Re: [Xen-devel] [PATCH v2] x86: correct create_bounce_frame

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 05.05.17 at 12:18, <andrew.cooper3@xxxxxxxxxx> wrote:
> On 05/05/17 10:38, Jan Beulich wrote:
>>>>> On 05.05.17 at 10:41, <andrew.cooper3@xxxxxxxxxx> wrote:
>>> On 04/05/17 14:35, Jan Beulich wrote:
>>>> @@ -345,24 +344,30 @@ UNLIKELY_START(z, create_bounce_frame_ba
>>>>  __UNLIKELY_END(create_bounce_frame_bad_bounce_ip)
>>>>          movq  %rax,UREGS_rip+8(%rsp)
>>>>          ret
>>>> -        _ASM_EXTABLE(.Lft2,  domain_crash_page_fault_32)
>>>> -        _ASM_EXTABLE(.Lft3,  domain_crash_page_fault_24)
>>>> -        _ASM_EXTABLE(.Lft4,  domain_crash_page_fault_8)
>>>> -        _ASM_EXTABLE(.Lft5,  domain_crash_page_fault_16)
>>>> -        _ASM_EXTABLE(.Lft6,  domain_crash_page_fault)
>>>> -        _ASM_EXTABLE(.Lft7,  domain_crash_page_fault)
>>>> -        _ASM_EXTABLE(.Lft12, domain_crash_page_fault_8)
>>>> -        _ASM_EXTABLE(.Lft13, domain_crash_page_fault)
>>>> +        _ASM_EXTABLE(.Lft2,  domain_crash_page_fault_6x8)
>>>> +        _ASM_EXTABLE(.Lft3,  domain_crash_page_fault_5x8)
>>>> +        _ASM_EXTABLE(.Lft4,  domain_crash_page_fault_4x8)
>>>> +        _ASM_EXTABLE(.Lft5,  domain_crash_page_fault_3x8)
>>> Do you perhaps mean to swap the labels for 4 and 5?
>> Oh, yes, of course. I remember that something was odd when
>> doing the conversion, but I wasn't able to spot it because things
>> looked well ordered.
>>
>> Having made a mistake like this I wonder whether it wouldn't be
>> better to move these next to their instructions anyway? The
>> way we build them now both insn and extable generation could
>> actually be bundled into a macro, eliminating any risk for the
>> two parts to go out of sync ...
> 
> Do you see such a construct being used anywhere else?  I can't spot any
> obvious candidates.

No, just here. But it's eight places.

> For post 4.9, I will be submitting a series which reimplements this
> logic in C, so I wouldn't expend too much effort in this area.

True, yet I'm touching all these lines now anyway... Would you
be opposed to moving them and/or macroizing the whole thing?

Jan


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