ARM: soft-reboot into same mode that we entered the kernel

When we soft-reboot (eg, kexec) from one kernel into the next, we need
to ensure that we enter the new kernel in the same processor mode as
when we were entered, so that (eg) the new kernel can install its own
hypervisor - the old kernel's hypervisor will have been overwritten.

In order to do this, we need to pass a flag to cpu_reset() so it knows
what to do, and we need to modify the kernel's own hypervisor stub to
allow it to handle a soft-reboot.

As we are always guaranteed to install our own hypervisor if we're
entered in HYP32 mode, and KVM will have moved itself out of the way
on kexec/normal reboot, we can assume that our hypervisor is in place
when we want to kexec, so changing our hypervisor API should not be a
problem.

Tested-by: Keerthy <j-keerthy@ti.com>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Christoffer Dall <cdall@linaro.org>

4 files changed, 28 insertions, 8 deletions

diff --git a/arch/arm/include/asm/proc-fns.h b/arch/arm/include/asm/proc-fns.h
index 8877ad5ffe10..f2e1af45bd6f 100644
--- a/arch/arm/include/asm/proc-fns.h
+++ b/arch/arm/include/asm/proc-fns.h
@@ -43,7 +43,7 @@ extern struct processor {
         /*
          * Special stuff for a reset
          */
-        void (*reset)(unsigned long addr) __attribute__((noreturn));
+        void (*reset)(unsigned long addr, bool hvc) __attribute__((noreturn));
         /*
          * Idle the processor
          */
@@ -88,7 +88,7 @@ extern void cpu_set_pte_ext(pte_t *ptep, pte_t pte);
 #else
 extern void cpu_set_pte_ext(pte_t *ptep, pte_t pte, unsigned int ext);
 #endif
-extern void cpu_reset(unsigned long addr) __attribute__((noreturn));
+extern void cpu_reset(unsigned long addr, bool hvc) __attribute__((noreturn));
 
 /* These three are private to arch/arm/kernel/suspend.c */
 extern void cpu_do_suspend(void *);
diff --git a/arch/arm/kernel/hyp-stub.S b/arch/arm/kernel/hyp-stub.S
index f3e9ba5fb642..82915231c6f8 100644
--- a/arch/arm/kernel/hyp-stub.S
+++ b/arch/arm/kernel/hyp-stub.S
@@ -24,6 +24,7 @@
 
 #define HVC_GET_VECTORS 0
 #define HVC_SET_VECTORS 1
+#define HVC_SOFT_RESTART 2
 
 #ifndef ZIMAGE
 /*
@@ -215,6 +216,10 @@ __hyp_stub_do_trap:
         mcr     p15, 4, r1, c12, c0, 0  @ set HVBAR
         b       __hyp_stub_exit
 
+1:      teq     r0, #HVC_SOFT_RESTART
+        bne     1f
+        bx      r3
+
 1:      mov     r0, #-1
 
 __hyp_stub_exit:
@@ -256,6 +261,14 @@ ENTRY(__hyp_set_vectors)
         ret     lr
 ENDPROC(__hyp_set_vectors)
 
+ENTRY(__hyp_soft_restart)
+        mov     r3, r0
+        mov     r0, #HVC_SOFT_RESTART
+        __HVC(0)
+        mov     r0, r3
+        ret     lr
+ENDPROC(__hyp_soft_restart)
+
 #ifndef ZIMAGE
 .align 2
 .L__boot_cpu_mode_offset:
diff --git a/arch/arm/kernel/reboot.c b/arch/arm/kernel/reboot.c
index 3fa867a2aae6..3b2aa9a9fe26 100644
--- a/arch/arm/kernel/reboot.c
+++ b/arch/arm/kernel/reboot.c
@@ -12,10 +12,11 @@
 
 #include <asm/cacheflush.h>
 #include <asm/idmap.h>
+#include <asm/virt.h>
 
 #include "reboot.h"
 
-typedef void (*phys_reset_t)(unsigned long);
+typedef void (*phys_reset_t)(unsigned long, bool);
 
 /*
  * Function pointers to optional machine specific functions
@@ -51,7 +52,9 @@ static void __soft_restart(void *addr)
 
         /* Switch to the identity mapping. */
         phys_reset = (phys_reset_t)virt_to_idmap(cpu_reset);
-        phys_reset((unsigned long)addr);
+
+        /* original stub should be restored by kvm */
+        phys_reset((unsigned long)addr, is_hyp_mode_available());
 
         /* Should never get here. */
         BUG();
diff --git a/arch/arm/mm/proc-v7.S b/arch/arm/mm/proc-v7.S
index d00d52c9de3e..1846ca4255d0 100644
--- a/arch/arm/mm/proc-v7.S
+++ b/arch/arm/mm/proc-v7.S
@@ -53,11 +53,15 @@ ENDPROC(cpu_v7_proc_fin)
         .align  5
         .pushsection    .idmap.text, "ax"
 ENTRY(cpu_v7_reset)
-        mrc     p15, 0, r1, c1, c0, 0           @ ctrl register
-        bic     r1, r1, #0x1                    @ ...............m
- THUMB( bic     r1, r1, #1 << 30 )              @ SCTLR.TE (Thumb exceptions)
-        mcr     p15, 0, r1, c1, c0, 0           @ disable MMU
+        mrc     p15, 0, r2, c1, c0, 0           @ ctrl register
+        bic     r2, r2, #0x1                    @ ...............m
+ THUMB( bic     r2, r2, #1 << 30 )              @ SCTLR.TE (Thumb exceptions)
+        mcr     p15, 0, r2, c1, c0, 0           @ disable MMU
         isb
+#ifdef CONFIG_ARM_VIRT_EXT
+        teq     r1, #0
+        bne     __hyp_soft_restart
+#endif
         bx      r0
 ENDPROC(cpu_v7_reset)
         .popsection