ARM: domains: switch to keeping domain value in register

Rather than modifying both the domain access control register and our
per-thread copy, modify only the domain access control register, and
use the per-thread copy to save and restore the register over context
switches.  We can also avoid the explicit initialisation of the
init thread_info structure.

This allows us to avoid needing to gain access to the thread information
at the uaccess control sites.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

4 files changed, 27 insertions, 11 deletions

diff --git a/arch/arm/include/asm/domain.h b/arch/arm/include/asm/domain.h
index 6ddbe446425e..7f2941905714 100644
--- a/arch/arm/include/asm/domain.h
+++ b/arch/arm/include/asm/domain.h
@@ -59,6 +59,17 @@
 
 #ifndef __ASSEMBLY__
 
+static inline unsigned int get_domain(void)
+{
+        unsigned int domain;
+
+        asm(
+        "mrc    p15, 0, %0, c3, c0      @ get domain"
+         : "=r" (domain));
+
+        return domain;
+}
+
 #ifdef CONFIG_CPU_USE_DOMAINS
 static inline void set_domain(unsigned val)
 {
@@ -70,11 +81,10 @@ static inline void set_domain(unsigned val)
 
 #define modify_domain(dom,type)                                 \
         do {                                                    \
-        struct thread_info *thread = current_thread_info();     \
-        unsigned int domain = thread->cpu_domain;               \
-        domain &= ~domain_val(dom, DOMAIN_MANAGER);             \
-        thread->cpu_domain = domain | domain_val(dom, type);    \
-        set_domain(thread->cpu_domain);                         \
+                unsigned int domain = get_domain();             \
+                domain &= ~domain_val(dom, DOMAIN_MANAGER);     \
+                domain = domain | domain_val(dom, type);        \
+                set_domain(domain);                             \
         } while (0)
 
 #else
diff --git a/arch/arm/include/asm/thread_info.h b/arch/arm/include/asm/thread_info.h
index bd32eded3e50..0a0aec410d8c 100644
--- a/arch/arm/include/asm/thread_info.h
+++ b/arch/arm/include/asm/thread_info.h
@@ -74,9 +74,6 @@ struct thread_info {
         .flags          = 0,                                            \
         .preempt_count  = INIT_PREEMPT_COUNT,                           \
         .addr_limit     = KERNEL_DS,                                    \
-        .cpu_domain     = domain_val(DOMAIN_USER, DOMAIN_MANAGER) |     \
-                          domain_val(DOMAIN_KERNEL, DOMAIN_MANAGER) |   \
-                          domain_val(DOMAIN_IO, DOMAIN_CLIENT),         \
 }
 
 #define init_thread_info        (init_thread_union.thread_info)
diff --git a/arch/arm/kernel/entry-armv.S b/arch/arm/kernel/entry-armv.S
index 7dac3086e361..d19adcf6c580 100644
--- a/arch/arm/kernel/entry-armv.S
+++ b/arch/arm/kernel/entry-armv.S
@@ -770,6 +770,8 @@ ENTRY(__switch_to)
         ldr     r4, [r2, #TI_TP_VALUE]
         ldr     r5, [r2, #TI_TP_VALUE + 4]
 #ifdef CONFIG_CPU_USE_DOMAINS
+        mrc     p15, 0, r6, c3, c0, 0           @ Get domain register
+        str     r6, [r1, #TI_CPU_DOMAIN]        @ Save old domain register
         ldr     r6, [r2, #TI_CPU_DOMAIN]
 #endif
         switch_tls r1, r4, r5, r3, r7
diff --git a/arch/arm/kernel/process.c b/arch/arm/kernel/process.c
index f192a2a41719..e722f9b3c9b1 100644
--- a/arch/arm/kernel/process.c
+++ b/arch/arm/kernel/process.c
@@ -146,10 +146,9 @@ void __show_regs(struct pt_regs *regs)
                 buf[0] = '\0';
 #ifdef CONFIG_CPU_CP15_MMU
                 {
-                        unsigned int transbase, dac;
+                        unsigned int transbase, dac = get_domain();
                         asm("mrc p15, 0, %0, c2, c0\n\t"
-                            "mrc p15, 0, %1, c3, c0\n"
-                            : "=r" (transbase), "=r" (dac));
+                            : "=r" (transbase));
                         snprintf(buf, sizeof(buf), "  Table: %08x  DAC: %08x",
                                 transbase, dac);
                 }
@@ -210,6 +209,14 @@ copy_thread(unsigned long clone_flags, unsigned long stack_start,
 
         memset(&thread->cpu_context, 0, sizeof(struct cpu_context_save));
 
+        /*
+         * Copy the initial value of the domain access control register
+         * from the current thread: thread->addr_limit will have been
+         * copied from the current thread via setup_thread_stack() in
+         * kernel/fork.c
+         */
+        thread->cpu_domain = get_domain();
+
         if (likely(!(p->flags & PF_KTHREAD))) {
                 *childregs = *current_pt_regs();
                 childregs->ARM_r0 = 0;