[RFC PATCH v2 1/3] mm/gup: fix gup_fast with dynamic page table folding
jgg at ziepe.ca
Wed Sep 9 14:03:24 EDT 2020
On Wed, Sep 09, 2020 at 07:25:34PM +0200, Gerald Schaefer wrote:
> I actually had to draw myself a picture to get some hold of
> this, or rather a walk-through with a certain pud-crossing
> range in a folded 3-level scenario. Not sure if I would have
> understood my explanation above w/o that, but I hope you can
> make some sense out of it. Or draw yourself a picture :-)
What I don't understand is how does anything work with S390 today?
If the fix is only to change pxx_addr_end() then than generic code
like mm/pagewalk.c will iterate over a *different list* of page table
It's choice of entries to look at is entirely driven by pxx_addr_end().
Which suggest to me that mm/pagewalk.c also doesn't work properly
today on S390 and this issue is not really about stack variables?
Fundamentally if pXX_offset() and pXX_addr_end() must be consistent
together, if pXX_offset() is folded then pXX_addr_end() must cause a
single iteration of that level.
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