arm64: add hypervisor stub

If booted in EL2, install an dummy hypervisor whose only purpose
is to be replaced by a full fledged one.

A minimal API allows to:
- obtain the current HYP vectors (__hyp_get_vectors)
- set new HYP vectors (__hyp_set_vectors)

Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

arch/arm64/include/asm/virt.h

@@ -33,6 +33,9 @@
  */
 extern u32 __boot_cpu_mode[2];
 
+void __hyp_set_vectors(phys_addr_t phys_vector_base);
+phys_addr_t __hyp_get_vectors(void);
+
 /* Reports the availability of HYP mode */
 static inline bool is_hyp_mode_available(void)
 {

arch/arm64/kernel/Makefile

@@ -8,7 +8,8 @@ AFLAGS_head.o		:= -DTEXT_OFFSET=$(TEXT_OFFSET)
 # Object file lists.
 arm64-obj-y		:= cputable.o debug-monitors.o entry.o irq.o fpsimd.o	\
 			   entry-fpsimd.o process.o ptrace.o setup.o signal.o	\
-			   sys.o stacktrace.o time.o traps.o io.o vdso.o
+			   sys.o stacktrace.o time.o traps.o io.o vdso.o	\
+			   hyp-stub.o
 
 arm64-obj-$(CONFIG_COMPAT)		+= sys32.o kuser32.o signal32.o 	\
 					   sys_compat.o

arch/arm64/kernel/head.S

@@ -185,6 +185,10 @@ ENTRY(el2_setup)
 	msr	hstr_el2, xzr			// Disable CP15 traps to EL2
 #endif
 
+	/* Hypervisor stub */
+	adr	x0, __hyp_stub_vectors
+	msr	vbar_el2, x0
+
 	/* spsr */
 	mov	x0, #(PSR_F_BIT | PSR_I_BIT | PSR_A_BIT | PSR_D_BIT |\
 		      PSR_MODE_EL1h)

arch/arm64/kernel/hyp-stub.S

@@ -0,0 +1,109 @@
+/*
+ * Hypervisor stub
+ *
+ * Copyright (C) 2012 ARM Ltd.
+ * Author:	Marc Zyngier <marc.zyngier@arm.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <linux/init.h>
+#include <linux/linkage.h>
+
+#include <asm/assembler.h>
+#include <asm/ptrace.h>
+#include <asm/virt.h>
+
+	.text
+	.align 11
+
+ENTRY(__hyp_stub_vectors)
+	ventry	el2_sync_invalid		// Synchronous EL2t
+	ventry	el2_irq_invalid			// IRQ EL2t
+	ventry	el2_fiq_invalid			// FIQ EL2t
+	ventry	el2_error_invalid		// Error EL2t
+
+	ventry	el2_sync_invalid		// Synchronous EL2h
+	ventry	el2_irq_invalid			// IRQ EL2h
+	ventry	el2_fiq_invalid			// FIQ EL2h
+	ventry	el2_error_invalid		// Error EL2h
+
+	ventry	el1_sync			// Synchronous 64-bit EL1
+	ventry	el1_irq_invalid			// IRQ 64-bit EL1
+	ventry	el1_fiq_invalid			// FIQ 64-bit EL1
+	ventry	el1_error_invalid		// Error 64-bit EL1
+
+	ventry	el1_sync_invalid		// Synchronous 32-bit EL1
+	ventry	el1_irq_invalid			// IRQ 32-bit EL1
+	ventry	el1_fiq_invalid			// FIQ 32-bit EL1
+	ventry	el1_error_invalid		// Error 32-bit EL1
+ENDPROC(__hyp_stub_vectors)
+
+	.align 11
+
+el1_sync:
+	mrs	x1, esr_el2
+	lsr	x1, x1, #26
+	cmp	x1, #0x16
+	b.ne	2f				// Not an HVC trap
+	cbz	x0, 1f
+	msr	vbar_el2, x0			// Set vbar_el2
+	b	2f
+1:	mrs	x0, vbar_el2			// Return vbar_el2
+2:	eret
+ENDPROC(el1_sync)
+
+.macro invalid_vector	label
+\label:
+	b \label
+ENDPROC(\label)
+.endm
+
+	invalid_vector	el2_sync_invalid
+	invalid_vector	el2_irq_invalid
+	invalid_vector	el2_fiq_invalid
+	invalid_vector	el2_error_invalid
+	invalid_vector	el1_sync_invalid
+	invalid_vector	el1_irq_invalid
+	invalid_vector	el1_fiq_invalid
+	invalid_vector	el1_error_invalid
+
+/*
+ * __hyp_set_vectors: Call this after boot to set the initial hypervisor
+ * vectors as part of hypervisor installation.  On an SMP system, this should
+ * be called on each CPU.
+ *
+ * x0 must be the physical address of the new vector table, and must be
+ * 2KB aligned.
+ *
+ * Before calling this, you must check that the stub hypervisor is installed
+ * everywhere, by waiting for any secondary CPUs to be brought up and then
+ * checking that is_hyp_mode_available() is true.
+ *
+ * If not, there is a pre-existing hypervisor, some CPUs failed to boot, or
+ * something else went wrong... in such cases, trying to install a new
+ * hypervisor is unlikely to work as desired.
+ *
+ * When you call into your shiny new hypervisor, sp_el2 will contain junk,
+ * so you will need to set that to something sensible at the new hypervisor's
+ * initialisation entry point.
+ */
+
+ENTRY(__hyp_get_vectors)
+	mov	x0, xzr
+	// fall through
+ENTRY(__hyp_set_vectors)
+	hvc	#0
+	ret
+ENDPROC(__hyp_get_vectors)
+ENDPROC(__hyp_set_vectors)