Messages in this thread | | | Date | Wed, 21 Sep 2022 13:25:04 -0700 (PDT) | Subject | Re: [PATCH -next v2 2/2] riscv: extable: add new extable type EX_TYPE_KACCESS_ERR_ZERO support | From | Palmer Dabbelt <> |
| |
On Sat, 27 Aug 2022 03:39:38 PDT (-0700), tongtiangen@huawei.com wrote: > > > 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@huawei.com/ >>> [2]https://lore.kernel.org/lkml/20220812070557.1028499-4-tongtiangen@huawei.com/ >>> >> >> 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.
Generally we need some use of the code in the upstream kernel to justify its existence. In this case I don't really see that: it's just another type that's exactly the same as the existing one, having some out of tree code that depends on making these types do something different isn't a sufficient justification.
| |