Commit c76c6c4e authored by Ard Biesheuvel's avatar Ard Biesheuvel Committed by Russell King (Oracle)
Browse files

ARM: 9294/2: vfp: Fix broken softirq handling with instrumentation enabled 

Commit 62b95a7b ("ARM: 9282/1: vfp: Manipulate task VFP state with
softirqs disabled") replaced the en/disable preemption calls inside the
VFP state handling code with en/disabling of soft IRQs, which is
necessary to allow kernel use of the VFP/SIMD unit when handling a soft
IRQ.

Unfortunately, when lockdep is enabled (or other instrumentation that
enables TRACE_IRQFLAGS), the disable path implemented in asm fails to
perform the lockdep and RCU related bookkeeping, resulting in spurious
warnings and other badness.

Set let's rework the VFP entry code a little bit so we can make the
local_bh_disable() call from C, with all the instrumentations that
happen to have been configured. Calling local_bh_enable() can be done
from asm, as it is a simple wrapper around __local_bh_enable_ip(), which
is always a callable function.

Link: https://lore.kernel.org/all/ZBBYCSZUJOWBg1s8@localhost.localdomain/



Fixes: 62b95a7b ("ARM: 9282/1: vfp: Manipulate task VFP state with softirqs disabled")
Signed-off-by: default avatarArd Biesheuvel <ardb@kernel.org>
Reviewed-by: default avatarLinus Walleij <linus.walleij@linaro.org>
Tested-by: default avatarGuenter Roeck <linux@roeck-us.net>
Signed-off-by: default avatarRussell King (Oracle) <rmk+kernel@armlinux.org.uk>
parent 3a2bdad0

arch/arm/include/asm/assembler.h

+0 −13
Original line number Diff line number Diff line
@@ -244,19 +244,6 @@ THUMB( fpreg .req r7 ) 
	.endm

#endif



	.macro	local_bh_disable, ti, tmp

	ldr	\tmp, [\ti, #TI_PREEMPT]

	add	\tmp, \tmp, #SOFTIRQ_DISABLE_OFFSET

	str	\tmp, [\ti, #TI_PREEMPT]

	.endm



	.macro	local_bh_enable_ti, ti, tmp

	get_thread_info \ti

	ldr	\tmp, [\ti, #TI_PREEMPT]

	sub	\tmp, \tmp, #SOFTIRQ_DISABLE_OFFSET

	str	\tmp, [\ti, #TI_PREEMPT]

	.endm



#define USERL(l, x...)				\

9999:	x;					\

	.pushsection __ex_table,"a";		\

arch/arm/vfp/entry.S

+1 −10
Original line number Diff line number Diff line
@@ -24,14 +24,5 @@ 
ENTRY(do_vfp)

	mov	r1, r10

	mov	r3, r9

 	ldr	r4, .LCvfp

	ldr	pc, [r4]		@ call VFP entry point

	b	vfp_entry

ENDPROC(do_vfp)
 


ENTRY(vfp_null_entry)

	ret	lr

ENDPROC(vfp_null_entry)



	.align	2

.LCvfp:

	.word	vfp_vector

arch/arm/vfp/vfphw.S

+6 −6
Original line number Diff line number Diff line
@@ -75,8 +75,6 @@ 
@  lr  = unrecognised instruction return address

@  IRQs enabled.

ENTRY(vfp_support_entry)

	local_bh_disable r1, r4



	ldr	r11, [r1, #TI_CPU]	@ CPU number

	add	r10, r1, #TI_VFPSTATE	@ r10 = workspace
@@ -179,9 +177,12 @@ vfp_hw_state_valid: 
					@ else it's one 32-bit instruction, so

					@ always subtract 4 from the following

					@ instruction address.

	local_bh_enable_ti r10, r4

	ret	r3			@ we think we have handled things



	mov	lr, r3			@ we think we have handled things

local_bh_enable_and_ret:

	adr	r0, .

	mov	r1, #SOFTIRQ_DISABLE_OFFSET

	b	__local_bh_enable_ip	@ tail call



look_for_VFP_exceptions:

	@ Check for synchronous or asynchronous exception
@@ -204,8 +205,7 @@ skip: 
	@ not recognised by VFP



	DBGSTR	"not VFP"

	local_bh_enable_ti r10, r4

	ret	lr

	b	local_bh_enable_and_ret



process_exception:

	DBGSTR	"bounce"

arch/arm/vfp/vfpmodule.c

+22 −5
Original line number Diff line number Diff line
@@ -32,10 +32,9 @@ 
/*

 * Our undef handlers (in entry.S)

 */

asmlinkage void vfp_support_entry(void);

asmlinkage void vfp_null_entry(void);

asmlinkage void vfp_support_entry(u32, void *, u32, u32);



asmlinkage void (*vfp_vector)(void) = vfp_null_entry;

static bool have_vfp __ro_after_init;



/*

 * Dual-use variable.
@@ -645,6 +644,25 @@ static int vfp_starting_cpu(unsigned int unused) 
	return 0;

}



/*

 * Entered with:

 *

 *  r0  = instruction opcode (32-bit ARM or two 16-bit Thumb)

 *  r1  = thread_info pointer

 *  r2  = PC value to resume execution after successful emulation

 *  r3  = normal "successful" return address

 *  lr  = unrecognised instruction return address

 */

asmlinkage void vfp_entry(u32 trigger, struct thread_info *ti, u32 resume_pc,

			  u32 resume_return_address)

{

	if (unlikely(!have_vfp))

		return;



	local_bh_disable();

	vfp_support_entry(trigger, ti, resume_pc, resume_return_address);

}



#ifdef CONFIG_KERNEL_MODE_NEON



static int vfp_kmode_exception(struct pt_regs *regs, unsigned int instr)
@@ -798,7 +816,6 @@ static int __init vfp_init(void) 
	vfpsid = fmrx(FPSID);

	barrier();

	unregister_undef_hook(&vfp_detect_hook);

	vfp_vector = vfp_null_entry;



	pr_info("VFP support v0.3: ");

	if (VFP_arch) {
@@ -883,7 +900,7 @@ static int __init vfp_init(void) 
				  "arm/vfp:starting", vfp_starting_cpu,

				  vfp_dying_cpu);



	vfp_vector = vfp_support_entry;

	have_vfp = true;



	thread_register_notifier(&vfp_notifier_block);

	vfp_pm_init();