linux-kernel - Re: [PATCH -next v2 2/2] riscv: extable: add new extable type EX_TYPE_KACCESS_ERR

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Date:   Fri, 26 Aug 2022 14:44:48 +0800
From:   Tong Tiangen <tongtiangen@...wei.com>
To:     Andrew Jones <ajones@...tanamicro.com>
CC:     Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Palmer Dabbelt <palmer@...osinc.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        <Conor.Dooley@...rochip.com>, <linux-riscv@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <wangkefeng.wang@...wei.com>,
        Guohanjun <guohanjun@...wei.com>
Subject: Re: [PATCH -next v2 2/2] riscv: extable: add new extable type
 EX_TYPE_KACCESS_ERR_ZERO support



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.

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@huawei.com/
[2]https://lore.kernel.org/lkml/20220812070557.1028499-4-tongtiangen@huawei.com/

Thanks,
Tong.

> 
> Thanks,
> drew
> .