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arm64: mm: update CONTEXTIDR register to contain PID of current process

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This patch is a port of 575320d62 ("ARM: 7445/1: mm: update CONTEXTIDR
register to contain PID of current process") from ARM that introduces a
new Kconfig option which, when enabled, causes the kernel to write the
PID of the current task into the CONTEXTIDR register 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.

Signed-off-by: Will Deacon <will.deacon@arm.com>
[catalin.marinas@arm.com: contextidr_thread_switch() moved to mmu_context.h]
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
This commit is contained in:
Will Deacon 2013-01-17 12:31:45 +00:00 committed by Catalin Marinas
parent 3a0310eb36
commit ec45d1cfd3
3 changed files with 26 additions and 1 deletions
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8
arch/arm64/Kconfig.debug
View File

@ -33,4 +33,12 @@ config EARLY_PRINTK
is assumed that the early console device has been initialised
by the boot loader prior to starting the Linux kernel.
config PID_IN_CONTEXTIDR
bool "Write the current PID to the CONTEXTIDR register"
help
Enabling this option causes the kernel to write the current PID to
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

15
arch/arm64/include/asm/mmu_context.h
View File

@ -35,6 +35,21 @@ extern unsigned int cpu_last_asid;
void __init_new_context(struct task_struct *tsk, struct mm_struct *mm);
void __new_context(struct mm_struct *mm);
#ifdef CONFIG_PID_IN_CONTEXTIDR
static inline void contextidr_thread_switch(struct task_struct *next)
{
asm(
" msr contextidr_el1, %0\n"
" isb"
:
: "r" (task_pid_nr(next)));
}
#else
static inline void contextidr_thread_switch(struct task_struct *next)
{
}
#endif
/*
* Set TTBR0 to empty_zero_page. No translations will be possible via TTBR0.
*/

4
arch/arm64/kernel/process.c
View File

@ -45,9 +45,10 @@
#include <asm/compat.h>
#include <asm/cacheflush.h>
#include <asm/fpsimd.h>
#include <asm/mmu_context.h>
#include <asm/processor.h>
#include <asm/stacktrace.h>
#include <asm/fpsimd.h>
static void setup_restart(void)
{
@ -319,6 +320,7 @@ struct task_struct *__switch_to(struct task_struct *prev,
/* the actual thread switch */
last = cpu_switch_to(prev, next);
contextidr_thread_switch(next);
return last;
}