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Message-ID: <5415376F.10302@linaro.org>
Date: Sun, 14 Sep 2014 07:36:31 +0100
From: Daniel Thompson <daniel.thompson@...aro.org>
To: Russell King - ARM Linux <linux@....linux.org.uk>
CC: linaro-kernel@...ts.linaro.org, patches@...aro.org,
Catalin Marinas <catalin.marinas@....com>,
linux-kernel@...r.kernel.org, John Stultz <john.stultz@...aro.org>,
Thomas Gleixner <tglx@...utronix.de>,
Sumit Semwal <sumit.semwal@...aro.org>,
linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 3.17-rc4 v5 2/6] arm: fiq: Replace default FIQ handler
On 12/09/14 18:23, Russell King - ARM Linux wrote:
> On Fri, Sep 12, 2014 at 06:19:08PM +0100, Russell King - ARM Linux wrote:
>> On Fri, Sep 12, 2014 at 06:14:04PM +0100, Russell King - ARM Linux wrote:
>>> On Thu, Sep 11, 2014 at 12:31:14PM +0100, Daniel Thompson wrote:
>>>> This patch introduces a new default FIQ handler that is structured in a
>>>> similar way to the existing ARM exception handler and result in the FIQ
>>>> being handled by C code running on the SVC stack (despite this code run
>>>> in the FIQ handler is subject to severe limitations with respect to
>>>> locking making normal interaction with the kernel impossible).
>>>>
>>>> This default handler allows concepts that on x86 would be handled using
>>>> NMIs to be realized on ARM.
>>>
>>> Okay, lastly... I sent you my version of this change, which contained
>>> the changes I've detailed in the previous three emails, which are absent
>>> from your version.
>>>
>>> However, you've taken on board the "trace" thing to svc_entry, and
>>> renamed it to "call_trace".
>>>
>>> Now if I add this to usr_entry, "call_trace" doesn't make any sense,
>>> nor does the .if/.endif placement because it's not just trace_hardirqs_off
>>> which needs to be disabled there, but also ct_user_exit as well.
>>>
>>> I'm beginning to wonder why I tried to be nice here... it would've been
>>> a lot faster for me to take your patch, make my own changes and commit
>>> that instead.
>>>
>>> Frustrated.
>>
>> And another thing you're missing are the updates to arch/arm/kernel/fiq.c
>> to ensure that the FIQ registers are preserved when we restore this new
>> default FIQ handler.
>
> Right, here's my remaining delta from your patch addressing all the points
> from the last five emails. If you have any disagreements with any of these
> changes, then please discuss rather than choosing to ignore them.
Thanks for the diff.
> 107e32b0b4ef5fa4191c9fc8415ca172b886e958
> diff --git a/arch/arm/kernel/entry-armv.S b/arch/arm/kernel/entry-armv.S
> index 0c70fee9a7c9..3f6293ce0f2d 100644
> --- a/arch/arm/kernel/entry-armv.S
> +++ b/arch/arm/kernel/entry-armv.S
> @@ -146,7 +146,7 @@ ENDPROC(__und_invalid)
> #define SPFIX(code...)
> #endif
>
> - .macro svc_entry, stack_hole=0, call_trace=1
> + .macro svc_entry, stack_hole=0, trace=1
> UNWIND(.fnstart )
> UNWIND(.save {r0 - pc} )
> sub sp, sp, #(S_FRAME_SIZE + \stack_hole - 4)
> @@ -182,11 +182,11 @@ ENDPROC(__und_invalid)
> @
> stmia r7, {r2 - r6}
>
> + .if \trace
> #ifdef CONFIG_TRACE_IRQFLAGS
> - .if \call_trace
> bl trace_hardirqs_off
> - .endif
> #endif
> + .endif
> .endm
>
> .align 5
> @@ -298,7 +298,7 @@ ENDPROC(__pabt_svc)
>
> .align 5
> __fiq_svc:
> - svc_entry 0, 0
> + svc_entry trace=0
> mov r0, sp @ struct pt_regs *regs
> bl handle_fiq_as_nmi
> svc_exit_via_fiq
> @@ -326,7 +326,7 @@ ENDPROC(__fiq_svc)
> @
> .align 5
> __fiq_abt:
> - svc_entry 0, 0
> + svc_entry trace=0
>
> ARM( msr cpsr_c, #ABT_MODE | PSR_I_BIT | PSR_F_BIT )
> THUMB( mov r0, #ABT_MODE | PSR_I_BIT | PSR_F_BIT )
> @@ -353,7 +353,7 @@ __fiq_abt:
>
> svc_exit_via_fiq
> UNWIND(.fnend )
> -ENDPROC(__fiq_svc)
> +ENDPROC(__fiq_abt)
>
> /*
> * User mode handlers
> @@ -365,7 +365,7 @@ ENDPROC(__fiq_svc)
> #error "sizeof(struct pt_regs) must be a multiple of 8"
> #endif
>
> - .macro usr_entry
> + .macro usr_entry, trace=1
> UNWIND(.fnstart )
> UNWIND(.cantunwind ) @ don't unwind the user space
> sub sp, sp, #S_FRAME_SIZE
> @@ -402,10 +402,12 @@ ENDPROC(__fiq_svc)
> @
> zero_fp
>
> + .if \trace
> #ifdef CONFIG_IRQSOFF_TRACER
> bl trace_hardirqs_off
> #endif
> ct_user_exit save = 0
> + .endif
> .endm
>
> .macro kuser_cmpxchg_check
> @@ -736,13 +738,13 @@ ENDPROC(ret_from_exception)
>
> .align 5
> __fiq_usr:
> - usr_entry
> + usr_entry trace=0
> kuser_cmpxchg_check
> mov r0, sp @ struct pt_regs *regs
> bl handle_fiq_as_nmi
> get_thread_info tsk
> - mov why, #0
> - b ret_to_user_from_irq
> + restore_user_regs fast = 0, offset = 0
> + UNWIND(.cantunwind )
> UNWIND(.fnend )
> ENDPROC(__fiq_usr)
>
> diff --git a/arch/arm/kernel/fiq.c b/arch/arm/kernel/fiq.c
> index 918875d96d5d..1743049c433b 100644
> --- a/arch/arm/kernel/fiq.c
> +++ b/arch/arm/kernel/fiq.c
> @@ -53,6 +53,7 @@
> })
>
> static unsigned long no_fiq_insn;
> +static struct pt_regs def_fiq_regs;
>
> /* Default reacquire function
> * - we always relinquish FIQ control
> @@ -60,8 +61,15 @@ static unsigned long no_fiq_insn;
> */
> static int fiq_def_op(void *ref, int relinquish)
> {
> - if (!relinquish)
> + if (!relinquish) {
> + /* Restore default handler and registers */
> + local_fiq_disable();
> + set_fiq_regs(&dfl_fiq_regs);
This variable was declared as def_fiq_regs .
> set_fiq_handler(&no_fiq_insn, sizeof(no_fiq_insn));
> + local_fiq_enable();
> +
> + /* FIXME: notify irq controller to standard enable FIQs */
I don't understand what we need to tell the irq controller at this point.
If we do want to mask sources of FIQ from arch code then in the case of
IPI_CPU_BACKTRACE we might be better off disabling it at point of
generation than at the interrupt controller (to avoid the long timeout).
> + }
>
> return 0;
> }
> @@ -151,5 +159,6 @@ void __init init_FIQ(int start)
> {
> unsigned offset = FIQ_OFFSET;
> no_fiq_insn = *(unsigned long *)(0xffff0000 + offset);
> + get_fiq_regs(&dfl_fiq_regs);
> fiq_start = start;
> }
>
>
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