Re: [PATCH v2 0/3] Handle delay slot for extable lookup

[Jiaxun Yang]

在 2024/2/2 18:39, Linus Torvalds 写道:
> On Fri, 2 Feb 2024 at 04:30, Jiaxun Yang <jiaxun.yang@xxxxxxxxxxx> wrote:
> >        ptrace: Introduce exception_ip arch hook
> >        MIPS: Clear Cause.BD in instruction_pointer_set
> >        mm/memory: Use exception ip to search exception tables
> Just to clarify: does that second patch fix the problem that
> __isa_exception_epc() does a __get_user()?
>
> Because that mm/memory.c use of "exception_ip()" most definitely
> cannot take a page fault.

I reconsidered this issue today and I believe that exception_ip() usage 
here won't trigger
page_fault anyway.

Given that exception_ip is guarded by !user_mode(regs), EPC must points 
to a kernel
text address. There is no way accessing kernel text will generate such 
exception..

Thanks
> So if MIPS cannot do that whole exception IP thing without potentially
> touching user space, I do worry that we might just have to add a
>
>     #ifndef __MIPS__
>
> around this all.
>
> Possibly somehow limited to just the microMIPS/MIPS16e case in Kconfig instead?
>
>              Linus

--
---
Jiaxun Yang