ARM: KVM: Implement HVC_RESET_VECTORS stub hypercall in the init code

In order to restore HYP mode to its original condition, KVM currently
implements __kvm_hyp_reset(). As we're moving towards a hyp-stub
defined API, it becomes necessary to implement HVC_RESET_VECTORS.

This patch adds the HVC_RESET_VECTORS hypercall to the KVM init
code, which so far lacked any form of hypercall support.
Tested-by: Keerthy <j-keerthy@ti.com>
Acked-by: Russell King <rmk+kernel@armlinux.org.uk>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Christoffer Dall <cdall@linaro.org>

arch/arm/include/asm/virt.h

@@ -54,6 +54,7 @@ static inline void sync_boot_mode(void)
 
 void __hyp_set_vectors(unsigned long phys_vector_base);
 unsigned long __hyp_get_vectors(void);
+void __hyp_reset_vectors(void);
 #else
 #define __boot_cpu_mode	(SVC_MODE)
 #define sync_boot_mode()

arch/arm/kernel/hyp-stub.S

@@ -280,7 +280,7 @@ ENDPROC(__hyp_reset_vectors)
 #endif
 
 .align 5
-__hyp_stub_vectors:
+ENTRY(__hyp_stub_vectors)
 __hyp_stub_reset:	W(b)	.
 __hyp_stub_und:		W(b)	.
 __hyp_stub_svc:		W(b)	.

arch/arm/kvm/init.S

@@ -23,6 +23,7 @@
 #include <asm/kvm_asm.h>
 #include <asm/kvm_arm.h>
 #include <asm/kvm_mmu.h>
+#include <asm/virt.h>
 
 /********************************************************************
  * Hypervisor initialization
@@ -39,6 +40,10 @@
  * - Setup the page tables
  * - Enable the MMU
  * - Profit! (or eret, if you only care about the code).
+ *
+ * Another possibility is to get a HYP stub hypercall.
+ * We discriminate between the two by checking if r0 contains a value
+ * that is less than HVC_STUB_HCALL_NR.
  */
 
 	.text
@@ -58,6 +63,10 @@ __kvm_hyp_init:
 	W(b)	.
 
 __do_hyp_init:
+	@ Check for a stub hypercall
+	cmp	r0, #HVC_STUB_HCALL_NR
+	blo	__kvm_handle_stub_hvc
+
 	@ Set stack pointer
 	mov	sp, r0
 
@@ -112,19 +121,31 @@ __do_hyp_init:
 
 	eret
 
-	@ r0 : stub vectors address
+ENTRY(__kvm_handle_stub_hvc)
+	cmp	r0, #HVC_RESET_VECTORS
+	bne	1f
 ENTRY(__kvm_hyp_reset)
 	/* We're now in idmap, disable MMU */
 	mrc	p15, 4, r1, c1, c0, 0	@ HSCTLR
-	ldr	r2, =(HSCTLR_M | HSCTLR_A | HSCTLR_C | HSCTLR_I)
-	bic	r1, r1, r2
+	ldr	r0, =(HSCTLR_M | HSCTLR_A | HSCTLR_C | HSCTLR_I)
+	bic	r1, r1, r0
 	mcr	p15, 4, r1, c1, c0, 0	@ HSCTLR
 
-	/* Install stub vectors */
-	mcr	p15, 4, r0, c12, c0, 0	@ HVBAR
-	isb
+	/*
+	 * Install stub vectors, using ardb's VA->PA trick.
+	 */
+0:	adr	r0, 0b					@ PA(0)
+	movw	r1, #:lower16:__hyp_stub_vectors - 0b   @ VA(stub) - VA(0)
+	movt	r1, #:upper16:__hyp_stub_vectors - 0b
+	add	r1, r1, r0				@ PA(stub)
+	mcr	p15, 4, r1, c12, c0, 0	@ HVBAR
+	b	exit
+
+1:	ldr	r0, =HVC_STUB_ERR
 
+exit:
 	eret
+ENDPROC(__kvm_handle_stub_hvc)
 ENDPROC(__kvm_hyp_reset)
 
 	.ltorg