ARM: extend non-secure switch to also go into HYP mode

For the KVM and XEN hypervisors to be usable, we need to enter the
kernel in HYP mode. Now that we already are in non-secure state,
HYP mode switching is within short reach.

While doing the non-secure switch, we have to enable the HVC
instruction and setup the HYP mode HVBAR (while still secure).

The actual switch is done by dropping back from a HYP mode handler
without actually leaving HYP mode, so we introduce a new handler
routine in our new secure exception vector table.

In the assembly switching routine we save and restore the banked LR
and SP registers around the hypercall to do the actual HYP mode
switch.

The C routine first checks whether we are in HYP mode already and
also whether the virtualization extensions are available. It also
checks whether the HYP mode switch was finally successful.
The bootm command part only calls the new function after the
non-secure switch.

Signed-off-by: Andre Przywara <andre.przywara@linaro.org>

arch/arm/cpu/armv7/Makefile

@@ -20,7 +20,7 @@ ifneq ($(CONFIG_AM43XX)$(CONFIG_AM33XX)$(CONFIG_OMAP44XX)$(CONFIG_OMAP54XX)$(CON
 SOBJS	+= lowlevel_init.o
 endif
 
-ifneq ($(CONFIG_ARMV7_NONSEC),)
+ifneq ($(CONFIG_ARMV7_NONSEC)$(CONFIG_ARMV7_VIRT),)
 SOBJS	+= nonsec_virt.o
 COBJS	+= virt-v7.o
 endif

arch/arm/cpu/armv7/nonsec_virt.S

 /*
- * code for switching cores into non-secure state
+ * code for switching cores into non-secure state and into HYP mode
  *
  * Copyright (c) 2013	Andre Przywara <andre.przywara@linaro.org>
  *
@@ -28,15 +28,16 @@
 #include <asm/armv7.h>
 
 .arch_extension sec
+.arch_extension virt
 
-/* the vector table for secure state */
+/* the vector table for secure state and HYP mode */
 _monitor_vectors:
 	.word 0	/* reset */
 	.word 0 /* undef */
 	adr pc, _secure_monitor
 	.word 0
 	.word 0
-	.word 0
+	adr pc, _hyp_trap
 	.word 0
 	.word 0
 
@@ -53,10 +54,27 @@ _secure_monitor:
 	bic	r1, r1, #0x4e			@ clear IRQ, FIQ, EA, nET bits
 	orr	r1, r1, #0x31			@ enable NS, AW, FW bits
 
+#ifdef CONFIG_ARMV7_VIRT
+	mrc	p15, 0, r0, c0, c1, 1		@ read ID_PFR1
+	and	r0, r0, #CPUID_ARM_VIRT_MASK	@ mask virtualization bits
+	cmp	r0, #(1 << CPUID_ARM_VIRT_SHIFT)
+	orreq	r1, r1, #0x100			@ allow HVC instruction
+#endif
+
 	mcr	p15, 0, r1, c1, c1, 0		@ write SCR (with NS bit set)
 
+#ifdef CONFIG_ARMV7_VIRT
+	mrceq	p15, 0, r0, c12, c0, 1		@ get MVBAR value
+	mcreq	p15, 4, r0, c12, c0, 0		@ write HVBAR
+#endif
+
 	movs	pc, lr				@ return to non-secure SVC
 
+_hyp_trap:
+	mrs	lr, elr_hyp	@ for older asm: .byte 0x00, 0xe3, 0x0e, 0xe1
+	mov pc, lr				@ do no switch modes, but
+						@ return to caller
+
 /*
  * Secondary CPUs start here and call the code for the core specific parts
  * of the non-secure and HYP mode transition. The GIC distributor specific
@@ -71,9 +89,13 @@ ENTRY(_smp_pen)
 	mcr	p15, 0, r1, c12, c0, 0		@ set VBAR
 
 	bl	_nonsec_init
+	mov	r12, r0				@ save GICC address
+#ifdef CONFIG_ARMV7_VIRT
+	bl	_switch_to_hyp
+#endif
 
-	ldr	r1, [r0, #GICC_IAR]		@ acknowledge IPI
-	str	r1, [r0, #GICC_EOIR]		@ signal end of interrupt
+	ldr	r1, [r12, #GICC_IAR]		@ acknowledge IPI
+	str	r1, [r12, #GICC_EOIR]		@ signal end of interrupt
 
 	adr	r0, _smp_pen			@ do not use this address again
 	b	smp_waitloop			@ wait for IPIs, board specific
@@ -173,3 +195,14 @@ ENTRY(smp_waitloop)
 ENDPROC(smp_waitloop)
 .weak smp_waitloop
 #endif
+
+ENTRY(_switch_to_hyp)
+	mov	r0, lr
+	mov	r1, sp				@ save SVC copy of LR and SP
+	isb
+	hvc #0			 @ for older asm: .byte 0x70, 0x00, 0x40, 0xe1
+	mov	sp, r1
+	mov	lr, r0				@ restore SVC copy of LR and SP
+
+	bx	lr
+ENDPROC(_switch_to_hyp)

arch/arm/cpu/armv7/virt-v7.c

@@ -3,6 +3,7 @@
  * Andre Przywara, Linaro
  *
  * Routines to transition ARMv7 processors from secure into non-secure state
+ * and from non-secure SVC into HYP mode
  * needed to enable ARMv7 virtualization for current hypervisors
  *
  * See file CREDITS for list of people who contributed to this
@@ -31,6 +32,14 @@
 
 unsigned long gic_dist_addr;
 
+static unsigned int read_cpsr(void)
+{
+	unsigned int reg;
+
+	asm volatile ("mrs %0, cpsr\n" : "=r" (reg));
+	return reg;
+}
+
 static unsigned int read_id_pfr1(void)
 {
 	unsigned int reg;
@@ -90,6 +99,34 @@ void __weak smp_kick_all_cpus(void)
 	kick_secondary_cpus_gic(gic_dist_addr);
 }
 
+int armv7_switch_hyp(void)
+{
+	unsigned int reg;
+
+	/* check whether we are in HYP mode already */
+	if ((read_cpsr() & 0x1f) == 0x1a) {
+		debug("CPU already in HYP mode\n");
+		return 0;
+	}
+
+	/* check whether the CPU supports the virtualization extensions */
+	reg = read_id_pfr1();
+	if ((reg & CPUID_ARM_VIRT_MASK) != 1 << CPUID_ARM_VIRT_SHIFT) {
+		printf("HYP mode: Virtualization extensions not implemented.\n");
+		return -1;
+	}
+
+	/* call the HYP switching code on this CPU also */
+	_switch_to_hyp();
+
+	if ((read_cpsr() & 0x1F) != 0x1a) {
+		printf("HYP mode: switch not successful.\n");
+		return -1;
+	}
+
+	return 0;
+}
+
 int armv7_switch_nonsec(void)
 {
 	unsigned int reg;

arch/arm/include/asm/armv7.h

@@ -76,14 +76,16 @@ void v7_outer_cache_inval_all(void);
 void v7_outer_cache_flush_range(u32 start, u32 end);
 void v7_outer_cache_inval_range(u32 start, u32 end);
 
-#ifdef CONFIG_ARMV7_NONSEC
+#if defined(CONFIG_ARMV7_NONSEC) || defined(CONFIG_ARMV7_VIRT)
 
 int armv7_switch_nonsec(void);
+int armv7_switch_hyp(void);
 
 /* defined in assembly file */
 unsigned int _nonsec_init(void);
 void _smp_pen(void);
-#endif /* CONFIG_ARMV7_NONSEC */
+void _switch_to_hyp(void);
+#endif /* CONFIG_ARMV7_NONSEC || CONFIG_ARMV7_VIRT */
 
 #endif /* ! __ASSEMBLY__ */
 

arch/arm/lib/bootm.c

@@ -22,7 +22,7 @@
 #include <asm/bootm.h>
 #include <linux/compiler.h>
 
-#ifdef CONFIG_ARMV7_NONSEC
+#if defined(CONFIG_ARMV7_NONSEC) || defined(CONFIG_ARMV7_VIRT)
 #include <asm/armv7.h>
 #endif
 
@@ -189,8 +189,13 @@ static void do_nonsec_virt_switch(void)
 {
 #if defined(CONFIG_ARMV7_NONSEC) || defined(CONFIG_ARMV7_VIRT)
 	if (armv7_switch_nonsec() == 0)
+#ifdef CONFIG_ARMV7_VIRT
+		if (armv7_switch_hyp() == 0)
+			debug("entered HYP mode\n");
+#else
 		debug("entered non-secure state\n");
 #endif
+#endif
 }
 
 /* Subcommand: PREP */