On Sun, Sep 20 2020 at 08:41, Thomas Gleixner wrote:
On Sat, Sep 19 2020 at 10:18, Linus Torvalds wrote:
Maybe I've missed something. Is it because the new interface still does "pagefault_disable()" perhaps?
But does it even need the pagefault_disable() at all? Yes, the *atomic* one obviously needed it. But why does this new one need to disable page faults?
It disables pagefaults because it can be called from atomic and non-atomic context. That was the point to get rid of
if (preeemptible()) kmap(); else kmap_atomic();If it does not disable pagefaults, then it's just a lightweight variant of kmap() for short lived mappings.
Actually most usage sites of kmap atomic do not need page faults to be disabled at all. As Daniel pointed out the implicit pagefault disable enforces copy_from_user_inatomic() even in places which are clearly preemptible task context.
As we need to look at each instance anyway we can add the PF disable explicitely to the very few places which actually need it.
Thanks,
tglx