Re: [PATCH -next v2 2/2] riscv: extable: add new extable type EX_TYPE_KACCESS_ERR_ZERO support

[Tong Tiangen]

在 2022/8/26 16:16, Andrew Jones 写道:
> On Fri, Aug 26, 2022 at 02:44:48PM +0800, Tong Tiangen wrote:
> > 在 2022/8/25 19:06, Andrew Jones 写道:
> > > On Mon, Aug 15, 2022 at 03:20:25AM +0000, Tong Tiangen wrote:
> > > > Currently, The extable type EX_TYPE_UACCESS_ERR_ZERO is used by
> > > > __get/put_kernel_nofault(), but those helpers are not uaccess type, so we
> > > > add a new extable type EX_TYPE_KACCESS_ERR_ZERO which can be used by
> > > > __get/put_kernel_no_fault().
> > > >
> > > > Only refactor code without any functional changes.
> > >
> > > This isn't quite true. __get/put_kernel_nofault now sets a different
> > > extable type (as the commit message says). But, nothing special seems
> > > to be done with that, so there's effectively no functional change. Can
> > > you please elaborate on the motivation for this change? Where will the
> > > KACCESS type need to be distinguished from the UACCESS type?
> >
> > The introduction of EX_TYPE_KACCESS_ERR_ZERO does not change any function,
> > but makes a correct distinction in the actual type, indicating that there
> > are indeed some kaccess entries in extable. I think this optimization is
> > more clear and reasonable.
>
> Well, creating new types, just for new type sake, just bloats code.
>
> > A few weeks ago, I did something similar on arm64[1]. I think this
> > optimization can also be used on riscv.
> >
> > We can do some features that are used on uaccss but not applicable on
> > kaccess in the future[2].
> >
> > [1]
> > https://lore.kernel.org/lkml/20220621072638.1273594-2-tongtiangen@xxxxxxxxxx/
> > [2]https://lore.kernel.org/lkml/20220812070557.1028499-4-tongtiangen@xxxxxxxxxx/
>
> This is part of the information, but I had already found this. What's
> still missing to me are the riscv patches, or at least a riscv plan, for
> actually implementing something which requires kaccess and uaccess to have
> distinct types.
>
> Thanks,
> drew

At present, there is no such plan on riscv, because it is rely on 
hardware support.
I think this patch can be merged as a small code optimization and 
without any function change.

Thanks,
Tong.

> .