Messages in this thread | | | Date | Fri, 21 Oct 2022 20:23:12 +0800 | Subject | Re: [PATCH -next v2 2/2] riscv: extable: add new extable type EX_TYPE_KACCESS_ERR_ZERO support | From | Tong Tiangen <> |
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在 2022/9/22 4:25, Palmer Dabbelt 写道: > 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. > . Hi palmer:
I agree with this point very much,many thanks.
Tong.
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