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Message-Id: <1472609312-569-1-git-send-email-shankerd@codeaurora.org>
Date: Tue, 30 Aug 2016 21:08:32 -0500
From: Shanker Donthineni <shankerd@...eaurora.org>
To: Marc Zyngier <marc.zyngier@....com>,
Christoffer Dall <christoffer.dall@...aro.org>,
linux-kernel <linux-kernel@...r.kernel.org>,
linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
kvmarm <kvmarm@...ts.cs.columbia.edu>
Cc: Paolo Bonzini <pbonzini@...hat.com>,
Will Deacon <will.deacon@....com>,
Catalin Marinas <catalin.marinas@....com>,
James Morse <james.morse@....com>,
Vikram Sethi <vikrams@...eaurora.org>,
Shanker Donthineni <shankerd@...eaurora.org>
Subject: [PATCH v3] arm64: KVM: Optimize __guest_enter/exit() to save a few instructions
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()
calling convention is slightly modified, caller only pushes the regs
x0-x1 to stack instead of regs x0-x3.
Signed-off-by: Shanker Donthineni <shankerd@...eaurora.org>
Reviewed-by: Christoffer Dall <christoffer.dall@...aro.org>
---
Tested this patch using the Qualcomm QDF24XXX platform.
Changes since v2:
Removed macros save_x0_to_x3/restore_x0_to_x3.
Modified el1_sync() to use regs x0 and x1.
Edited commit text.
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 | 37 ++++++---------
2 files changed, 63 insertions(+), 75 deletions(-)
diff --git a/arch/arm64/kvm/hyp/entry.S b/arch/arm64/kvm/hyp/entry.S
index ce9e5e5..3967c231 100644
--- a/arch/arm64/kvm/hyp/entry.S
+++ b/arch/arm64/kvm/hyp/entry.S
@@ -55,79 +55,78 @@
*/
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)]
-
- // x19-x29, lr
- restore_callee_saved_regs x1
-
- // Last bits of the 64bit state
- ldp x0, x1, [sp], #16
+ // Restore guest regs x19-x29, lr
+ restore_callee_saved_regs x18
+
+ // Restore guest reg x18
+ ldr x18, [x18, #CPU_XREG_OFFSET(18)]
// Do not touch any register after this!
eret
ENDPROC(__guest_enter)
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)
ENTRY(__fpsimd_guest_restore)
+ stp x2, x3, [sp, #-16]!
stp x4, lr, [sp, #-16]!
alternative_if_not ARM64_HAS_VIRT_HOST_EXTN
diff --git a/arch/arm64/kvm/hyp/hyp-entry.S b/arch/arm64/kvm/hyp/hyp-entry.S
index f6d9694..d6cae542 100644
--- a/arch/arm64/kvm/hyp/hyp-entry.S
+++ b/arch/arm64/kvm/hyp/hyp-entry.S
@@ -27,16 +27,6 @@
.text
.pushsection .hyp.text, "ax"
-.macro save_x0_to_x3
- stp x0, x1, [sp, #-16]!
- stp x2, x3, [sp, #-16]!
-.endm
-
-.macro restore_x0_to_x3
- ldp x2, x3, [sp], #16
- ldp x0, x1, [sp], #16
-.endm
-
.macro do_el2_call
/*
* Shuffle the parameters before calling the function
@@ -79,23 +69,23 @@ ENTRY(__kvm_hyp_teardown)
ENDPROC(__kvm_hyp_teardown)
el1_sync: // Guest trapped into EL2
- save_x0_to_x3
+ stp x0, x1, [sp, #-16]!
alternative_if_not ARM64_HAS_VIRT_HOST_EXTN
mrs x1, esr_el2
alternative_else
mrs x1, esr_el1
alternative_endif
- lsr x2, x1, #ESR_ELx_EC_SHIFT
+ lsr x0, x1, #ESR_ELx_EC_SHIFT
- cmp x2, #ESR_ELx_EC_HVC64
+ cmp x0, #ESR_ELx_EC_HVC64
b.ne el1_trap
- mrs x3, vttbr_el2 // If vttbr is valid, the 64bit guest
- cbnz x3, el1_trap // called HVC
+ mrs x1, vttbr_el2 // If vttbr is valid, the 64bit guest
+ cbnz x1, el1_trap // called HVC
/* Here, we're pretty sure the host called HVC. */
- restore_x0_to_x3
+ ldp x0, x1, [sp], #16
cmp x0, #HVC_GET_VECTORS
b.ne 1f
@@ -113,22 +103,21 @@ alternative_endif
el1_trap:
/*
- * x1: ESR
- * x2: ESR_EC
+ * x0: ESR_EC
*/
/* Guest accessed VFP/SIMD registers, save host, restore Guest */
- cmp x2, #ESR_ELx_EC_FP_ASIMD
+ cmp x0, #ESR_ELx_EC_FP_ASIMD
b.eq __fpsimd_guest_restore
- mrs x0, tpidr_el2
- mov x1, #ARM_EXCEPTION_TRAP
+ 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.
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