Re: [RFC PATCH] ARM: enable irq in translation/section permission fault handlers

[Bernd Edlinger <bernd.edlinger@hotmail.de>]

On 2/20/19 12:00 PM, Sebastian Andrzej Siewior wrote:
> 
> Bernd Edlinger explained the missing piece to me. With
> PAGE_OFFSET=0xC0000000 and without LPAE a R/W of 0xbffffff0 will ends up
> with:
> 

I am unable to reproduce on my target, wheter do_page_fault is directly taken,
or do_translation_fault is taken depends on whether the page table root directory
permission bits deny the access or the second level page table deny the access?

But if there is a way to get into the code path do_DataAbort->do_page_fault with
addr > TASK_SIZE, then I don't see why that works without the RT patch,
since the interrupts are enabled here:

do_page_fault(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
{
        struct task_struct *tsk;
        struct mm_struct *mm;
        int sig, code;
        vm_fault_t fault;
        unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;

        if (notify_page_fault(regs, fsr))
                return 0;

        tsk = current;
        mm  = tsk->mm;

        /* Enable interrupts if they were enabled in the parent context. */
        if (interrupts_enabled(regs))
                local_irq_enable();

Is preemption disabled at this point, without the RT patch?

I still don't quite see why is this no issue without the RT patch.
Can someone explain that?


Thanks
Bernd.
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