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Message-ID: <7a028a4d-71f0-7064-cc1c-0ca50749ef2e@loongson.cn>
Date:   Thu, 29 Dec 2022 14:54:39 +0800
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Subject: Re: [PATCH] LoongArch: Fix irq enable in exception handlers
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To:     Jinyang He <hejinyang@loongson.cn>,
        Huacai Chen <chenhuacai@kernel.org>
Cc:     WANG Xuerui <kernel@xen0n.name>,
        Tiezhu Yang <yangtiezhu@loongson.cn>,
        loongarch@lists.linux.dev, linux-kernel@vger.kernel.org
References: <20221221074238.6699-1-hejinyang@loongson.cn>
 <CAAhV-H6VX=d1oymY0rh-mwOPMuBsYd7C9RzQat8BmmnrJ7apng@mail.gmail.com>
 <8eaea09e-67b0-5e51-4632-2c31a4c56a3e@loongson.cn>
 <CAAhV-H7maW1YWhfvCzYVix=aCMMFbx0KkGodaBjka4ThunBO5Q@mail.gmail.com>
 <1c578efd-ae8a-2d80-e505-a09b1a2f7eaa@loongson.cn>
 <b267cab1-3df4-6263-9c83-0061f20dd4a4@loongson.cn>
 <2364400d-bb1e-cbe2-8a65-adbe87186938@loongson.cn>
From:   Qi Hu <huqi@loongson.cn>
In-Reply-To: <2364400d-bb1e-cbe2-8a65-adbe87186938@loongson.cn>
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On 2022/12/29 14:13, Jinyang He wrote:
> On 2022-12-29 00:51, Qi Hu wrote:
>
>>
>> On 2022/12/27 18:10, Jinyang He wrote:
>>> On 2022-12-27 17:52, Huacai Chen wrote:
>>>
>>>> On Tue, Dec 27, 2022 at 5:30 PM Jinyang He <hejinyang@loongson.cn> 
>>>> wrote:
>>>>>
>>>>> On 2022-12-27 15:37, Huacai Chen wrote:
>>>>>> Hi, Jinyang,
>>>>>>
>>>>>> Move die_if_kernel to irq disabled context to solve what?
>>>>> For more strict logical. If the code flow go to die in 
>>>>> die_if_kernel(),
>>>>> its interrupt state is enable, that means it may cause schedule.
>>>>> So I think it is better to call die_if_kernel() firstly.
>>>> die_if_kernel is called with irq enabled in old kernels for several
>>>> years, and has no problems.
>>>
>>>
>>> I think because it never call die() in die_if_kernel(). What I do
>>> emphasize is that there needs to be more strict logic here than
>>> it worked well in the past. I bet if die_if_kernel() was removed,
>>> it will still work well in the future.
>>>
>>>
>>>>
>>>>>
>>>>>>    And LBT is
>>>>>> surely allowed to be triggered in kernel context.
>>>>> I'm not familar with lbt, I just not see any lbt codes in kernel. 
>>>>> Plz,
>>>>> how lbt exception triggered, and how kernel trigger lbt exception?
>>>> You can ask Huqi for more details, and this was discussed publicly 
>>>> last week.
>>>
>>> To: Qi Hu
>>>
>>>
>>> Hi,
>>>
>>>
>>> We really need some help. Can you give us some ideas?
>>>
>>>
>>> Thanks,
>>>
>>> Jinyang
>>>
>> Huacai is correct. The LBT disable exception (BTD) can be triggered 
>> in kernel context.
>>
>> If the CSR.ENEU.BTE == 0 [^1], the LBT instructions (these [^2] will 
>> be used in the kernel) will trigger the exception.
>>
>> Unfortunately, when you want to do some fpu_{save, restore}, you need 
>> to use some LBT instructions [^3] [^4]. So if FPD is triggered, LBT 
>> might still not be enabled, and the 'do_lbt' will be called in the 
>> kernel context.
>>
>> Hope the information can help. Thanks.
>>
>>
>> [1] 
>> https://loongson.github.io/LoongArch-Documentation/LoongArch-Vol1-EN.html#extended-component-unit-enable
>>
>> [2] 
>> https://github.com/loongson/linux/pull/4/files#diff-381d03cf86e2796d280e2fc82c005409d5e44b4bbbf90dd0dc17f5f0fa5553f1R140-R184
>>
>> [3] 
>> https://github.com/loongson/linux/pull/4/files#diff-381d03cf86e2796d280e2fc82c005409d5e44b4bbbf90dd0dc17f5f0fa5553f1R218-R230
>>
>> [4] 
>> https://github.com/loongson/linux/pull/4/files#diff-381d03cf86e2796d280e2fc82c005409d5e44b4bbbf90dd0dc17f5f0fa5553f1R236-R263
>>
>>
> Hi,
>
>
> That's helpful. Thanks!
>
>
> But I still wonder if SXD or ASXD have the same possibility of being 
> triggered in the kernel mode by sc_save_{lsx, lasx} or other place. Do 
> we need remove these die_if_kernel codes in do_lasx() and do_lsx()?
>
>
> Jinyang
>
Hi Jinyang,

I think only BTD has this tricky situation, because there is some 
overlap between FPD/SXD/ASXD and BTD.

So, in my view, SXD or ASXD will not be triggered in kernel mode.

Thanks.


Qi

>
>> Qi
>>
>>>
>>>> Huacai
>>>>>
>>>>> Thanks,
>>>>>
>>>>> Jinyang
>>>>>
>>>>>
>>>>>> Huacai
>>>>>>
>>>>>> On Wed, Dec 21, 2022 at 3:43 PM Jinyang He 
>>>>>> <hejinyang@loongson.cn> wrote:
>>>>>>> The interrupt state can be got by regs->csr_prmd. Once previous
>>>>>>> interrupt state is disable, we shouldn't enable interrupt if we
>>>>>>> triggered exception which can be triggered in kernel mode. So
>>>>>>> conditionally enable interrupt. For those do_\exception which
>>>>>>> can not triggered in kernel mode but need enable interrupt, call
>>>>>>> die_if_kernel() firstly. And for do_lsx, do_lasx and do_lbt cannot
>>>>>>> triggered in kernel mode, too.
>>>>>>>
>>>>>>> Signed-off-by: Jinyang He <hejinyang@loongson.cn>
>>>>>>> ---
>>>>>>>    arch/loongarch/kernel/traps.c | 19 ++++++++++---------
>>>>>>>    1 file changed, 10 insertions(+), 9 deletions(-)
>>>>>>>
>>>>>>> diff --git a/arch/loongarch/kernel/traps.c 
>>>>>>> b/arch/loongarch/kernel/traps.c
>>>>>>> index 1ea14f6c18d3..3ac7b32d1e15 100644
>>>>>>> --- a/arch/loongarch/kernel/traps.c
>>>>>>> +++ b/arch/loongarch/kernel/traps.c
>>>>>>> @@ -340,9 +340,9 @@ asmlinkage void noinstr do_fpe(struct 
>>>>>>> pt_regs *regs, unsigned long fcsr)
>>>>>>>
>>>>>>>           /* Clear FCSR.Cause before enabling interrupts */
>>>>>>>           write_fcsr(LOONGARCH_FCSR0, fcsr & ~mask_fcsr_x(fcsr));
>>>>>>> -       local_irq_enable();
>>>>>>>
>>>>>>>           die_if_kernel("FP exception in kernel code", regs);
>>>>>>> +       local_irq_enable();
>>>>>>>
>>>>>>>           sig = SIGFPE;
>>>>>>>           fault_addr = (void __user *) regs->csr_era;
>>>>>>> @@ -432,7 +432,8 @@ asmlinkage void noinstr do_bp(struct pt_regs 
>>>>>>> *regs)
>>>>>>>           unsigned long era = exception_era(regs);
>>>>>>>           irqentry_state_t state = irqentry_enter(regs);
>>>>>>>
>>>>>>> -       local_irq_enable();
>>>>>>> +       if (regs->csr_prmd & CSR_PRMD_PIE)
>>>>>>> +               local_irq_enable();
>>>>>>>           current->thread.trap_nr = read_csr_excode();
>>>>>>>           if (__get_inst(&opcode, (u32 *)era, user))
>>>>>>>                   goto out_sigsegv;
>>>>>>> @@ -514,7 +515,8 @@ asmlinkage void noinstr do_ri(struct pt_regs 
>>>>>>> *regs)
>>>>>>>           unsigned int __user *era = (unsigned int __user 
>>>>>>> *)exception_era(regs);
>>>>>>>           irqentry_state_t state = irqentry_enter(regs);
>>>>>>>
>>>>>>> -       local_irq_enable();
>>>>>>> +       if (regs->csr_prmd & CSR_PRMD_PIE)
>>>>>>> +               local_irq_enable();
>>>>>>>           current->thread.trap_nr = read_csr_excode();
>>>>>>>
>>>>>>>           if (notify_die(DIE_RI, "RI Fault", regs, 0, 
>>>>>>> current->thread.trap_nr,
>>>>>>> @@ -606,8 +608,8 @@ asmlinkage void noinstr do_fpu(struct 
>>>>>>> pt_regs *regs)
>>>>>>>    {
>>>>>>>           irqentry_state_t state = irqentry_enter(regs);
>>>>>>>
>>>>>>> -       local_irq_enable();
>>>>>>>           die_if_kernel("do_fpu invoked from kernel context!", 
>>>>>>> regs);
>>>>>>> +       local_irq_enable();
>>>>>>>           BUG_ON(is_lsx_enabled());
>>>>>>>           BUG_ON(is_lasx_enabled());
>>>>>>>
>>>>>>> @@ -623,13 +625,13 @@ asmlinkage void noinstr do_lsx(struct 
>>>>>>> pt_regs *regs)
>>>>>>>    {
>>>>>>>           irqentry_state_t state = irqentry_enter(regs);
>>>>>>>
>>>>>>> +       die_if_kernel("do_lsx invoked from kernel context!", regs);
>>>>>>>           local_irq_enable();
>>>>>>>           if (!cpu_has_lsx) {
>>>>>>>                   force_sig(SIGILL);
>>>>>>>                   goto out;
>>>>>>>           }
>>>>>>>
>>>>>>> -       die_if_kernel("do_lsx invoked from kernel context!", regs);
>>>>>>>           BUG_ON(is_lasx_enabled());
>>>>>>>
>>>>>>>           preempt_disable();
>>>>>>> @@ -645,14 +647,13 @@ asmlinkage void noinstr do_lasx(struct 
>>>>>>> pt_regs *regs)
>>>>>>>    {
>>>>>>>           irqentry_state_t state = irqentry_enter(regs);
>>>>>>>
>>>>>>> +       die_if_kernel("do_lasx invoked from kernel context!", 
>>>>>>> regs);
>>>>>>>           local_irq_enable();
>>>>>>>           if (!cpu_has_lasx) {
>>>>>>>                   force_sig(SIGILL);
>>>>>>>                   goto out;
>>>>>>>           }
>>>>>>>
>>>>>>> -       die_if_kernel("do_lasx invoked from kernel context!", 
>>>>>>> regs);
>>>>>>> -
>>>>>>>           preempt_disable();
>>>>>>>           init_restore_lasx();
>>>>>>>           preempt_enable();
>>>>>>> @@ -666,6 +667,7 @@ asmlinkage void noinstr do_lbt(struct 
>>>>>>> pt_regs *regs)
>>>>>>>    {
>>>>>>>           irqentry_state_t state = irqentry_enter(regs);
>>>>>>>
>>>>>>> +       die_if_kernel("do_lbt invoked from kernel context!", regs);
>>>>>>>           local_irq_enable();
>>>>>>>           force_sig(SIGILL);
>>>>>>>           local_irq_disable();
>>>>>>> @@ -677,7 +679,6 @@ asmlinkage void noinstr do_reserved(struct 
>>>>>>> pt_regs *regs)
>>>>>>>    {
>>>>>>>           irqentry_state_t state = irqentry_enter(regs);
>>>>>>>
>>>>>>> -       local_irq_enable();
>>>>>>>           /*
>>>>>>>            * Game over - no way to handle this if it ever 
>>>>>>> occurs. Most probably
>>>>>>>            * caused by a fatal error after another 
>>>>>>> hardware/software error.
>>>>>>> @@ -685,8 +686,8 @@ asmlinkage void noinstr do_reserved(struct 
>>>>>>> pt_regs *regs)
>>>>>>>           pr_err("Caught reserved exception %u on pid:%d [%s] - 
>>>>>>> should not happen\n",
>>>>>>>                   read_csr_excode(), current->pid, current->comm);
>>>>>>>           die_if_kernel("do_reserved exception", regs);
>>>>>>> +       local_irq_enable();
>>>>>>>           force_sig(SIGUNUSED);
>>>>>>> -
>>>>>>>           local_irq_disable();
>>>>>>>
>>>>>>>           irqentry_exit(regs, state);
>>>>>>> -- 
>>>>>>> 2.34.3
>>>>>>>
>>>>>
>>>
>>
>