Re: [PATCH -next v4 3/7] arm64: add support for machine check error safe

[Tong Tiangen <tongtiangen@huawei.com>]

在 2022/5/25 16:30, Mark Rutland 写道:
> On Thu, May 19, 2022 at 02:29:54PM +0800, Tong Tiangen wrote:
>>
>>
>> 在 2022/5/13 23:26, Mark Rutland 写道:
>>> On Wed, Apr 20, 2022 at 03:04:14AM +0000, Tong Tiangen wrote:
>>>> During the processing of arm64 kernel hardware memory errors(do_sea()), if
>>>> the errors is consumed in the kernel, the current processing is panic.
>>>> However, it is not optimal.
>>>>
>>>> Take uaccess for example, if the uaccess operation fails due to memory
>>>> error, only the user process will be affected, kill the user process
>>>> and isolate the user page with hardware memory errors is a better choice.
>>>
>>> Conceptually, I'm fine with the idea of constraining what we do for a
>>> true uaccess, but I don't like the implementation of this at all, and I
>>> think we first need to clean up the arm64 extable usage to clearly
>>> distinguish a uaccess from another access.
>>
>> OK,using EX_TYPE_UACCESS and this extable type could be recover, this is
>> more reasonable.
> 
> Great.
> 
>> For EX_TYPE_UACCESS_ERR_ZERO, today we use it for kernel accesses in a
>> couple of cases, such as
>> get_user/futex/__user_cache_maint()/__user_swpX_asm(),
> 
> Those are all user accesses.
> 
> However, __get_kernel_nofault() and __put_kernel_nofault() use
> EX_TYPE_UACCESS_ERR_ZERO by way of __{get,put}_mem_asm(), so we'd need to
> refactor that code to split the user/kernel cases higher up the callchain.
> 
>> your suggestion is:
>> get_user continues to use EX_TYPE_UACCESS_ERR_ZERO and the other cases use
>> new type EX_TYPE_FIXUP_ERR_ZERO?
> 
> Yes, that's the rough shape. We could make the latter EX_TYPE_KACCESS_ERR_ZERO
> to be clearly analogous to EX_TYPE_UACCESS_ERR_ZERO, and with that I susepct we
> could remove EX_TYPE_FIXUP.
> 
> Thanks,
> Mark.
According to your suggestion, i think the definition is like this:

#define EX_TYPE_NONE                    0
#define EX_TYPE_FIXUP                   1    --> delete
#define EX_TYPE_BPF                     2
#define EX_TYPE_UACCESS_ERR_ZERO        3
#define EX_TYPE_LOAD_UNALIGNED_ZEROPAD  4
#define EX_TYPE_UACCESS		        xx   --> add
#define EX_TYPE_KACCESS_ERR_ZERO        xx   --> add
[The value defined by the macro here is temporary]

There are two points to modify:

1、_get_kernel_nofault() and __put_kernel_nofault()  using 
EX_TYPE_KACCESS_ERR_ZERO, Other positions using 
EX_TYPE_UACCESS_ERR_ZERO keep unchanged.

2、delete EX_TYPE_FIXUP.

There is no doubt about others. As for EX_TYPE_FIXUP, I think it needs 
to be retained, _cond_extable(EX_TYPE_FIXUP) is still in use in assembler.h.

Thanks,
Tong.

> .