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ARM: 7445/1: mm: update CONTEXTIDR register to contain PID of current process

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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>
This commit is contained in:
Will Deacon 2012-07-06 15:43:03 +01:00 committed by Russell King
parent 27a5569dc6
commit 575320d625
4 changed files with 55 additions and 0 deletions
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9
arch/arm/Kconfig.debug
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@ -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

35
arch/arm/mm/context.c
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@ -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.

6
arch/arm/mm/proc-v6.S
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@ -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

5
arch/arm/mm/proc-v7-2level.S
View File

@ -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