KVM: arm64: Extract __do_hyp_init into a helper function

In preparation for adding a CPU entry point in nVHE hyp code, extract
most of __do_hyp_init hypervisor initialization code into a common
helper function. This will be invoked by the entry point to install KVM
on the newly booted CPU.

Signed-off-by: David Brazdil <dbrazdil@google.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20201202184122.26046-20-dbrazdil@google.com

arch/arm64/kvm/hyp/nvhe/hyp-init.S

@@ -68,17 +68,36 @@ __do_hyp_init:
 	mov	x0, #SMCCC_RET_NOT_SUPPORTED
 	eret
 
-1:	ldr	x0, [x1, #NVHE_INIT_TPIDR_EL2]
-	msr	tpidr_el2, x0
+1:	mov	x0, x1
+	mov	x4, lr
+	bl	___kvm_hyp_init
+	mov	lr, x4
 
-	ldr	x0, [x1, #NVHE_INIT_MAIR_EL2]
-	msr	mair_el2, x0
+	/* Hello, World! */
+	mov	x0, #SMCCC_RET_SUCCESS
+	eret
+SYM_CODE_END(__kvm_hyp_init)
+
+/*
+ * Initialize the hypervisor in EL2.
+ *
+ * Only uses x0..x3 so as to not clobber callee-saved SMCCC registers
+ * and leave x4 for the caller.
+ *
+ * x0: struct kvm_nvhe_init_params PA
+ */
+SYM_CODE_START_LOCAL(___kvm_hyp_init)
+	ldr	x1, [x0, #NVHE_INIT_TPIDR_EL2]
+	msr	tpidr_el2, x1
+
+	ldr	x1, [x0, #NVHE_INIT_STACK_HYP_VA]
+	mov	sp, x1
 
-	ldr	x0, [x1, #NVHE_INIT_STACK_HYP_VA]
-	mov	sp, x0
+	ldr	x1, [x0, #NVHE_INIT_MAIR_EL2]
+	msr	mair_el2, x1
 
-	ldr	x0, [x1, #NVHE_INIT_PGD_PA]
-	phys_to_ttbr x2, x0
+	ldr	x1, [x0, #NVHE_INIT_PGD_PA]
+	phys_to_ttbr x2, x1
 alternative_if ARM64_HAS_CNP
 	orr	x2, x2, #TTBR_CNP_BIT
 alternative_else_nop_endif
@@ -87,9 +106,9 @@ alternative_else_nop_endif
 	/*
 	 * Set the PS bits in TCR_EL2.
 	 */
-	ldr	x0, [x1, #NVHE_INIT_TCR_EL2]
-	tcr_compute_pa_size x0, #TCR_EL2_PS_SHIFT, x1, x2
-	msr	tcr_el2, x0
+	ldr	x1, [x0, #NVHE_INIT_TCR_EL2]
+	tcr_compute_pa_size x1, #TCR_EL2_PS_SHIFT, x2, x3
+	msr	tcr_el2, x1
 
 	isb
 
@@ -117,10 +136,8 @@ alternative_else_nop_endif
 	kimg_hyp_va x0, x1
 	msr	vbar_el2, x0
 
-	/* Hello, World! */
-	mov	x0, #SMCCC_RET_SUCCESS
-	eret
-SYM_CODE_END(__kvm_hyp_init)
+	ret
+SYM_CODE_END(___kvm_hyp_init)
 
 SYM_CODE_START(__kvm_handle_stub_hvc)
 	cmp	x0, #HVC_SOFT_RESTART