Re: [RFC PATCH v2 03/19] vbus: add connection-client helper infrastructure

[Avi Kivity]

Gregory Haskins wrote:

   

> > BTW, why did you decide to use get_user_pages?
> > Would switch_mm + copy_to_user work as well
> > avoiding page walk if all pages are present?
> >   
> >     
>
> Well, basic c_t_u() won't work because its likely not "current" if you
> are updating the ring from some other task, but I think you have already
> figured that out based on the switch_mm suggestion.  The simple truth is
> I was not familiar with switch_mm at the time I wrote this (nor am I
> now).  If this is a superior method that allows you to acquire
> c_t_u(some_other_ctx) like behavior, I see no problem in changing.  I
> will look into this, and thanks for the suggestion!
>   

copy_to_user() is significantly faster than get_user_pages() + kmap() + 
memcmp() (or their variants).

--
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.

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