	mrs	x1, tpidr_el2
>>> +	mov	x0, #ARM_EXCEPTION_TRAP
>>>   	b	__guest_exit
>>>   
>>>   el1_irq:
>>> -	save_x0_to_x3
> So the save_x0_to_x3 macro now only has one single user (and so does
> restore_x0_to_x3).  Should we consider inline it?

Sure, I'll change to inline in v3 patch.

>>> -	mrs	x0, tpidr_el2
>>> -	mov	x1, #ARM_EXCEPTION_IRQ
>>> +	stp     x0, x1, [sp, #-16]!
>>> +	mrs	x1, tpidr_el2
>>> +	mov	x0, #ARM_EXCEPTION_IRQ
>>>   	b	__guest_exit
>>>   
>>>   ENTRY(__hyp_do_panic)
>>> -- 
>>> Qualcomm Datacenter Technologies, Inc. on behalf of the Qualcomm
> Technologies, Inc.
>>> Qualcomm Technologies, Inc. is a member of the Code Aurora Forum, a
> Linux Foundation Collaborative Project.
> Thanks,
>
> 	M.

-- 
Shanker Donthineni
Qualcomm Datacenter Technologies, Inc. as an affiliate of Qualcomm Technologies, Inc.
Qualcomm Technologies, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project.

^ permalink raw reply	[flat|nested] 10+ messages in thread

* Re: [PATCH v2] arm64: KVM: Save four instructions in __guest_enter/exit()
@ 2016-08-30 12:22       ` Shanker Donthineni
  0 siblings, 0 replies; 10+ messages in thread
From: Shanker Donthineni @ 2016-08-30 12:22 UTC (permalink / raw)
  To: Marc Zyngier, Christoffer Dall
  Cc: Catalin Marinas, Will Deacon, linux-kernel, Paolo Bonzini,
	kvmarm, linux-arm-kernel

Hi Marc,


On 08/30/2016 05:54 AM, Marc Zyngier wrote:
> On 30/08/16 10:55, Christoffer Dall wrote:
>> On Mon, Aug 29, 2016 at 10:51:14PM -0500, Shanker Donthineni wrote:
>>> We are doing an unnecessary stack push/pop operation when restoring
>>> the guest registers x0-x18 in __guest_enter(). This patch saves the
>>> two instructions by using x18 as a base register. No need to store
>>> the vcpu context pointer in stack because it is redundant, the same
>>> information is available in tpidr_el2. The function __guest_exit()
>>> prototype is simplified and caller pushes the regs x0-x1 to stack
>>> instead of regs x0-x3.
>>>
>>> Signed-off-by: Shanker Donthineni <shankerd@codeaurora.org>
>> This looks reasonable to me:
>>
>> Reviewed-by: Christoffer Dall <christoffer.dall@linaro.org>
>>
>> Unless Marc has any insight into this having a negative effect on ARM
>> CPUs, I'll go ahead an merge this.
> I've given it a go on Seattle, and couldn't observe any difference with
> the original code, which is pretty good news!
>
> I have some comments below, though:
>
>> -Christoffer
>>
>>> ---
>>> Changes since v1:
>>>    Incorporated Cristoffer suggestions.
>>>    __guest_exit prototype is changed to 'void __guest_exit(u64 reason,
> struct kvm_vcpu *vcpu)'.
>>>   arch/arm64/kvm/hyp/entry.S     | 101
> +++++++++++++++++++++--------------------
>>>   arch/arm64/kvm/hyp/hyp-entry.S |  11 +++--
>>>   2 files changed, 57 insertions(+), 55 deletions(-)
>>>
>>> diff --git a/arch/arm64/kvm/hyp/entry.S b/arch/arm64/kvm/hyp/entry.S
>>> index ce9e5e5..f70489a 100644
>>> --- a/arch/arm64/kvm/hyp/entry.S
>>> +++ b/arch/arm64/kvm/hyp/entry.S
>>> @@ -55,75 +55,76 @@
>>>    */
>>>   ENTRY(__guest_enter)
>>>   	// x0: vcpu
>>> -	// x1: host/guest context
>>> -	// x2-x18: clobbered by macros
>>> +	// x1: host context
>>> +	// x2-x17: clobbered by macros
>>> +	// x18: guest context
>>>   
>>>   	// Store the host regs
>>>   	save_callee_saved_regs x1
>>>   
>>> -	// Preserve vcpu & host_ctxt for use at exit time
>>> -	stp	x0, x1, [sp, #-16]!
>>> +	// Store the host_ctxt for use at exit time
>>> +	str	x1, [sp, #-16]!
>>>   
>>> -	add	x1, x0, #VCPU_CONTEXT
>>> +	add	x18, x0, #VCPU_CONTEXT
>>>   
>>> -	// Prepare x0-x1 for later restore by pushing them onto the stack
>>> -	ldp	x2, x3, [x1, #CPU_XREG_OFFSET(0)]
>>> -	stp	x2, x3, [sp, #-16]!
>>> +	// Restore guest regs x0-x17
>>> +	ldp	x0, x1,   [x18, #CPU_XREG_OFFSET(0)]
>>> +	ldp	x2, x3,   [x18, #CPU_XREG_OFFSET(2)]
>>> +	ldp	x4, x5,   [x18, #CPU_XREG_OFFSET(4)]
>>> +	ldp	x6, x7,   [x18, #CPU_XREG_OFFSET(6)]
>>> +	ldp	x8, x9,   [x18, #CPU_XREG_OFFSET(8)]
>>> +	ldp	x10, x11, [x18, #CPU_XREG_OFFSET(10)]
>>> +	ldp	x12, x13, [x18, #CPU_XREG_OFFSET(12)]
>>> +	ldp	x14, x15, [x18, #CPU_XREG_OFFSET(14)]
>>> +	ldp	x16, x17, [x18, #CPU_XREG_OFFSET(16)]
>>>   
>>> -	// x2-x18
>>> -	ldp	x2, x3,   [x1, #CPU_XREG_OFFSET(2)]
>>> -	ldp	x4, x5,   [x1, #CPU_XREG_OFFSET(4)]
>>> -	ldp	x6, x7,   [x1, #CPU_XREG_OFFSET(6)]
>>> -	ldp	x8, x9,   [x1, #CPU_XREG_OFFSET(8)]
>>> -	ldp	x10, x11, [x1, #CPU_XREG_OFFSET(10)]
>>> -	ldp	x12, x13, [x1, #CPU_XREG_OFFSET(12)]
>>> -	ldp	x14, x15, [x1, #CPU_XREG_OFFSET(14)]
>>> -	ldp	x16, x17, [x1, #CPU_XREG_OFFSET(16)]
>>> -	ldr	x18,      [x1, #CPU_XREG_OFFSET(18)]
>>> +	// Restore guest regs x19-x29, lr
>>> +	restore_callee_saved_regs x18
>>>   
>>> -	// x19-x29, lr
>>> -	restore_callee_saved_regs x1
>>> -
>>> -	// Last bits of the 64bit state
>>> -	ldp	x0, x1, [sp], #16
>>> +	// Restore guest reg x18
>>> +	ldr	x18,      [x18, #CPU_XREG_OFFSET(18)]
>>>   
>>>   	// Do not touch any register after this!
>>>   	eret
>>>   ENDPROC(__guest_enter)
>>>   
>>> +/*
>>> + * void __guest_exit(u64 exit_reason, struct kvm_vcpu *vcpu);
>>> + */
> I'm not sure this comment makes much sense as it stands. This is not a C
> function by any stretch of the imagination, but the continuation of
> __guest_enter. The calling convention is not the C one at all (see how
> the stack is involved), and caller-saved registers are going to be
> clobbered.

I'll remove this confusing comments.

>>>   ENTRY(__guest_exit)
>>> -	// x0: vcpu
>>> -	// x1: return code
>>> -	// x2-x3: free
>>> -	// x4-x29,lr: vcpu regs
>>> -	// vcpu x0-x3 on the stack
>>> -
>>> -	add	x2, x0, #VCPU_CONTEXT
>>> -
>>> -	stp	x4, x5,   [x2, #CPU_XREG_OFFSET(4)]
>>> -	stp	x6, x7,   [x2, #CPU_XREG_OFFSET(6)]
>>> -	stp	x8, x9,   [x2, #CPU_XREG_OFFSET(8)]
>>> -	stp	x10, x11, [x2, #CPU_XREG_OFFSET(10)]
>>> -	stp	x12, x13, [x2, #CPU_XREG_OFFSET(12)]
>>> -	stp	x14, x15, [x2, #CPU_XREG_OFFSET(14)]
>>> -	stp	x16, x17, [x2, #CPU_XREG_OFFSET(16)]
>>> -	str	x18,      [x2, #CPU_XREG_OFFSET(18)]
>>> -
>>> -	ldp	x6, x7, [sp], #16	// x2, x3
>>> -	ldp	x4, x5, [sp], #16	// x0, x1
>>> -
>>> -	stp	x4, x5, [x2, #CPU_XREG_OFFSET(0)]
>>> -	stp	x6, x7, [x2, #CPU_XREG_OFFSET(2)]
>>> +	// x0: return code
>>> +	// x1: vcpu
>>> +	// x2-x29,lr: vcpu regs
>>> +	// vcpu x0-x1 on the stack
>>> +
>>> +	add	x1, x1, #VCPU_CONTEXT
>>> +
>>> +	// Store the guest regs x2 and x3
>>> +	stp	x2, x3,   [x1, #CPU_XREG_OFFSET(2)]
>>> +
>>> +	// Retrieve the guest regs x0-x1 from the stack
>>> +	ldp	x2, x3, [sp], #16	// x0, x1
>>> +
>>> +	// Store the guest regs x0-x1 and x4-x18
>>> +	stp	x2, x3,   [x1, #CPU_XREG_OFFSET(0)]
>>> +	stp	x4, x5,   [x1, #CPU_XREG_OFFSET(4)]
>>> +	stp	x6, x7,   [x1, #CPU_XREG_OFFSET(6)]
>>> +	stp	x8, x9,   [x1, #CPU_XREG_OFFSET(8)]
>>> +	stp	x10, x11, [x1, #CPU_XREG_OFFSET(10)]
>>> +	stp	x12, x13, [x1, #CPU_XREG_OFFSET(12)]
>>> +	stp	x14, x15, [x1, #CPU_XREG_OFFSET(14)]
>>> +	stp	x16, x17, [x1, #CPU_XREG_OFFSET(16)]
>>> +	str	x18,      [x1, #CPU_XREG_OFFSET(18)]
>>> +
>>> +	// Store the guest regs x19-x29, lr
>>> +	save_callee_saved_regs x1
>>>   
>>> -	save_callee_saved_regs x2
>>> +	// Restore the host_ctxt from the stack
>>> +	ldr	x2, [sp], #16
>>>   
>>> -	// Restore vcpu & host_ctxt from the stack
>>> -	// (preserving return code in x1)
>>> -	ldp	x0, x2, [sp], #16
>>>   	// Now restore the host regs
>>>   	restore_callee_saved_regs x2
>>>   
>>> -	mov	x0, x1
>>>   	ret
>>>   ENDPROC(__guest_exit)
>>>   
>>> diff --git a/arch/arm64/kvm/hyp/hyp-entry.S
> b/arch/arm64/kvm/hyp/hyp-entry.S
>>> index f6d9694..06e8b3b 100644
>>> --- a/arch/arm64/kvm/hyp/hyp-entry.S
>>> +++ b/arch/arm64/kvm/hyp/hyp-entry.S
>>> @@ -121,14 +121,15 @@ el1_trap:
>>>   	cmp	x2, #ESR_ELx_EC_FP_ASIMD
>>>   	b.eq	__fpsimd_guest_restore
>>>   
>>> -	mrs	x0, tpidr_el2
>>> -	mov	x1, #ARM_EXCEPTION_TRAP
>>> +	ldp     x2, x3, [sp], #16
>>> +	mrs	x1, tpidr_el2
>>> +	mov	x0, #ARM_EXCEPTION_TRAP
>>>   	b	__guest_exit
>>>   
>>>   el1_irq:
>>> -	save_x0_to_x3
> So the save_x0_to_x3 macro now only has one single user (and so does
> restore_x0_to_x3).  Should we consider inline it?

Sure, I'll change to inline in v3 patch.

>>> -	mrs	x0, tpidr_el2
>>> -	mov	x1, #ARM_EXCEPTION_IRQ
>>> +	stp     x0, x1, [sp, #-16]!
>>> +	mrs	x1, tpidr_el2
>>> +	mov	x0, #ARM_EXCEPTION_IRQ
>>>   	b	__guest_exit
>>>   
>>>   ENTRY(__hyp_do_panic)
>>> -- 
>>> Qualcomm Datacenter Technologies, Inc. on behalf of the Qualcomm
> Technologies, Inc.
>>> Qualcomm Technologies, Inc. is a member of the Code Aurora Forum, a
> Linux Foundation Collaborative Project.
> Thanks,
>
> 	M.

-- 
Shanker Donthineni
Qualcomm Datacenter Technologies, Inc. as an affiliate of Qualcomm Technologies, Inc.
Qualcomm Technologies, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project.

^ permalink raw reply	[flat|nested] 10+ messages in thread

* [PATCH v2] arm64: KVM: Save four instructions in __guest_enter/exit()
@ 2016-08-30 12:22       ` Shanker Donthineni
  0 siblings, 0 replies; 10+ messages in thread
From: Shanker Donthineni @ 2016-08-30 12:22 UTC (permalink / raw)
  To: linux-arm-kernel

Hi Marc,


On 08/30/2016 05:54 AM, Marc Zyngier wrote:
> On 30/08/16 10:55, Christoffer Dall wrote:
>> On Mon, Aug 29, 2016 at 10:51:14PM -0500, Shanker Donthineni wrote:
>>> We are doing an unnecessary stack push/pop operation when restoring
>>> the guest registers x0-x18 in __guest_enter(). This patch saves the
>>> two instructions by using x18 as a base register. No need to store
>>> the vcpu context pointer in stack because it is redundant, the same
>>> information is available in tpidr_el2. The function __guest_exit()
>>> prototype is simplified and caller pushes the regs x0-x1 to stack
>>> instead of regs x0-x3.
>>>
>>> Signed-off-by: Shanker Donthineni <shankerd@codeaurora.org>
>> This looks reasonable to me:
>>
>> Reviewed-by: Christoffer Dall <christoffer.dall@linaro.org>
>>
>> Unless Marc has any insight into this having a negative effect on ARM
>> CPUs, I'll go ahead an merge this.
> I've given it a go on Seattle, and couldn't observe any difference with
> the original code, which is pretty good news!
>
> I have some comments below, though:
>
>> -Christoffer
>>
>>> ---
>>> Changes since v1:
>>>    Incorporated Cristoffer suggestions.
>>>    __guest_exit prototype is changed to 'void __guest_exit(u64 reason,
> struct kvm_vcpu *vcpu)'.
>>>   arch/arm64/kvm/hyp/entry.S     | 101
> +++++++++++++++++++++--------------------
>>>   arch/arm64/kvm/hyp/hyp-entry.S |  11 +++--
>>>   2 files changed, 57 insertions(+), 55 deletions(-)
>>>
>>> diff --git a/arch/arm64/kvm/hyp/entry.S b/arch/arm64/kvm/hyp/entry.S
>>> index ce9e5e5..f70489a 100644
>>> --- a/arch/arm64/kvm/hyp/entry.S
>>> +++ b/arch/arm64/kvm/hyp/entry.S
>>> @@ -55,75 +55,76 @@
>>>    */
>>>   ENTRY(__guest_enter)
>>>   	// x0: vcpu
>>> -	// x1: host/guest context
>>> -	// x2-x18: clobbered by macros
>>> +	// x1: host context
>>> +	// x2-x17: clobbered by macros
>>> +	// x18: guest context
>>>   
>>>   	// Store the host regs
>>>   	save_callee_saved_regs x1
>>>   
>>> -	// Preserve vcpu & host_ctxt for use at exit time
>>> -	stp	x0, x1, [sp, #-16]!
>>> +	// Store the host_ctxt for use at exit time
>>> +	str	x1, [sp, #-16]!
>>>   
>>> -	add	x1, x0, #VCPU_CONTEXT
>>> +	add	x18, x0, #VCPU_CONTEXT
>>>   
>>> -	// Prepare x0-x1 for later restore by pushing them onto the stack
>>> -	ldp	x2, x3, [x1, #CPU_XREG_OFFSET(0)]
>>> -	stp	x2, x3, [sp, #-16]!
>>> +	// Restore guest regs x0-x17
>>> +	ldp	x0, x1,   [x18, #CPU_XREG_OFFSET(0)]
>>> +	ldp	x2, x3,   [x18, #CPU_XREG_OFFSET(2)]
>>> +	ldp	x4, x5,   [x18, #CPU_XREG_OFFSET(4)]
>>> +	ldp	x6, x7,   [x18, #CPU_XREG_OFFSET(6)]
>>> +	ldp	x8, x9,   [x18, #CPU_XREG_OFFSET(8)]
>>> +	ldp	x10, x11, [x18, #CPU_XREG_OFFSET(10)]
>>> +	ldp	x12, x13, [x18, #CPU_XREG_OFFSET(12)]
>>> +	ldp	x14, x15, [x18, #CPU_XREG_OFFSET(14)]
>>> +	ldp	x16, x17, [x18, #CPU_XREG_OFFSET(16)]
>>>   
>>> -	// x2-x18
>>> -	ldp	x2, x3,   [x1, #CPU_XREG_OFFSET(2)]
>>> -	ldp	x4, x5,   [x1, #CPU_XREG_OFFSET(4)]
>>> -	ldp	x6, x7,   [x1, #CPU_XREG_OFFSET(6)]
>>> -	ldp	x8, x9,   [x1, #CPU_XREG_OFFSET(8)]
>>> -	ldp	x10, x11, [x1, #CPU_XREG_OFFSET(10)]
>>> -	ldp	x12, x13, [x1, #CPU_XREG_OFFSET(12)]
>>> -	ldp	x14, x15, [x1, #CPU_XREG_OFFSET(14)]
>>> -	ldp	x16, x17, [x1, #CPU_XREG_OFFSET(16)]
>>> -	ldr	x18,      [x1, #CPU_XREG_OFFSET(18)]
>>> +	// Restore guest regs x19-x29, lr
>>> +	restore_callee_saved_regs x18
>>>   
>>> -	// x19-x29, lr
>>> -	restore_callee_saved_regs x1
>>> -
>>> -	// Last bits of the 64bit state
>>> -	ldp	x0, x1, [sp], #16
>>> +	// Restore guest reg x18
>>> +	ldr	x18,      [x18, #CPU_XREG_OFFSET(18)]
>>>   
>>>   	// Do not touch any register after this!
>>>   	eret
>>>   ENDPROC(__guest_enter)
>>>   
>>> +/*
>>> + * void __guest_exit(u64 exit_reason, struct kvm_vcpu *vcpu);
>>> + */
> I'm not sure this comment makes much sense as it stands. This is not a C
> function by any stretch of the imagination, but the continuation of
> __guest_enter. The calling convention is not the C one at all (see how
> the stack is involved), and caller-saved registers are going to be
> clobbered.

I'll remove this confusing comments.

>>>   ENTRY(__guest_exit)
>>> -	// x0: vcpu
>>> -	// x1: return code
>>> -	// x2-x3: free
>>> -	// x4-x29,lr: vcpu regs
>>> -	// vcpu x0-x3 on the stack
>>> -
>>> -	add	x2, x0, #VCPU_CONTEXT
>>> -
>>> -	stp	x4, x5,   [x2, #CPU_XREG_OFFSET(4)]
>>> -	stp	x6, x7,   [x2, #CPU_XREG_OFFSET(6)]
>>> -	stp	x8, x9,   [x2, #CPU_XREG_OFFSET(8)]
>>> -	stp	x10, x11, [x2, #CPU_XREG_OFFSET(10)]
>>> -	stp	x12, x13, [x2, #CPU_XREG_OFFSET(12)]
>>> -	stp	x14, x15, [x2, #CPU_XREG_OFFSET(14)]
>>> -	stp	x16, x17, [x2, #CPU_XREG_OFFSET(16)]
>>> -	str	x18,      [x2, #CPU_XREG_OFFSET(18)]
>>> -
>>> -	ldp	x6, x7, [sp], #16	// x2, x3
>>> -	ldp	x4, x5, [sp], #16	// x0, x1
>>> -
>>> -	stp	x4, x5, [x2, #CPU_XREG_OFFSET(0)]
>>> -	stp	x6, x7, [x2, #CPU_XREG_OFFSET(2)]
>>> +	// x0: return code
>>> +	// x1: vcpu
>>> +	// x2-x29,lr: vcpu regs
>>> +	// vcpu x0-x1 on the stack
>>> +
>>> +	add	x1, x1, #VCPU_CONTEXT
>>> +
>>> +	// Store the guest regs x2 and x3
>>> +	stp	x2, x3,   [x1, #CPU_XREG_OFFSET(2)]
>>> +
>>> +	// Retrieve the guest regs x0-x1 from the stack
>>> +	ldp	x2, x3, [sp], #16	// x0, x1
>>> +
>>> +	// Store the guest regs x0-x1 and x4-x18
>>> +	stp	x2, x3,   [x1, #CPU_XREG_OFFSET(0)]
>>> +	stp	x4, x5,   [x1, #CPU_XREG_OFFSET(4)]
>>> +	stp	x6, x7,   [x1, #CPU_XREG_OFFSET(6)]
>>> +	stp	x8, x9,   [x1, #CPU_XREG_OFFSET(8)]
>>> +	stp	x10, x11, [x1, #CPU_XREG_OFFSET(10)]
>>> +	stp	x12, x13, [x1, #CPU_XREG_OFFSET(12)]
>>> +	stp	x14, x15, [x1, #CPU_XREG_OFFSET(14)]
>>> +	stp	x16, x17, [x1, #CPU_XREG_OFFSET(16)]
>>> +	str	x18,      [x1, #CPU_XREG_OFFSET(18)]
>>> +
>>> +	// Store the guest regs x19-x29, lr
>>> +	save_callee_saved_regs x1
>>>   
>>> -	save_callee_saved_regs x2
>>> +	// Restore the host_ctxt from the stack
>>> +	ldr	x2, [sp], #16
>>>   
>>> -	// Restore vcpu & host_ctxt from the stack
>>> -	// (preserving return code in x1)
>>> -	ldp	x0, x2, [sp], #16
>>>   	// Now restore the host regs
>>>   	restore_callee_saved_regs x2
>>>   
>>> -	mov	x0, x1
>>>   	ret
>>>   ENDPROC(__guest_exit)
>>>   
>>> diff --git a/arch/arm64/kvm/hyp/hyp-entry.S
> b/arch/arm64/kvm/hyp/hyp-entry.S
>>> index f6d9694..06e8b3b 100644
>>> --- a/arch/arm64/kvm/hyp/hyp-entry.S
>>> +++ b/arch/arm64/kvm/hyp/hyp-entry.S
>>> @@ -121,14 +121,15 @@ el1_trap:
>>>   	cmp	x2, #ESR_ELx_EC_FP_ASIMD
>>>   	b.eq	__fpsimd_guest_restore
>>>   
>>> -	mrs	x0, tpidr_el2
>>> -	mov	x1, #ARM_EXCEPTION_TRAP
>>> +	ldp     x2, x3, [sp], #16
>>> +	mrs	x1, tpidr_el2
>>> +	mov	x0, #ARM_EXCEPTION_TRAP
>>>   	b	__guest_exit
>>>   
>>>   el1_irq:
>>> -	save_x0_to_x3
> So the save_x0_to_x3 macro now only has one single user (and so does
> restore_x0_to_x3).  Should we consider inline it?

Sure, I'll change to inline in v3 patch.

>>> -	mrs	x0, tpidr_el2
>>> -	mov	x1, #ARM_EXCEPTION_IRQ
>>> +	stp     x0, x1, [sp, #-16]!
>>> +	mrs	x1, tpidr_el2
>>> +	mov	x0, #ARM_EXCEPTION_IRQ
>>>   	b	__guest_exit
>>>   
>>>   ENTRY(__hyp_do_panic)
>>> -- 
>>> Qualcomm Datacenter Technologies, Inc. on behalf of the Qualcomm
> Technologies, Inc.
>>> Qualcomm Technologies, Inc. is a member of the Code Aurora Forum, a
> Linux Foundation Collaborative Project.
> Thanks,
>
> 	M.

-- 
Shanker Donthineni
Qualcomm Datacenter Technologies, Inc. as an affiliate of Qualcomm Technologies, Inc.
Qualcomm Technologies, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project.

^ permalink raw reply	[flat|nested] 10+ messages in thread

end of thread, other threads:[~2016-08-30 12:22 UTC | newest]

Thread overview: 10+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2016-08-30  3:51 [PATCH v2] arm64: KVM: Save four instructions in __guest_enter/exit() Shanker Donthineni
2016-08-30  3:51 ` Shanker Donthineni
2016-08-30  9:55 ` Christoffer Dall
2016-08-30  9:55   ` Christoffer Dall
2016-08-30  9:55   ` Christoffer Dall
2016-08-30 10:54   ` Marc Zyngier
2016-08-30 10:54     ` Marc Zyngier
2016-08-30 12:22     ` Shanker Donthineni
2016-08-30 12:22       ` Shanker Donthineni
2016-08-30 12:22       ` Shanker Donthineni

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