ARM: 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 code, so that we can easily support newer processors (A15
onwards) which store the ASID 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 older CPUs.
Change-Id: I7236834cf4b5e984c9d9f24ba6b872078c2b936f
Cc: Wolfgang Betz <wolfgang.betz@st.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Jeff Ohlstein <johlstei@codeaurora.org>
diff --git a/arch/arm/Kconfig.debug b/arch/arm/Kconfig.debug
index 81cbe40..8d3592e 100644
--- a/arch/arm/Kconfig.debug
+++ b/arch/arm/Kconfig.debug
@@ -129,4 +129,13 @@
The uncompressor code port configuration is now handled
by CONFIG_S3C_LOWLEVEL_UART_PORT.
+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 93aac06..14536f6 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);
@@ -22,6 +23,66 @@
DEFINE_PER_CPU(struct mm_struct *, current_mm);
#endif
+static void write_contextidr(u32 contextidr)
+{
+ asm("mcr p15, 0, %0, c13, c0, 1" : : "r" (contextidr));
+ isb();
+}
+
+#ifdef CONFIG_PID_IN_CONTEXTIDR
+static u32 read_contextidr(void)
+{
+ u32 contextidr;
+ asm("mrc p15, 0, %0, c13, c0, 1" : "=r" (contextidr));
+ return contextidr;
+}
+
+static int contextidr_notifier(struct notifier_block *unused, unsigned long cmd,
+ void *t)
+{
+ unsigned long flags;
+ u32 contextidr;
+ pid_t pid;
+ struct thread_info *thread = t;
+
+ if (cmd != THREAD_NOTIFY_SWITCH)
+ return NOTIFY_DONE;
+
+ pid = task_pid_nr(thread->task);
+ local_irq_save(flags);
+ contextidr = read_contextidr();
+ contextidr &= ~ASID_MASK;
+ contextidr |= pid << ASID_BITS;
+ write_contextidr(contextidr);
+ local_irq_restore(flags);
+
+ 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);
+
+static void set_asid(unsigned int asid)
+{
+ u32 contextidr = read_contextidr();
+ contextidr &= ASID_MASK;
+ contextidr |= asid & ~ASID_MASK;
+ write_contextidr(contextidr);
+}
+#else
+static void set_asid(unsigned int asid)
+{
+ write_contextidr(asid);
+}
+#endif
+
/*
* We fork()ed a process, and we need a new context for the child
* to run in. We reserve version 0 for initial tasks so we will
@@ -37,8 +98,7 @@
static void flush_context(void)
{
/* set the reserved ASID before flushing the TLB */
- asm("mcr p15, 0, %0, c13, c0, 1\n" : : "r" (0));
- isb();
+ set_asid(0);
local_flush_tlb_all();
if (icache_is_vivt_asid_tagged()) {
__flush_icache_all();
@@ -99,8 +159,7 @@
set_mm_context(mm, asid);
/* set the new ASID */
- asm("mcr p15, 0, %0, c13, c0, 1\n" : : "r" (mm->context.id));
- isb();
+ set_asid(mm->context.id);
}
#else
diff --git a/arch/arm/mm/proc-v6.S b/arch/arm/mm/proc-v6.S
index 1d2b845..0fb3106 100644
--- a/arch/arm/mm/proc-v6.S
+++ b/arch/arm/mm/proc-v6.S
@@ -99,6 +99,12 @@
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 the PID into r1
+#endif
mcr p15, 0, r1, c13, c0, 1 @ set context ID
#endif
mov pc, lr
diff --git a/arch/arm/mm/proc-v7.S b/arch/arm/mm/proc-v7.S
index 5943005..de65c4b 100644
--- a/arch/arm/mm/proc-v7.S
+++ b/arch/arm/mm/proc-v7.S
@@ -124,6 +124,12 @@
#ifdef CONFIG_ARM_ERRATA_754322
dsb
#endif
+#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 the PID into r1
+#endif
mcr p15, 0, r2, c13, c0, 1 @ set reserved context ID
isb
1: mcr p15, 0, r0, c2, c0, 0 @ set TTB 0