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Commit 68381b2b authored by Shanker Donthineni's avatar Shanker Donthineni Committed by Christoffer Dall
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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: default avatarShanker Donthineni <shankerd@codeaurora.org>
Reviewed-by: default avatarChristoffer Dall <christoffer.dall@linaro.org>
Signed-off-by: default avatarChristoffer Dall <christoffer.dall@linaro.org>
parent 1fe00098

arch/arm64/kvm/hyp/entry.S

+50 −51
Original line number Diff line number Diff line
@@ -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

arch/arm64/kvm/hyp/hyp-entry.S

+13 −24
Original line number Diff line number Diff line
@@ -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)