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Commit 575320d6 authored by Will Deacon's avatar Will Deacon Committed by Russell King
Browse files

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: default avatarWill Deacon <will.deacon@arm.com>
Signed-off-by: default avatarRussell King <rmk+kernel@arm.linux.org.uk>
parent 27a5569d

arch/arm/Kconfig.debug

+9 −0
Original line number Diff line number Diff line
@@ -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

arch/arm/mm/context.c

+35 −0
Original line number Diff line number Diff line
@@ -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.

arch/arm/mm/proc-v6.S

+6 −0
Original line number Diff line number Diff line
@@ -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

arch/arm/mm/proc-v7-2level.S

+5 −0
Original line number Diff line number Diff line
@@ -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