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authorWill Deacon <will.deacon@arm.com>2012-07-06 15:43:03 +0100
committerRussell King <rmk+kernel@arm.linux.org.uk>2012-07-09 17:41:10 +0100
commit575320d625d5b5eb115575a1f5e17af456e69577 (patch)
treedc44829a23c7eb3d6da82533853a3c9d304df6d7
parent27a5569dc66ecce06cb532542ddcd0b6da8783f6 (diff)
ARM: 7445/1: mm: update CONTEXTIDR register to contain PID of current process
This patch introduces a new Kconfig option which, when enabled, causes the kernel to write the PID of the current task into the PROCID field of the CONTEXTIDR on context switch. This is useful when analysing hardware trace, since writes to this register can be configured to emit an event into the trace stream. The thread notifier for writing the PID is deliberately kept separate from the ASID-writing code so that we can support newer processors using LPAE, where the ASID is stored in TTBR0. As such, the switch_mm code is updated to perform a read-modify-write sequence to ensure that we don't clobber the PID on CPUs using the classic 2-level page tables. Signed-off-by: Will Deacon <will.deacon@arm.com> Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
-rw-r--r--arch/arm/Kconfig.debug9
-rw-r--r--arch/arm/mm/context.c35
-rw-r--r--arch/arm/mm/proc-v6.S6
-rw-r--r--arch/arm/mm/proc-v7-2level.S5
4 files changed, 55 insertions, 0 deletions
diff --git a/arch/arm/Kconfig.debug b/arch/arm/Kconfig.debug
index 01a13414121..521e15bc640 100644
--- a/arch/arm/Kconfig.debug
+++ b/arch/arm/Kconfig.debug
@@ -369,4 +369,13 @@ config ARM_KPROBES_TEST
help
Perform tests of kprobes API and instruction set simulation.
+config PID_IN_CONTEXTIDR
+ bool "Write the current PID to the CONTEXTIDR register"
+ depends on CPU_COPY_V6
+ help
+ Enabling this option causes the kernel to write the current PID to
+ the PROCID field of the CONTEXTIDR register, at the expense of some
+ additional instructions during context switch. Say Y here only if you
+ are planning to use hardware trace tools with this kernel.
+
endmenu
diff --git a/arch/arm/mm/context.c b/arch/arm/mm/context.c
index 806cc4f6351..119bc52ab93 100644
--- a/arch/arm/mm/context.c
+++ b/arch/arm/mm/context.c
@@ -14,6 +14,7 @@
#include <linux/percpu.h>
#include <asm/mmu_context.h>
+#include <asm/thread_notify.h>
#include <asm/tlbflush.h>
static DEFINE_RAW_SPINLOCK(cpu_asid_lock);
@@ -48,6 +49,40 @@ void cpu_set_reserved_ttbr0(void)
}
#endif
+#ifdef CONFIG_PID_IN_CONTEXTIDR
+static int contextidr_notifier(struct notifier_block *unused, unsigned long cmd,
+ void *t)
+{
+ u32 contextidr;
+ pid_t pid;
+ struct thread_info *thread = t;
+
+ if (cmd != THREAD_NOTIFY_SWITCH)
+ return NOTIFY_DONE;
+
+ pid = task_pid_nr(thread->task) << ASID_BITS;
+ asm volatile(
+ " mrc p15, 0, %0, c13, c0, 1\n"
+ " bfi %1, %0, #0, %2\n"
+ " mcr p15, 0, %1, c13, c0, 1\n"
+ : "=r" (contextidr), "+r" (pid)
+ : "I" (ASID_BITS));
+ isb();
+
+ return NOTIFY_OK;
+}
+
+static struct notifier_block contextidr_notifier_block = {
+ .notifier_call = contextidr_notifier,
+};
+
+static int __init contextidr_notifier_init(void)
+{
+ return thread_register_notifier(&contextidr_notifier_block);
+}
+arch_initcall(contextidr_notifier_init);
+#endif
+
/*
* We fork()ed a process, and we need a new context for the child
* to run in.
diff --git a/arch/arm/mm/proc-v6.S b/arch/arm/mm/proc-v6.S
index 5900cd520e8..86b8b480634 100644
--- a/arch/arm/mm/proc-v6.S
+++ b/arch/arm/mm/proc-v6.S
@@ -107,6 +107,12 @@ ENTRY(cpu_v6_switch_mm)
mcr p15, 0, r2, c7, c5, 6 @ flush BTAC/BTB
mcr p15, 0, r2, c7, c10, 4 @ drain write buffer
mcr p15, 0, r0, c2, c0, 0 @ set TTB 0
+#ifdef CONFIG_PID_IN_CONTEXTIDR
+ mrc p15, 0, r2, c13, c0, 1 @ read current context ID
+ bic r2, r2, #0xff @ extract the PID
+ and r1, r1, #0xff
+ orr r1, r1, r2 @ insert into new context ID
+#endif
mcr p15, 0, r1, c13, c0, 1 @ set context ID
#endif
mov pc, lr
diff --git a/arch/arm/mm/proc-v7-2level.S b/arch/arm/mm/proc-v7-2level.S
index 42ac069c801..fd045e70639 100644
--- a/arch/arm/mm/proc-v7-2level.S
+++ b/arch/arm/mm/proc-v7-2level.S
@@ -46,6 +46,11 @@ ENTRY(cpu_v7_switch_mm)
#ifdef CONFIG_ARM_ERRATA_430973
mcr p15, 0, r2, c7, c5, 6 @ flush BTAC/BTB
#endif
+#ifdef CONFIG_PID_IN_CONTEXTIDR
+ mrc p15, 0, r2, c13, c0, 1 @ read current context ID
+ lsr r2, r2, #8 @ extract the PID
+ bfi r1, r2, #8, #24 @ insert into new context ID
+#endif
#ifdef CONFIG_ARM_ERRATA_754322
dsb
#endif