Re: [PATCH v1] LoongArch: Handle special PC in unwind_next_frame()

[Bibo Mao]

On 2025/11/27 上午9:39, Tiezhu Yang wrote:
> On 2025/11/26 下午5:56, Bibo Mao wrote:
> > On 2025/11/26 下午5:09, Tiezhu Yang wrote:
> > > Cc: Bibo Mao <maobibo@xxxxxxxxxxx>
> ...
> > > +#if IS_ENABLED(CONFIG_KVM)
> > > +void (*get_kvm_entry_info)(unsigned long *old, unsigned long *new, 
> > > unsigned long *size);
> > > +EXPORT_SYMBOL_GPL(get_kvm_entry_info);
> > > +#endif
> > this method mixes kvm and unwind components and it is obvious hack 
> > method. If there are other modules which have the similar problem, how 
> > to handle it? Add get_MODULE_1_entry_info/get_MODULE_2_entry_info API :)
>
> Currently, there is no other similar issue and something that should not
> happen in the future, this is "concrete question concrete analysis" and
> "handle special cases with special methods".
If so, I can think LoongArch unwind method is nasty. If this method is 
special for KVM module. KVM prefer to compile the exception function 
with built-in method, rather than using this nasty method.

Just be curious, it is the same orc unwind method. why is clean with 
file arch/x86/kernel/unwind_orc.c, however there is special handling 
bt_address() in file arch/loongarch/kernel/unwind_orc.c ?

> > KVM module copy exception function to allocated memory, it breaks 
> > unwind rules. KVM can compile exception function in kernel and do not 
> > copy the exception functions or LoongArch kernel provides unwind hint 
> > APIs to handle it.
>
> That is better if it is possible for KVM, no general API for kernel IMO.
>
> > >   static inline unsigned long bt_address(unsigned long ra)
> ...
> > > +       get_kvm_entry_info = kvm_entry_info;
> > Is this API get_kvm_entry_info() general for all modules or kernel 
> > components?
>
> No, it is just to get the necessary exception info for this special KVM
> case, we can use something like EXPORT_SYMBOL_FOR_KVM_INTERNAL to avoid
> the potential misuse if possible (not tested yet).
>
> Thanks,
> Tiezhu